MINISTERUL GEOLOGIEI INSTITUTUL DE GEOLOGIE SI GEOFIZICĂ VOL LXIV Les auteurs assument la responsabilite des donn66s publiăes Institutul Geologic al României MINISTERUL GEOLOGIEI INSTITUTUL DE GEOLOGIE ȘI GEOFIZICĂ MINISTERE DE LA GEOLOGIE INSTITUT DE GEOLOGIE ET DE GEOPHYSIQUE ANUARUL INSTITUTULUI DE GEOLOGIE ȘI GEOFIZICĂ AmâlRE OE INSTITUT DE GEOLOGIE ET OE GEOFHYSWVE tome LXIV Volum specia!, editat cu ocazia celui de a! 27-les CONGRES GEOLOGIC INTERNAȚIONAL MOSCOVA 1984 Volume special, edite a Toccasion du 27e CONGRES GEOLOGIQUE INTERNATIONAL MOSCOU 1984 BUCUREȘTI 1984 Institutul Geological României Institutul Geological României CONTENU PETROLOGIE—MINERALOGIE Balintoni I. Polymetamonphism, a Discussion Based on Examples from the Romanian Carpathians................................................. 7 Bercia I., Hârtopanu I., Șeclăman M. Curves of Mineral Isorelations, a Concrete Method to Research Metamorphism Conditions .... 17 Berza T., lancu V., Hann H. P., Seghedi A. Dynamic and Retrograde Meta- morphism : Examples from the Romanian South Carpathians ... 25 Constantinescu E., Săbău G. Mineralogy of Alpine Veins from the Romanian Carpathians ............................................................. . 33 Hârtopanu I-, Șeclăman M. Equilibrium Geosurfaces Dynamics of Mineral Parageneses . ....................................... 45 lancu V., Udubașa G„ Rădan S., Visarion A. Complex Criteria of Separating Weakly Metamorphosed Formations. An Example : the South Car- pathians .............................................................. 51 K lanovici V., Neacșu Gh., Neacșu V. Interstratified Clay Minerals in the Harghita Mountains, Romania......................................................61 Jude R., Jude L. Eruptive Breccias Associated with Some Tertiary Mag- matites from Romania.................................................... 67 Pomârleanu V., Pomârleanu-Neagu E. Fluid Inclusions in Hydrothermal Calcite and Their Significance in Crystallogenesis ...... 77 Pop N., Udubașa G., Edelstein O., Pop V., Kovacs M., Damian Gh., Istvan D., Stan D., Bernad A. A Bimodal Igneous Complex of Neogene Age, Țibleș, East Carpathians, Romania...................................... 81 Popescu Gh-, Preda I., Nedelcu C. Le metamorphisme des charbons des Carpathes Meridionales roumaines.........................................91 / Rădulescu D. Continuity, Periodicity and Episodicity in Magma Genesis Processes Associated to the Closing of the Alpine Ocean in the Carpathian Area.................................................................103 Russo-Săndulescu D., Vâjdea E., Tănăsescu A. Neocretaceous-Paleogene Sub- duction Igneous Rocks in the Romanian Carpathians — Mutual Rela- tionships, Succession and Areal Distrifoution...........................111 Savu H., Udrescu C-, Neacșu V., Stoian M. Trends of Tholeiitic Magma Differentiation of the Sheeted Dyke Complex from the Mureș Zone (Romania)...............................................................121 Strutinski C., Paica M., Pop N. Chloritization of Biotites and Its Bearing on K-Aj? Ages of Some Alpine Magmatites from the Poiana Rusca Massif 133 Udubașa G. Typomorphism of Some Ore Minerals and a PVT Classification of Certam Ore Deposits..................................................141 Institutul Geologic al României 4 CONTENU 2 GISEMENTS Berbeleac I-, Ștefan A. Ore Texture and Structure of Sulphide-Iron Oxides of the Precambrian Altîn Tepe Deposit, Dobrogea.....................153 Boștinescu S. Porphyry-Copper Systems in the South Apuseni Mountains — Romania...........................................................161 Ciofiica Gr., Vlad Ș. Alpine Metallogeny in Romania.......................175 Mîrza I. The Tectostructural Factor, a Fundamental Criterium to Outline the Metallogenetic (Petrometallogenetic) Provinces — Exemplification on the Romanian Territory...........................................185 Năstăseanu S. Geology of the Main Coal Deposits in Romania................196 Paraschiv D. The Evolution of the Hydrocarbon Field Distribution in the Moesian Platform..........................J .............205 Paraschiv D- On the Natural Degasification of the Hydrocarbon-Beâring Deposits in Romania............................................... 215 Răduț M., Fotopolos S., Edelstein O., Hannich D., Istvan D., Gașcu C., Bîlcu T. Physical-Geological Models Regarding the Neoeruptive Rocks in the Baia Mare Area : A Contribution to the Study of Some Metal- logenetic Structures................................................... 221 Stanciu C. Hypogene Alteration Genetic Types Related to the Neogene Vol- canism of the East Carpathians, Romania.............................235 STRATIGRAPHIE—PALEONTOLOGIE Balteș N. Palynofacies. Stratigraphic-Paleontologic Concept and Geological Exploration Tool.................................................. 245 Costea I., Roșa A., Demetrescu D. Etude stratigraphique du Senonien infe- rieur des Carpathes Orientales (Roumănie)...........................251 Iordan M. Biostratigraphy of the Silurian and Devonian in the Moldavian and Moesian Platforms (Romania).....................................259 Meszăros N. Nannoplankton Zones of the Paleogene and Neogene Deposits of the Transylvania................................................ 269 Moldovanu M. Palynology of the Tertiary Deposits in the Pannonian Depres- sion, Romania.......................................................275 Muțiu R. Stratigraphie des depots albiens de la plate-forme moesienne (secteur roumain).................................................. 283 Olaru L., Oniceanu M. Palynostratigraphie de quelques formations cristallo- phylliennes des Carpathes Orientales roumaines......................291 Szasz L., Ion J. Biostratigraphic Characterization of Some Boundaries in the Cenomanian-Coniacian Interval................................. 299 Turculeț I. Associations de Mollusques et Brachiopodes triasiques des Car- pathes Orientales roumaines et leur place dans le contexte biostra- tigraphique general alpino-carpathique............................ 309 Vinogradov C., Popescu M. Les facies carbonates du Paleozoîque de la plate-forme moesienne (Roumănie)....................................317 TECTONlQUE Lupu M. Problems of the European Continental Margin in the Transyl- vanian-Pannonian Area...............................................323 Ă Institutul Geologic al României 3 CONTENU 5 Pavelescu L., Nitu Gh. Some Characteristic Features of the South Carpathians 333 \ Săndulescu M. Compared Alpine Geotectonic Models........................343 Ștefănescu M. Interpretation of the Thrust Faults Genesis from an Alpine Chain Segment — East Carpathians..................................353 GEOPHYSIQUE Beșuțiu L. The Reflection of the Basaltic Layer in the Regional Anomaly of the Geomagnetic Field on the Romanian Territory................361 Căprărin M., Gaspar R., Năstase P., Popescu Al-, Toma D. Application de la metnode du profil slalom dans une zone comprise entre la vallee de la Dîmbovița et la vallee du Buzău............................3 69 Crețu I., Nechiti Gr., Vamvu V., Veliciu Ș. Geothermal Resources of Romania 381 Dicea O., lanăș M., Lungu A., Gheorghiu G., lonescu G., Taloș D. Para- digmes structuraux-depositionnels des fonnations pannonienp.es du secteur roumain de la depression pannonienne deduits par analyse et interpretation de prospections sismiques de reflection.................391 GEOTECHNIQUE—HYDROGEOLOGIE Bomboe P., Stroia FI. Evaluation of the Sliding Risk of Slopes in Conso- lidated Clays by Stochastic Simulation Methods....................401 Bordea I-, Moldoveanu Tr., Tudorache G. Aspects sur Fanalyse sismique des barrages (Roumanie)...............................................411 Gheorghe Al., Crăciun P. Models for Interpreting Some Hydrogeological and Thermic Characteristics of Geothermal Structures Situated in the East Of the Pannonian Depression.......................................421 Gheorghe Al., Scrădeanu D. Hydrogeological and Probabilistic Methods Used in the Study of Dewatering Systems for Coal Deposits .... 429 Pavelescu L., Privighetoriță C. Structural and Textural Study Concerning the Crystalline and Magmatic Rocks in the South Carpathians. Engi- neering-Geological Significance...................................439 SEDIMENTOLOGIE Anastasiu N., Jipa D. Source-Areas of the Assyntic Flysch Deposits in the Central Dobrogea Massi-f (Romania)................................445 Y Jipa D. Large Scale Progradation Structures in the Romanian Carpathians : Facts and Hypothesis......................................................455 V Mihăilescu N., Rogojină C. A Fluvial Sedimentation Model — the Danube Delta.................................................................... 465 IGR/ Institutul Geological României Petrologie-Mineralogie POLYMETAMORPHISM, A DISCUSSION BASED ON EXAMPLES FROM THE ROMANIAN CARPATHIANS by ION BALINTONI1 Introduction The present study is a discussion on regional or orogenic meta- morphism, as defined by Miyashiro (1975), with special reference to its mineralogical aspects. Regional metamorphism during Alpine time, characterized by low intensity and oecurring on small areas in the Romanian Carpathians, is left aside. The main notions used by the petrological study of metamorphics are : mineral association and para- genesis. A mineral association is a group of minerals which constitutes a metamorphite sample ; a paragenesis represents the synchronous mi- nerals of an association. This definition of the paragenesis is in agreement with Vernon’s definition (1976) but differs from Winkler’s (1976), according to which a paragenesis includes the minerals of an association placed in equilibrium, which implies their tangențial position on the one hand and the simultaneous occurrence of several synchronous parageneses in a mineral association on the other hand. We consider that the paragenesis defined by Winkler (1976) should be better called subparagenesis. By taking' into account a certain lithostratigraphic unit, the number of mineral associations will correspond, on the whole, to the number of petrographic types encountered and an equal number of .parageneses for the simplest case and an indeterminate but limited one for more complicated cases. To make things easier, the term of general mineral association should be used for all the minerals belong- ing to a certain lithostratigraphic unit and that of general paragenesis for all synchronous minerals of the same lithostratigraphic unit. The polymetamorphism designates the repeated action of regional metamor- phism factors on the same rock pile at great time intervals so that the periods of activity belong to different orogeneses (e.g., Hercynian, Cale- donian, Cadomian, etc.). Although one may speak of the impetuous development of the study of metamorphism during the last two decades, due to the progres» achieved by experimental petrology and the revo- 1 Institute of Geology and Geophysics, str Caransebeș 1, 78344 Bucharest. A Institutul Geologic al României VlGR/ 8 I. BALINTONI lution of earth Sciences brought about by global tectonics, the concept of polymetamorphism is not even mentioned by the most representative researchers of this time, such as Turner (1968), Miyashiro (1975), Winkler (1976) or Vernon (1976). Middle Paleozoic Formations The data regarding the Middle Paleozoic formations have been recently synthetized by Krăutner (in Săndulescu et al., 1981) for the East Carpathians, by Krăutner et al. (1981) for the South Carpathians and by Dimitrescu (in Rădulescu, Dimitrescu, 1982) for the Apuseni Mts. The Middle Paleozoic formations, proved by paleontological evidence, belong to the Ordovician-Lower Carboniferous interval and underwent metamorphism during Hercynian orogenesis, Sudetian phase ; the meta- morphics are unconformably overlain by non-metamorphosed Upper Carboniferous. In case the formations considered by some authors not to belong to the Middle Paleozoic are excluded (most of the Țibău Series and the Argestru Series of the East Carpathians — Balintoni, 1981, 1982, the Nădrag Series, the Bătrîna Series, the Govăjdia and Ghelar Series in Southern facies of the South Carpathians — Hîrtopanu, Balintoni in Udubașa et al., 1983, unpublished data), the general mineral associations of Hercynian metamorphics include only one general para- genesis, which belongs thermodynamically to the chlorite zone. The characteristic minerals of these general parageneses are : albite, epidote, clinozoisite, actinote, chlorite, stilpnomelane, chloritoid, lotrite (pum- pellyite), prehnite, sphene, rutile, sericiie, iron oxides. The Middle Paleo- zoic formations overlie transgressively the Early Caledonian metamor- phics or more ancient ones ; within them there is a stratigraphic unconformity between Devonian and older sequences. Late Precambrian-Lower Paleozoic Formations These formations are less known than the Middle Paleozoic ones. Organic remains are scarce, iill preserved and have a wide circulation in time. Isotopic ages are few and it is difficult to interpret them. Information about these sequences is given by Krăutner (1983) in con- nection with the East Carpathians, by Dimitrescu (1983) for the Apuseni Mts and by Krăutner et al. (1983 a) for the South Carpathians. Hârto- panu et al. (1982), Balintoni (1982) and Gheuca, Dinică (1983) argued for the non-inclusion of the Arada Formation, the Codru Complex and the Muncel Formation in the Apuseni Mts as well as of the Lerești Formation in the South Carpathians, in the Late Precambrian-Lower Paleozoic formations stated by the above mentioned authors. The Cibin Group in the South Carpathians is insufficiently proved paleontologically and petrographically. Thus, we leave it aside. Therefore, the Tulgheș Group in the East Carpathians and the Biharia Group in the Apuseni Mts will be commented upon. • Tulgheș Group. According to new paleontological data and to a new analysis of the existing paleontological and isotopic data, Iliescu Institutul Geologic al României xjgr/ 3 POLYMETAMORPHISM IN THE ROMANIAN CARPATHIANS 9 et al. (1983) assign the Tulgheș Group to the Cambrian age, marked by possible downward transition to the Vendian and upward one to the Lower Ordovieian. Balintoni, Chițimuș (1973) reported two metamorphic parageneses built up of metapelites of the Tulgheș Group, and con- sidered them an illustration of polymetamorphism. The authors men- tioned an older paragenesis made up of biotite and a rutile paramorph after brookite in equilibrium with albite, chlorite, muscovite and a second paragenesis consisting of chlorite after biotite, second generation light-ferriferrous rutile (resulted from the recrystallization of pre- existing rutile) and iron oxides as neoformation minerals. To the general parageneses of the Tulgheș Group may be also added epidote, clino- zoisite, actinote and sphene, bearing thermodynamic significance. The first paragenesis formed under static conditions. The second, conco- mitantly with the generation of a sometimes highly penetrating foliation in metapelites. The former paragenesis points to thermodynamic con- ditions in the biotite zone and the latter in the chlorite zone, being of regressive nature. Due to the prevalence of Hercynian K-Ar ages dis- closed by the study of rocks in the Tulgheș Group, the second para- genesis is assigned to Hercynian metamorphism and as far as the paleontologic ages of the Tulgheș Group are not greater than Lower Ordovieian, the first paragenesis may be considered Early Caledonian. The lowermoșt part of the Tulgheș Group is not known due to the Alpine and pre-Alpine overthrusts (Balintoni et al., 1983) and the uncertain occurrence of transgressively overlying Middle Paleozoic formations. Biharia Group. According to Balintoni (1982), the Biharia Group was proved paleontologically by Visarion (1970), Visarion, Dimitrescu (1971) and Solomon et al. (1981). The Biharia Group represents a mainly metabasite sequence. Giușcă (1979) reported the complex character of mineral associations of rocks in the Biharia Group, while Balintoni (1983) distinguished in the Highiș-Drocea massif two general parage- neses of regional metamorphism : a relict general magmatic para- genesis and a thermic contact paragenesis due to Upper Paleozoic gra- nitic intrusions. The older general metamorphic paragenesis, formed under static conditions includes : hastingsite hornblende, epidote I + al- bite I (within old plagioclases), sphene I (with relict ilmenite in the middle), biotite, almandine. From thermodynamic point of view, it is characteristic of the almandine zone or of the albite or epidote amphi- bolite facies (e.g. Miyashiro, 1975). The more recent general paragenesis, formed under dynamic conditions, includes.: actinote, chlorite, albite II, epidote II, sphene II, magnetite. The second generation albite is of porphyroblastic nature, epidote is iron poorer (frequently clinozoisite) and sphene does no longer include ilmenite relics. The minerals belong- ing to the second general paragenesis of regional metamorphism are iron poorer and the latter occurs as magnetite ; from thermodynamic point of view they enter the chlorite zone and are related to a penetrative foliation in which they range. As far as the Biharia Group alone is transgressively overlain by the Belioara Subgroup and probably the Păiușeni Subgroup, of Middle Paleozoic age, the second general para- A Institutul Geologic al României \ IGR> 10 I- BALINTONI 4 genesis is assigned to Hercynian metamorphism ; according to paleonto- logical data, the first general paragenesis may be assigned to the Early Caledonian age, the metamorphic history of the Biharia Group being similar to that one of the Tulgheș Group. The lowermost part of the Biharia Group is not known ; this group forms the most important part of the Alpine Biharia Nappe. As regards the Late Precambrian-Lower Paleozoic formations, the following characteristics are to be noted : two general parageneses of regional metamorphism ; the regressive aspect and the local occurrence of the second related to a penetrative foliation ; the essentially static character of the former ; the variable intensity, but not too high, of the first metamorphism ; the omission of some zonations of the first metamorphism. Precambrian Formations Recent syntheses on the Precambrian Carpathian formations have been carried out by Krăutner (1980, 1983), Krăutner et al. (1981), Krăutner, Balintoni (in Săndulescu et al., 1981), Krăutner et al. (1983 a, b), Dimitrescu (1983), lancu (1983). According to Krăutner et al. (1983 a, b) they are of Middle Proterozoic age (1650 + -50 to 850— 1000 m.y.), their inițiali metamorphism -belongs to Grenvillian orogeny and lower and upper Middle Precambrian formations can be distin- guished by means of supenposition. The same authors consider that the following metamorphism belongs to Early Caledonian orogeny and there is a pre-metamorphic sequence Upper Precambrian-Lower Paleozoic in age. Salop’s {1983) division of the Precambrian points to the Neopro- terozoic as part of the former sequence of Precambrian formations men- tioned above, while the Epiproterozoic is conformable with the Eocam- brian (Vendian) and the Lower Paleozoic. lancu (1983) reports even a pre-Grevillian age for some South Carpathian metamorphics and also admits other Grenvillian and Assyntic ones. The existing objective data render hypothetical the pre-Grenvilllian metamorphics, while the Gren- villian ones are supported by two isotopic ages only : Rb-Sr age of 842 m.y. (Bagdasarian, 1972, fide Krăutner et al., 1983 a) for the South Carpathian Sebeș-Lotru Group and K-Ar age of 748 m.y. (Semenenko et al., 1969, fide Krăutner, 1983) for the East Carpathian Bretila Group. As regards the division of Middle Proterozoic into lower and upper (Krăutner et al., 1983 a, b) by means of conformity between Cumpăna Group and Făgăraș Group in the Făgăraș Mts (Krăutner, 1980), recent studies (Balintoni, 1983, unpu'blished data) have pointed to a tectonic relationship between the two groups all over the massif and thus to the non-validity of the dividing criterion. Finally, in the Danubian meta- morphic formations in the South Carpathians and the Rebra Group in the East Carpathians, the U-Pb ages from granițe zircons and K-Ar ages of 601—667 m.y. were reported (Grunfelder et al., 1981, fide Krăutner et al., 1983 a ; Mînzatu et al., 1975, fide Krăutner, 1983). These account for Cadomian orogenesis. Institutul Geologic al României A ig r7 5 POLYMETAMORPHISM IN THE ROMANIAN CARPATHIANS 11 Parageneses of the Rebra Group. Balintoni, Gheuca (1977) have described in the general mineral associations' of the rocks in the Rebra Group from the Bistrița Mts, three parageneses which account for dif- ferent thermodynamic fields during their genesis : (1) staurolite, kyanite pointing to Barrovian-type metamorphism ; (2) andalusite, cordierite generated under static conditions at the expense of the former, posterior to the generation of a highly penetrative foliation which affects the paragenesis (1) mechanically. Paragenesis (2) is a high temperature and low pressure one. In some places, posterior to the mentioned penetrative foliation, one notices fibroblastic sillimanite generated on biotite. The relationship sillimanite-paragenesis (2) is however unclear ; in the Lăpuș Mts where the sillimanite is of the same generation as the one in the Bistrița Mts ; andalusite and cordierite are lacking. Paragenesis (2) shows limîted extension. At the top of the formations belonging to the Rebra Group it is to note a general paragenesis (3) including chlorite, albite, epidote, actinote, characteristic of the chlorite zone and formed on pre- existing minerals. The authors cited above have assigned the first para- genesis to Cadomian metamorphism, the second to Early Caledonian metamorphism and the third to Hercynian metamorphism. Parageneses of the Sebeș-Lotru Group. Bercia (1975) and parti- cularly Hârtopanu (1982) have shown the remarkable paragenetic com- plexity of the rocks belonging to this group. From some areas of the South Carpathians, mainly from metapelites, they reported some para- geneses including the following index minerals for specific fields of thermodynamic factors : (1) staurolite, kyanite, prior to strong defor- mational stage ; (2) staurolite, kyanite + sillimanite, posterior to the mentioned deformational stage ; (3) andalusite, cordierite + sillimanite, also posterior to the same deformational stage ; (4) chlorite, albite, epi- dote, actinote, chloritoid as general paragenesis of late regional meta- morphism. According to these authors, the first three parageneses cor- respond to two metamorphic events ; the high temperature and low pressure paragenesis (3) shows limited extension within the area of paragenesis (2), where it forms by substituting paragenesis (1). Conco- mitantly with parageneses (2) and (3) took place the regional migma- tisation subordinately accompanied by palingenetic magmas at present- day erosion levels. Except for migmatisation on wide areas of para- genesis (2) of barroviân type, it is to note a similar metamorphic history of Rebra Group and Sebeș-Lotru Group. However, it is worth mention- ing that the rocks of the Rebra Group from Preluca Lăpușului exhibit a general reorganization of the paragenesis including staurolite, kyanite, without any important mineralogical transformations, posterior to strong deformation (Balintoni, 1982, unpublished data). Because of limited space we present no other Precambrian piles. Further on, their general characteristics are treated upon. The Precambrian formations do not exhibit inner unconformities, their outcropping lower parts resting on tectonic planes. Institutul Geologic al României IGR/ 12 I. BALINTONI 6 General Characteristics of pre-Alpine Carpathian Metamorphics 1. The Hercynian metamorphics exhibit a sole general paragenesis, the Early Caledonian ones two and the Precambrian ones two or three. That is to say that pre-Hercynian metamorphics are polymetamorphic and to one orogenesis may be assigned only one general paragenesis. Thus, the instances from the Carpathians decrease the importance of multi-stage metamorphism model and plead for a polycyclic one. 2. Obvious zonations have been reported so far for the second general paragenesis of Precambrian metamorphics (Bercia, 1975 ; Hârto- panu, 1982). It means that the inițial general parageneses were not zoned for any of pre-Alpine Carpathian metamorphics piles. In the past, isogrades were stated between the index minerals of different general parageneses. 3. The Hercynian general paragenesis belongs to the chlorite zone both of super- and infrastructures, where it formed from top to bottom to the limit reached by water. The inițial general paragenesis of Pre- cambrian metamorphics is of low pressure type in places of high tem- perature (andalusite, cordierite, sillimanite) and in case it formed during Early Caledonian orogeny (this could be accounted for by the fact that the general paragenesis of Early Caledonian metamorphics formed under static conditions). then it differs thermodynamically from the latter. 4. Precambrian metamorphics alone exhibit autochthonous grani- tizations associated with extended migmatisation, as well as regional migmatisations independent of granitoids. This accounts on the one hand for the deep erosion of Precambrian metamorphics, and on the other hand for their great thickness, opposed to the film-like aspect of most Hercynian metamorphics. 5. As regards some Precambrian metamorphics with only two general parageneses, a regional migmatisation posterior to inițial meta- morphism was revealed. 6. No high pressure paragenesis has been reported so far for the pre-Alpine metamorphics in the Romanian Carpathians. 7. The thickness of metamorphics decreases obviously from Pre- cambrian to Hercynian ones. This characteristic is accompanied by the decrease of intensity of metamorphism. As compared to the above men- tioned characteristics, the metamorphics which have not been assigned to the orogenies in which they were classified (most of the Tibău Series and the Argestru Series in the East Carpathians, the Arada Formation, the Codru Complex and the Muncel Formation in the Apuseni Mts, the Nădrag Series, the Bătrîna Series, the Ghelar and Govăjdia Series in Southern facies and the Lerești Formation in the South Carpathians) are Precambrian in age. Physical Features of Metamorphic Processes 1. The examples given above show that repeated metamorphic processes lead to mineralogical changes of pre-existing metamorphics in case : the baric field alters within a mineral association the equilibrium of which depends on pressure at a given temperature ; fluids or magmas, Institutul Geologic al României \ IGR7 POLYMETAMORPHISM IN THE ROMANIAN CARPATHIANS 13 independently of their movement direction, enter another thermody- namic field than the one in which the pre-existing metamorphics were generated ; the crystalline networks of pre-existing minerals become deformationally unstable with great rock volumes and a thermodynamic field characteristic of the metamorphic domain. 2. The pre-existing metamorphics are not always proved to have been retromorphosed as infrastructures of some sedimentary or volcano- sedimentary sequences. 3. For some general parageneses one may state high grade cystal- lization conditions, even in the absence of some minerals such as stau- rolite or aluminium silicates, on the condition that chlorite be lacking ; the absence of the latter from a general paragenesis where it may be chemically present, points to a zone above the almandine zone, namely the staurolite zone. The inițial metamorphism of all Carpathian Pre- cambrian metamorphics enters the present-day erosion level of chlorite- out field. 4. Some Precambrian piles exhibit eologites. As compared to the inițial general paragenesis they show relief features. 5. Hercynian metamorphics and probably a part of the Cibin Group (Krăutner et al., 1983 a) overlie a sialic basement. By considering the Alpine metamorphics, such instances are related to overthrust fields in collision areas between sialic plates. Pre-Alpine Metamorphics and Global Tectonics We note the following : Hercynian nappes are known on the Car- pathian territory (Balintoni et al., 1983, Berza et al., 1983) ; pre-Alpine high pressure metamorphics are not known, but one encounters pre- Alpine low pressure parageneses as well as Cadomian, Early Caledonian and Hercynian granitoids within delimited areas that point to certain alignments ; metamorphosed sequences overlie a sialic basement or represent thick sialic piles ; there are also some alignments delimited by pre-Alpine ophiolites. All these remarks account for different meta- morphic processes related to converging contacts between crustal plates, ended by collisions, starting from Cadomian to Hercynian times. Owing to their characteristics, most of Carpathian pre-Alpine metamorphics represent sequences of the compartment situated above the Wadati- Benioff plane. REFERENCES Balintoni I., Chițimuș V. (1973) Prezența paramorfozelor de rutil după brookit în cristalinul seriei de Tulgheș (Carpații Orientali). St. cerc. geol., geofiz. geogr., Geol., 18, 2, 329—334, București. — Gheuca I. (1977) Metamorfism progresiv, metamorfism regresiv și tectonică în regiunea Zugreni-Barnar (Carpații Orientali). D. S. Inst. geol. geofiz., LXIII/5, 11—38, București. 14 I. BALINTONI 8 — (in press) Contributions to the Knowledge of the Metamorphic History of the Argestru Series Rocks in the Puciosul Brook (East Carpathians). D. S. Inst. geol. geofiz., LXIX/1, București. — Gheuca I., Vodă AI. (1983) Alpine and Hercynian Overthrust Nappes from Central and Southern Areas of the East Carpathian Crystalline-Mesozoic Zone. An. Inst. geol. geofiz., LX, 15—22, București. — (1984) Structure of the Right Side of the Bistrița River Between Ciocănești and Vatra Dornei. D. S. Inst. geol. geofiz., LXVIII/5, București. — (in press) Correlation des unites lithostratigraphiques et tectoniques longeant le ruisseau d'Arieș entre la Vallee de Ierii et le Mont Găina (Monts Apu- seni). D. S. Inst. geol. geofiz., LXIX/5, București. — (in press) Aspecte petrologice și tectonice în masivul cristalin Highiș-Drocea (Munții Apuseni). D. S. Inst. geol. geofiz-, București. Bercia I. (1975) Metamorfitele din partea centrală și de sud a Masivului Godeanu. St. tehn. econ., 1/12, 159 p., București. Berza T., Krăutner H. G., Dimitrescu R. (1983) Nappe Structure in the Danubian Window of the Central South Carpathians. An. Inst. geol. geofiz., LX, 31—39, București. Dimitrescu R. (1983) Apuseni Mountains. In : Precambrian in European Variscan and Alpine Belts. Ed. V. Zoubek (in press). Gheuca I-, Dinică I. (in press) Litostratigrafia și tectonica cristalinului Leaotei între Albești-valea Ghimbav-valea Bădeanca (Ezer-Leaota). D. S. Inst. geol. geofiz., București. Giușcă D. (1979) Masivul cristalin al Highișului. St. cerc. geol., geofiz., geogr., Geol., 24, 15—43, București. Hârtopanu I. (1982) Semnificația rocilor cu minerale AL_>SiOr, (disten, andaluzit, sillimanit) în cristalinul Carpaților Meridionali. Thesis of doctor’s degree, 122 p., Univ. București. — Hârtopanu P., Balintoni L, Borcoș M., Rusu A-, Lupu M. (1982) Harta geo- logică a României, scara 1 :50.000, Foaia Valea Ierii. Arch. of the Inst. Geol. Geophys., București. lancu V. (in press) Metamorphism and J-ieformation — Further Indicators in Establishing of the Lithostratigraphic Succession of Some Polycyclic For- mations. D. S. Inst. geol. geofiz., LXIX/5, București. Iliescu V., Krăutner H. G-, Krăutner FI., Hann H. (1983) New Palynological Proofs on the Cambrian Age of the Tulgheș Group (East Carpathians). An. Inst. geol. geofiz., LIX, 7—17, București. Krăutner H. G. (1980) Lithostratigraphic Correlation of the Precambrian of the Romanian Carpathians. An. Inst. geol. geofiz., LVII, 229—296, București. — (1980) East Carpathians. In : Precambrian in European Variscan and Alpine Belts. Ed. V. Zoubek (in press). — Berza T., Dimitrescu R. (1983 a) South Carpathians. In : Precambrian in European Variscan and Alpine Belts. Ed. V. Zoubek (in press). — Berza T., Hârtopanu I., Mureșan M. (1983 b) Precambrian in the South and East Carpathians. Guidebook „Problemnaia komisia IX, MS AN SS, Meeting of the Working Groups 1.1. and 1.2. Inst. geol. geofiz., București. — Năstăseanu S., Berza T., Stănoiu I., lancu V. (1981) Metamorphosed Paleozoic in the South Carpathians and its Relations with the pre-Paleozoic Basement. Institutul Geologic al României / 9 POLYMETAMORPHISM IN THE ROMANIAN CARPATHIANS 15 Carp.-Balk. Geol. Assoc., 12th Congr., Guide to Excursion Al, 116 p., București. Miyashiro A. (1975) Metamorphism and Metamorphic Belts. 479 p., George Allen & Unwin LTD, London. Rădulescu D., Dimitrescu R. (1982) Petrologia endogenă a teritoriului R. S. Ro- mânia. Univ. București. Salop I. L. (1983) Geological Evolution of the Earth During the Precambrian. 459 p, Springer-Verlag, Berlin. Săndulescu M., Krăutner H. G-, Balintoni I., Russo-Săndulescu D., Micu M. (1981) The Structure of the East Carpathians (Moldavia-Maramureș Area). Carp.- Balk. Geol. Assoc., 12th Congr., Guide to Excursion Bl, 92 p., București. Solomon I., Moțoi Gr., Moțoi A., Mărgărit M., Mărgărit G. (1984) Cercetări geo- logice pe versantul estic al Munților Gilău (Munții Apuseni). D. S. Inst. geol. geofiz., LXVIII/5, București. Turner F. I. (1968) Metamorphic Geology. 403 p., Ed. Mc Graw Hill, New York. Vernon H. R. (1976) Metamorphic Processes, Reactions and Microstructure Deve- lopment. 246 p., George Allen & Unwin LTD, London. Visarion A. (1970) Asupra prezenței unei asociații microfloristice în seria de Muncel (Munții Bihor). D. S. Inst. geol. LV/3, 227—229, București. — Dimitrescu R. (1971) Contribuțiuni la determinarea vârstei unor șisturi cris- taline din Munții Apuseni. Anal. șt. Univ. „Al. I. Cuza“, Secț. II, b, Geol. , XVIII, 1—13, Iași. Winkler H. G. F. (1976) Petrogenesis of Metamorphic Rocks. 334 p., Springer- Verlag, Berlin. .3 Institutul Geologic al României XJGRZ Institutul Geological României Petrologie-Mineralogie CURVES OF MINERAL ISORELATIONS, A CONCRETE METHOD TO RESEARCH METAMORPHISM CONDITIONS BY IOSIF BERCIA *. ION HÂRTOPANU MARIN ȘECLĂMAN 2 Introduction The assessment of physical conditions of metamorphism in various areas is usually obtained by tracing the isograde eurves with the help of index minerals. This method was used for a long time in the Car- pathian areas. In mose cases, anyhow, it appeared that assemblages con- taining index minerals are in an evident Chemical unbalance, taking into consideration the fact that the numberof real phasesoften exceeds by the one foreseen by the mineralogical phases rule. More than that, the micro- scopical observations on reciprocal relationships among the minerals com- posing these complex assemblages show a clear paragenetic superposition as some minerals are relict and others of neoformation. Even the index minerals which are classic have either relict or neoformation appear- ances. Having in view these considerations, we think that the isograde lines traced now on the map refer to heterogeneous events and con- ditions ; they mask the real physical conditions from the climax period of metamorphism. Taking into account this difficulty, we agree to another alternative of studying the mineral assemblage. The main idea is : by microscopical analyses we underline for each area the relict and the neoformation minerals and when considering them, we delimit the mineral reaction of adaptation which took place in the respective area. The area outline where the same type of relationship took place is shown on the map as a line which we denominate as the mineral iso- relation curve. Thus, instead of isogrades which should have designated the same metamorphism conditions (usually equiliibrium monovarying conditions of metamorphism), within the metamorphic space, some mineral isorelation eurves are traced, which separate geological spaces with different mineral reactions. In this way, we think a better obser- vation basis can be outlined, in order to understand the evolution sense of variable conditions of metamorphism. 2 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 2 University of Bucharest, Faculty of Geology and Geography, Bd. N. Băl- cescu 1, București. 2 - c. 667 Institutul Geologic al României IGR/ 18 I. BERCIA et al. Reaction Identification The mineral reactions are practically identified under microscope, by following the space relationships among them. This method has been used for a long time but it needs a caretul precaution, because : — a thin section not always detects a whole minerali reaction ; — the Chemical composition of many metamorphic minerals is variable, as for the isomorphous series, so that it is often difficult to delimit the chemism of the reaction terms. For this reason we are often obliged to attribute a standard composition to many minerals with a variable chemism ; — the relative age of minerals is sometimes ambiguous and thus the old reaction term cannot be separated from the neoformed one. It is also to be understood that a mineral reaction can be really “read” under microscope only where the reactions were incomplete, namely only where some transition States were preserved from the inițial reaction member to the final one. Under microscope, the minerals belonging to the inițial reaction term are metasomatically replaced by the minerals of the second reaction members. A reaction is completely established (“read”) when there appear some coupled substitutions, such as : a) A substituted by B ; b) C substituted by D, arud when the general chemism of the assemblage A -f- C is the same as the general chemism of the assemblage B D. In this case, the real and complete mineral reaction is the following : A + C------->B + D Taken as a whole, this is an isochemical mineral reaction, but when regarded at a crystal scale, it is expressed as a metasomatic substitution. In most cases, by direct observations in the same thin section only a side of the substitution couple is remarked. For example, only the substitution of A by B is evident, while the substitution relationship of C by D is absent. The causes can be different, but the most frequent one seems to be the relative amount of reacting minerals. If the com- plete reaction supposes : a A + cC------------------------------> bB 4- dD where a, c, b and d are stoechiometric coefficients and if within the inițial assemblage the relative amount of A is larger as compared to the coefficient a asked by the reaction, the final result of the reaction would be : A + C------> B D A (in excess) In this case, the inițial phase A survives as a relict, coexisting with the reaction products B and D. In exchange, the phase C com- pletely disappears and is going to be deduced. Anyway, it is known! that in each metamorphic area the relative ratios among minerals from an assemblage vary from one point to another, so that if in a certain space from the metamorphic area it is an excess of A, it is possible that in another space to be an excess of C, the latter surviving Institutul Geologic al României 3 MINERAL ISORELATIONS AND THE METAMORPHISM CONDITIONS 19 as a relief. In this case, for each space separately, we ”read“ in thin sections only parțial reactions : A -|- x -> B + y or C + x -* D + y- Here x is the old mineral which disappeared or which is not seen under microscope in a relationship of substitution with one of the neo- formation minerals. Such reactions, with a hidden term (x), which is going to be deduced, are called cryptical. Isorelation in the South Carpathians The question of replacing metamorphism isogrades by mineral iso- relation curves was recently discussed by Hârtopanu (1982) who traced this kind of curves in the Mehedinți Mts ; they were traced as well in the Godeanu Mts by the authors of the present paper (Figs. la and b). Fig. la — Mineral isorela- tion curves in the crystalline of the Bahna Outlier (scale 1 :200 000). Substitution relationships. 1, biotite gârneț ; 2, staurolite' andalusite : 3, biotite andalu- site ; 4, kyanite muscovite. Fig. 1b — Mineral isorelation curves in the crystalline of the Godeanu Mts. Substitution relationships. 1, kyanite muscovite ; 2, stauro- lite andalusite ; 3, biotite/ gârneț. Institutul Geological României 20 I. BERCIA et al. Each isorelation curve delimits an area in which a certain type of cryptical mineral reaction was found. Here below we give the main lines : 1) The staurolite-andalusite isorelation line. This one separates the area with a clear substitution of andalusite by staurolite ; it corresponds to the following cryptical reaction : staurolite + x-----> andalusite + y The optical constants of staurolite relicts from andalusite neofor- mation phenoblasts correspond to a Fe-staurolite. The absence of Fe in andalusite makes us suppose that y must be a complementary Fe bearing mineral. The complete mineral reaction is similar to that proposed by Wenk et al. (1974) : 6 Fe2AlsSi4O23 (OH)+11 SiO,= 4 Fe3Al2(SiO4)3+23 Al2SiO5+3 H2O (I) Fe staurolite quartz almandine andalusite 2) Another line outlines the area where kyanite is replaced by muscovite, corresponding to the following cryptical reaction : kyanite x---------> muscovite + y The kyanite substitution by muscovite is easily to remark under microscope. At first sight, it would seem to be a side of the classical regressive reaction : kyanite 4- potassium feldspar 4- H2O ■----> muscovite 4" quartz Anyhow, in most cases there is no sign to indicate the presence of potassium feldspar within the primary assemblage with kyanite. In exchange, the cryptical reaction area is partly superposed over another reaction area, namely : 3) The substitution relationship area of biotite by gârneț (alman- dine), namely the area with biotite relicts in gârneț corresponding to the following cryptical reaction : biotite -j- x---> almandine -j- y It clearly appears that cryptical reactions 2) and 3) are comple- mentary sides of the same iscchemical mineral reaction : Al2SiO5+KFe3AlSi3O10(OH)2+2 SiO2--------->KAl3Si3O10 (OH)2+ ,Țn +Fe3Al2 (SiO4)3--------------------------1 } 4. Another isorelation line outlines the area with an evident substi- tution of biotite by andalusite. The cryptical reaction in this case is : biotite -r x----> andalusite 4- y. By deduction we conclude that this cryptical reaction is the com- plementary side of a complex mineral reaction which implies the simul- taneous participation of reactions (I) and (II) : Institutul Geologica! României 5 MINERAL ISORELATIONS AND THE METAMORPHISM CONDITIONS 21 Thus, by the help of isorelation lines we can conclude that within the same metamorphism space there coexist some terms of two mineral parageneses belonging to two different conditions. The mineral isorelation lines tracing in the Mehedinți and Godeanu mountains (South Carpathians) ends a long research period. In the Godeanu Mts, Bercia (1975) described a Barrovian type metamorphism in the western part of the rnassif and an intermediary type metamorphism of low pressure, in its eastern part. The question whether the two metamorphism types (located in neighbouring, partly superposed areas) are synchronous or in succession, is still unsolved. In the Mehedinți Mts, in the Bahna Outlier area, a Barrovian type metamorphism was described as well, over which there is a partly super- posed Pyrenean type metamorphism (Hârtopanu, 1975). The direct sub- stitution relationships among minerals characteristic for the two types of metamorphism demonstrate their succession in time and therefore the polymetamorphic character of the metamorphic area of the Mehedinți Mts. The isorelation lines underline the polymetamorphism by the point- ing out of the two superposed parageneses, both in the Mehedinți Mts and in the Godeanu Mts. The two parageneses show that the same metamorphic area successively passed from higher pressure conditions to lower pressure ones. Final Remarks The analysis of the structural relationships among minerals is the main way to discover the Chemical reactions and polymorphic trans- formations which took place during the polycyclic metamorphism. Thus, we can distinguish the old minerals (paleominerals) and the new ones (neominerals). The paleominerals survival is probably due to two causes : — the relatively low speed of some complex reactions which implies the participation of many minerals, widespread on a relatively large area. The slow ’diffusion of componenta towards new germs could be the main reason of such a slow reaction ; — the variability of minerals ratio from an assemblage which causes the excess of one or more minerals. The mineral in excess is not entirely consumed and it is preserved as a relief among the other neo- formation minerals. The discovery of paleominerals is sometimes a difficv.lt job which supposes a very careful observation under microscope. But even in this case the microscope can seldom notice relationships among minerals implied in reaction, either because the reaction space is by far larger than the area of a thin section, or because some paleominerals were totally consumed in the metamorphic reaction. The study of mineral relationships on a large metamorphic area, by tracing the isorelation lines compensates this disadvantage. The sketches below exemplify in Institutul Geological României 22 I. BERCIA et al. a better way the proeess by which the iserelation lines help to the discovery of a reaction, taking as a model the following reaction : kyanite + biotite + quartz------>almandine + muscovite Figure 2 shows the inițial paragenesis area (kyanite -f- biotite + quartz), indicating the spaces where kyanite and biotite respectively are in excess. Figure 3 shows the same area after suffering a new meta- morphic proeess. The isorelation line apparently separates two para- geneses : muscovite + gârneț -f- biotite (on the right) and muscovite 4~ + gârneț -j- kyanite (on the left). But the mineral assemblage on the right has biotite as a paleomineral and the assemblage on the left contains kyanite as a paleomineral. Only near the isorelation line the coexistence of the two paleominerals is possible and only here the mineral reaction can be relativeiy eorrectly “read”. Even the mineral reaction kyanite + biotite + quartz muscovite + gârneț, which in our opinion is very widespread in the polymetamorphic areas of many orogene zones, is hardly noticed without the help of isorelation lines. It is true that the tracing of an isorelation line supposes a very hard work. But we think that with the help of these lines, some other- wise unnoticed mineral reactions can be discovered. We also think that the mineral isorelation line has the quality to express in a concrete way a mineral reaction in the field and at the same time the quality to materiailize on the map the statiStical character of the pers- pective reaction. Institutul Geologic al României MINE'RAL ISORELATIONS AND THE METAMORPHISM CONDITIONS 23 REFERENCES Bercia I. (1975) Metamorfitele din partea centrală și de sud a Masivului Godeanu. Stud. tehn. econ., 1/12, București. Hârtopanu I. (1975) Metamorfismul de presiune coborîtă din Munții Mehedinți (peticul de Bahna). D. S. Inst. geol. geofiz., LXI, 217—'238, București. Hârtopanu I. (1982) Semnificația rocilor cu minerale ALSiOs (disten, anidaluzit, sillimanit) în cristalinul Carpaților Meridionali. Thesis of doctor’s degree, Univ. București. Wenk H. R., Wenk E., Wallace J. H. (1974) Metamorphic Mineral Assemblages in Pelitic Rocks of the Bergell Alps. Schweiz. mineral, petrogr. Mitt. 54, 507—554. Institutul Geological României Petrologie-Mineralogie DYNAMIC AND RETROGRADE METAMORPHISM : EXAMPLES FROM THE ROMANIAN SOUTH CARPATHIANS BY TUDOR BERZA VIORICA IANCU *, HORST PETER HANN ANTONETA SEGHEDI 1 Recent progress achieved in the study of the present geological structure and past evolution of the Romanian Carpathians results from a better approach to the metamorphic petrology. Thus, large areas of long time called ”greenschist facies rocks“ have proved to be polymetamorphic, with at least one medium-grade relict paragenesis, variously obliterated by low-grade minerals. More- over, some ”phyllite zones“ sandwiched between gneissic zones are in fact mylonitic or blastomylonitic belts, marking the border between distinct tectonic units. The aim of this paper is to review such key zones in the South Carpathians, familiar to the authors, after a brief discussion of the terminology and genetic models most widely accepted. The State of the Problem Textbooks and review papers generally make a distinction bet- ween elongate zones of highly deformed rocks and large areas of downgraded crystalline schists, by discussing them either in distinct sections, or in independent contributions. However, a simultaneous discussion on the termmology foi' the main processes and products of dynamic and regional metamorphism, from both the points of view of metamorphic petrology and structural geology, is useful. Dynamic metamorphism is a solid state rock transformation in which directed pressure (stress) has the dominant role and correspond- ing important străin is obvious (Harker, 1950 ; Turner, 1968 ;• Winkler, 1976). By tradition, its thermal regime was considered to be low, and the deformation of coarse grained rocks to be of crush type (seismic cataclastic metamorphism), while fine grained rocks show plastic behaviour, flowing along slaty cleavage planes (Harker, 1950 ; Spry, 1969). Recent papers claim for higher temperatures in the deepest- seated segments of some fault zones with consequent involvement of 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. Sr Institutul Geological României \I6R 26 T. BERZA et al. different mechanisms of deformation (aseismic quasiplastic creep — Sibson, 1977). From the beginnings of petrology, regional metamorphism has been regarded as a dynamothermal solid state process, in which both temperatura and various types of pressura play essential roles. Exten- sive retrogressions occur usually due to subsequent distinct oro- genic cycles. Theoretical considerations (Harker, 1950) and a gradational series of resulted rocks may justify the consideration of dynamic metamor- phism as a special case of dynamothermal metamorphism, symmetrical to thermal metamorphism, the opposite end member. However, mapping data reveal distinct outcrop patterns for the products of dynamic meta- morphism — elongate thin belts interpreted as shear zones — and for the products of dynamothermal ”regional“ metamorphism — large areas with a more or less belt-like shape. The terminology used for the products of dynamic metamorphism. is rather unsettled due to gradual variations of physical conditions and distinct mechanical behaviour of various rocks in the same environment. Following (partly) Higgins (1971), and especially Spry (1969) and Sibson (1977), we use the following dassification : Cataclastic rocks (random fabric) incohesive cohesive Rocks with fluxion structura matrix with minor neomine- ralization-re- crystallization matrix with strong neo- mineralization- recrystallization fault breccia — fault gouge protocataclasite-cata- clasite-ultracataclasite protomylonite-mylo- nite-ultramylonite (phyllonite when phyllosilicates are abundant) blastomylonite Cataclastic Rocks in the Olt Valley In the Olt Valley, two orthogonal faults (30—50 km long) dissect both the uppermost Alpine nappes of the South Carpathians and their posttectonic cover : the N-S trending Olt Fault and the E-W trending Cozia Fault, considered synchronous (post-Lower Miocene) by Hann and Szăsz (1984). The Olt Fault is distentional, with the eastern side down-thrown. This fault is marked by both cataclastic (protocataclasites, cataclasites, ultracataclasites, pseudotachylites) and mylonitic rocks, but geomorpho- logic effects are'minor as both walls are built up of similar meta- morphic rocks. The Cozia Fault is also distentional, with the northern side down- thrown, as the posttectonic cover is offset over 1500 m. The contrast DYNAMIC AND RETROGRADE METAMORPHISM 27 between the northern sedimentary wall and the Southern gneissic wall is marked by a steep slope 1000 m high. The dinamically deformed rocks may be seen only in the Southern wall, where extensive cohesive crush breccias are conspicuous. The Southern slope of the Cozia gneissic horst was also affected by extensive cataclasis — the Brezoi Breccia, long time disputed by Romanian geologists whether of tectonic or sedimentary origin. Hann and Szâsz (1981) have pointed out that in this area a sedimentary Senonian breccia comes in contact, in places, with a cohesive crush breccia formed on the Cozia Augengneisses. This crush breccia extends 50 km eastwards and is the result of pre-Senonian tectonics. Most of the faults and fault rocks in the Olt Valley are typical of the elastic-frictional behaviour of brittle rocks, reflecting a shallow (< 10 km) crustal environment (Sibson, 1977). They involve Precam- brian to Senonian rocks, being the result of Neoalpine (Tertiary) tectonics. Cataclasites and Mylonites at the Sole of the Getic Nappe The Getic Nappe is not only the first nappe recognized in the South Carpathians (Murgoci, 1905), but also the most important one as areal extent (15 000 km2), observed thickness (several kms) and minimal horizontal displacement (100 km). Its sole is marked by a layer of dynamically metamorphosed rocks, tens or hundreds of meters thick. described for the first time as mylonites-ultramylonites by Gherasi (1937) in the Godeanu Outlier. The medium-grade polymetamorphic Sebeș-Lotru Group rocks (paragneisses, mica schists, migmatites, amphi- bolites, leptynites, etc.) may show either cataclastic random fabric, or foliated mylonitic fabric (fluxion structure), according to the rock type or to the place of sampling. As a rule, protocataclasites-cataclasites- ultracataclasites derive from quartzo-feldspathic rocks, while mylonites- ultramylonites are found in more mica or amphibole rich rocks. Medium-grade minerals are usually spbject only to physical actions, since biotite, gârneț, hornblende are not frequently chloritized. They occur as more or less eye-shaped porphyroclasts enclosed in a fine grained matrix, mainly resulted from crushing, with extensive recrystal- lization but minor neomineralization. The presence of migmatic veins in paragneisses may produce similar aspects in outcrops, as the quartz- feldspathic ptygmatic layers are boudinated in a mica-rich quasiplastic deformed matrix. The nature and dimensions of the dynamically metamorphosed layer are highly variable, depending both on the angle between the thrust plane and the lithological layering in the crystalline schists of the nappe and on the metamorphic or sedimentary nature, in a given area, of the top of the underlying Danubian Unit. Institutul Geologic al României 28 T. BERZA et a!. 4 Chlorite Blastomylonites in the Culmea Cernei-Vîlcan-Parîng Mountains One of the lowest Alpine nappes in the South Carpathians (the Main Lower Danubian Unit, Berza et al., 1983) exhibits, over a length of 120 km. a thin (~ 1—2 km) strip of blastomylonites, exposed in the Culmea Cernei, Vîlcan and Parîng Mts. The blastomylonites belong to two distinct lithostratigraphic units : Drăgșan Group (amphibolites, lep- tynites, mica gneisses + staurolite + kyanite) with a few associated plutons, to the north ; Lainici-Păiuș Group (quartzites, biotite gneisses, crystalline limestones, graphitic mica gneisses + sillimanite + anda- lusite + cordierite and various types of migmatites) with several asso- ciated granitoid plutons and porphyry diorite dykes, to the south. Medium-grade Precambrian metamorphism, of Barrowian type in the Drăgșan Group and of lower pressure type in the Lainici-Păiuș Group, was first followed by a static regional retrogression, attested by plagio- clase -> epidote + albite, biotite -> chlorite, cordierite -* pinnite. diopside —> tremolite alterations, called “autoretromorphism” by Savu (1970). The boundary zone between Drăgșan and Lainici-Păiuș rocks (or associated granitoids) stands out by the Progressive development, from both directions inwards, of a north dipping penetrative mylonitic folia- tion, deformed in places by centimetric to metric tight kink folds. Medium-grade metamorphic or igneous minerals are more and more distorted. broken and replaced and occur as relict porphyroclasts (mainly feldspars, muscovite and hornblende). Strong neomineralization (albite, chlorite, epidote, tremolite, calcite, fine grained white mica, stilpnomelane) and reerystallization (quartz) do occur and yield to the rocks a blastomylonitic aspect. It is obvious that in this case the dyna- mic metamorphism developed in a thermal regime typical of low-grade metamorphism, in good agreement with the quasiplastic mechanism of deformation inferred from fabric aspects. This blastomylonitic strip is the result of the overthrust of the Drăgșan Group rocks (and associated granitoids) on the Lainici-Păiuș Group rocks, or associated igneous rocks. The relations with various Paleozoic and/or Mesozoic formations in the Vîlcan, Parîng and Rete- zat Mts point, for this thrust, to a surely pre-Alpine (pre-Jurassic. pos- sibly even pre-Namurian) but post-Devonian age (Krăutner et al., 1981). Biotite Blastomylonites in the Mehedinți Plateau In the Porțile de Fier outlier of the Getic Nappe, an old tectonic contact of metamorphic nappe type occurs within the Precambrian Sebeș-Lotru Group rocks (lancu. Hârtopanu, 1932). Underlying the ty- pical Sebeș-Lotru sequences (with polymetamorphism testified by super- imposed generations of mineral parageneses and/or folds), a quartzitic unit (Jidoștița Formation) with specific metamorphic (paragenetic and fabric) features occurs in apparent structural continuity. The transition is marked by a set of common surfaces — S.; in the Sebeș-Lotru rocks (where they obliterate obviously the older S| and S2 planes), S! in the Jidoștița rocks, respectively. Institutul Geological României 5 DYNAMIC AND RETROGRADE METAMORPHISM 29 The increasing density of S3 planes is accompanied by a neomi- neralization in the biotite zone superposed on the kyanite zone mineral association of the Sebeș-Lotru rocks. The latter appear as relict por- phyroclasts (kyanite, plagioclase, muscovite, biotite, hornblende) in a neoformation matrix of quartz, albite-oligoclase, new biotite. These features of the blastomylonites prove that the thermal regime required by the dynamic reorganization of the rocks corresponds to the biotite zone. The nature of the boundary between the two mentioned units is subject to discussion, as it may represent either a metamorphic (biotite zone) overthrust (post S2 for the Sebeș-Lotru Group and post S() for the Jidoștița Formation), or (less probably) an overturned unconformity obliterated by metamorphism (Lancu, Hârtopanu, 1932). Whatever its origin, this plane was subsequentlv folded, therefore the related biotite blastomylonites exhibit a complex outcrop pattern and are locally found within the Sebeș-Lotru sequence. Corbu Gârneț Blastomylonites — Almaj Mountains In the South Almaj Mts a N-S trending shear zone extends over 15 km north of the Danube (Mărunțiu. Seghedi, 1983 a). This shear zone, 300—500 m wide, involves the Plavișevița Gabbros to the west and the polymetamorphic rocks of the Neamțu Group (Upper Precam- brian) — plagioclase gneisses, mica schists, amphibolites, crystalline limestones — to the east. Mylonitisation increases progressively west- wards in the Neamțu Group rocks, towards the tectonic contact with the Plavișevița Gabbros, but usually unaffected rocks grading into highly deformed ones (ultramylonites. phyllonites. blastomylonites) occur even in the most highly deformed area. The rocks of the shear zone underwent intense deformation, recrystallization and neominera- lization. A penetrative mylonitic foliation is dominant in the shear zone, highly obliterating the earlier structural elements. Medium-grade meta- morphic minerals — gârneț, staurolite. sillimanite and andalusite, variously altered to pinnitic aggregates — are deformed and bent in microfold hinges preserved as relics of a previous metamorphic folia- tion ; the porphyroclasts obviously suggest a complex metamorphic history of rocks foredating mylonitisation. The mineral associations in mylonites (muscovite, chlorite, albite, quartz, garnets as minute, idio- blastic or atoli crystals in terrigenous rocks ; albite-epidote-actinolite- chlorite-quartz in amphibolites ; uralite-actinolite-epidote-albite-quartz or actinolite-epidote-quartz in the Plavișevița ”Epigabbros“ and blasto- mylonites respectively) point to gârneț grade temperature prevailing during mylonitisation (Mărunțiu, Seghedi, 1983 b). Field and geochronological evidence suggests a Caledonian age for these deep seated mylonitic processes. In the Cornereva area, the Corbu zone mylonites have been involved in Alpine thrusts (Mărunțiu, Seghedi, 1983 b) ; Alpine deformations resulted in cataclastic rocks with random fabric and thus jA. Institutul Geologic al României 16 R/ 30 T. BERZA et al. 6 polycyclic dynamometamorphosed rocks are common in areas where the Neamțu Group rocks occur. Regional Retrogression in the South Carpathians Excepting the middle part of the pile of Alpine nappes building the South Carpathians (the Getic Nappe respectively), the Precam- brian medium-grade rocks are frequently retrogressed over large areas. In the Supragetic Units, many lithostratigraphic sequences long time described as epizonal have been proved to be polycyclic (Codarcea, 1931 ; Balintoni, 1969 ; Giușcă et al., 1977 ; Hann, Szâsz, 1984 ; lancu, in press ; Gheuca, Dinică, in press). Symmetrically, at the bottom of the nappe pile, some of the Precambrian formations of the basement of the Danu- bian Units were described as polycyclic (Pavelescu, 1953 ; Gherasi, Dimi- trescu, 1969 ; Savu, 1970 ; Bercia, Bercia, 1970 ; Mărunțiu, 1976 ; Gun- nesch. Gunnesch, 1978 ; Berza, Seghedi, 1983). Even in the Getic Nappe — the Borăscu retrogressed zone (Gherasi, 1937) and the North Sebeș Mts retrogressed belt underlying the Cibin Group (Krăutner, 1980) — or in scales at its top (Uria Unit — Hann, Szăsz, 1984) or its sole (Borăscu Unit — Gherasi et al., in press), medium-grade crystalline schists are retrogressed to low-grade associations. The regional retrogression is marked by both the development of low-grade minerals (quartz, albite, chloritie, sericite, tremolite-actinote, stilpnomelane, clinozoizite-epidote, prehnite, calcite, magnetite, pyrite) and superimposed folding, frequently cozonal with the preexistent struc- tures. Index minerals (sillimanite, andalusite, kyanite, staurolite, cor- dierite) or paragenesis, preserved as relict metamorphic porphyroclasts, account for the preexistent metamorphic events of medium or high grade (Barrowian or low-pressure type). On a mesoscopic scale, retro- gressed areas are characterized by the development of new folds and foliations, overpfinting earlier structures. Low-grade superimposed metamorphism is also responsible for an incipient metamorphic differentiation, as testified by quartz + chlor- ite + tremolite + epidote + adular veins. Some authors also claimed its significance as metallogenetic factor, as magnetite (Hann, Szâsz, 1984) and base metal sulphide (Giușcă et al., 1978) concentrations in the Cibin and Făgăraș Mts show paragenetic and structural features common with the retrogressive event. The degree of retrograde regional adaptation is unhomogeneous and diversified : in some areas the retrogression is uncomplete, older minerals and structures coexisting with the new ones, and in other areas the predominance of neoformation minerals associated with new very penetrative foliations lends an obvious greenschist facies appear- ance to the rocks. This type of retrogression was ascribed to regional low-grade Paleozoic (Early Caledonian or Variscan) metamorphism, Pro- gressive in respect to the Paleozoic formations, but regressive as regards the basement (Balintoni, 1969 ; Savu, 1970 ; Berza, 1975 ; Krăutner, 1980 ; lancu, in press). The regionally retrogressed Precambrian sequences were frequently involved in Alpine or pre-Alpine thrusts, locally undergoing additional Institutul Geological României 7 DYNAM1C AND RETROGRADE METAMORPHISM 31 dynamic metamorphism (Uria Formation, Rîușorul Formation, parts of the outcroip ai'ea of the Drăgșan Group, Corbu and Vodna “phyl- lites“, ete.). These areas are difficult to study, but modem devices of metamorphic petrology and structural geology have enabled contem- porary researchers to reconstitute their complex history, thus achieving more realistic structural models of the South Carpathians. REFERENCES Balintoni I. (1969) Asupra caracterului retromorf al paragnaiselor biotitice cu dorit de pe Bîrsa Croșetului (Făgăraș). Bul. Soc. șt. geol. România, XI, 275—281, București. Bercia I., Bercia E. (1980) The Crystalline of the Danubian Domain from the Banat (Romania). Rev. roum. geol., geophys. geogr., Geol., 24, 3—13, București. Berza T. (1975) Seria elastică și cîteva probleme de stratigrafie și metamorfism ale formațiunilor cristalofiliene din partea-»externă a autohtonului danubian (Carpații Meridionali). St. cerc. geol. geofiz., geogr., Geol., 20, 2, 179—186, București. — Krăutner H., Dimitrescu R. (1983) Nappe Structure in the Danubian Window of the Central South Carpathians. An. Inst. geol. geofiz., LX, 31—39, București. — Seghedi A. (1983) The Crystalline Basement of the Danubian Units in the Central South Carpathians : Constitution and Metamorphic History. An. Inst. geol. geofiz., LXII, 15—22, București. Codarcea Al. (1931) Studiu geologic și petrografic al regiunii Ocna de Fier — Bocșa Montană (jud. Caraș-Banat). An. Inst. Geol. Rom., XV, 1—424, București. Gherasi N. (1937) Etude geologique et petrographique dans les Monts Godeanu et Țarcu. An. Inst. Geol. Rom., XIII, p. 1—78. București. — Dimitrescu R. (T969) Contribuțiuni petrotectonice la structura cristalinului danubian în partea nordică a Munților Petreanu și Retezat. An. St. Univ. „Al. I. Cuza“ (serie nouă), Secț. II b, XV, 29—38, Iași. — Berza T., Seghedi A., Stepan M., lancu V. (in press) Structura geologică a părții nordice a masivului Godeanu (Carpații Meridionali). D. S. Inst. geol. geofiz., București. Gheuca I., Dinică I. (in press) Litostratigrafia și tectonica cristalinului Leaotei între Albești-Valea Ghimbav-Valea Bădeanca (lezer-Leaota). D. S. Inst. geol. geofiz., București. Gunnesch K., Gunnesch M. (1978) Formațiunile cristalofiliene din sud-estul Mun- ților Almajului (Banat). St. cerc. geol. geofiz. geogr., Geol., 23/1, București. Giușcă D., Anastasiu N., Popescu Gh. C., Șeclăman M. (1977) Observații asupra șisturilor cristaline din zona centrală a masivului Făgăraș (Cumpăna-Valea Cîrțișoara). Anal. Univ. București, Geol., XXVI, 1—17, București. Hann H. P., Szâsz L. (1981) Originea breciilor din masivul cristalin Cozaa-Năruțiu (Brezoi-Vîlcea, Carpații Meridionali). St. cerc. geol. geofiz. geogr., Geol., 26, 2, 249—263, București. — Szâsz L. (1984) Geological Structure from Olt Valley between Cîineni and Brezoi. D. S. Inst. geol. geofiz., LVIII/5 (1981), București. Institutul Geologic al României 32 T. BERZA et al. 8 Harker A. (1950) Metamorphism. Methuen & Co. Itd., 362 p., London. Higgins M. W. (1971) Cataclastic rocks. Geol. Surv. Prof. Pap. 687, 97 p., Washington. lancu V. (in press) Date noi privind formațiunile metamorfice policiclice din zona Bocșa (Banat). D. S. Inst. geol. geofiz., București. — Hârtopanu I. (1982) Relations entre les formations metamorphiques poly- cycliques du Plateau Mehedinți. D. S. Inst. geol. geofiz., LXVII/5, (1979— 1980), 67—88, București. Krautner H. (1980) Precambrian unconformity in the Getic Nappe (South Car- pathians). An. Inst. geol. geofiz., LVII, 305—324, București. — Năstăseanu S., Berza T., Stănoiu I., lancu V. (1981) Metamorphosed Paleozoic in the South Carpathians and its Relations with the Pre-Paleozoic Basement. Carp.-Balk. Geol. Assoc. 12th Congr., Guide to Excursion Al. București. Mărunțiu M. (1976) Asupra prezenței distenului în metamorfitele seriei de lelova (Banatul de sud). D. S. Inst. geol. geofiz., LVII/1, 245—252, București. — Seghedi A. (1983 a) New Data Concerning the Metamorphic Rocks and Metamorphic Processes in the Eastern Almaj Mountains. Rev. roum. geol., geophys, geogr., Geol., 27, 29—35, București. — Seghedi A. (1983 b) Mylonites in the Almaj Mountains. Anal. Univ. Bucu- rești, Geol., XXXII, 11—17, București. Murgoci (1905) La grande nappe des Carpates Meridionales. Contribution â la tectonique des Carpates Meridionales. C. R. Acad. Paris, 3, VIII, 1905. Pavelescu L. (1953) Studiul geologic și petrografic al regiunii centrale și de SE a Munților Retezat. An. Com. Geol., XXV, 119—210, București. Savu H. (1970) Structura plutonului granitoid de Șușița și relațiile sale cu forma- țiunile autohtonului danubian (Carpații Meridionali). D. S. Inst. geol., LVI, 5, 123—153, București. Sibson R. H. (1977) Fault rocks and fault mechanism. J. Geol. Soc. London, 133, 191—213, London. Spry (1969) Metamorphic textures. Pergamon Press, 350 p., Oxford. Turner F. S. (1968) Metamorphic petrology. Mc.Graw-Hill, 403 p., New York. Winkler H. G. F. (1976) Petrogenesis of Metamorphic Rocks. Springer, 334 p., New York. jA Institutul Geological României IGR/ Petrologie-Mineralogie MINERALOGY OF ALPINE VEINS FROM THE ROMANIAN CARPATHIANS BY EMIL CONSTANTINESCU \ GAVRIL SĂBĂU 2 The Alpine veins, raising interest for their mineralogical and textural peculiarities, are well developed in the Alps (Parker, 1954), the Sudetes (Ansilewski, 1958), the Rhodopes (Kostov, 1965). This paper describes some new occurrances within the Romanian Carpathians. The Alpine veins which were examined consist of some various mineralogical assemblages, being encompassed within different metamorphic rock types. 1. The assemblage: quartz-adularia-chlorite-iapatite-actinolite, with- in migmatites and laminated granites (Parîng Mts : the Jiu Străit, the Gruniu Brook). 2. The assemblage : quartz-chlorite-albite-actinote-calcite-hematite within amphibolites and amphibolic schists (Făgăraș Mts : the Cheia Valley, the Gălășescu Peak, Cîineni). 3. The assemblage: quartz-albite-chlorite-actinolite-epidote + rutile 4. The assemblage : quartz-chlorite-pyrophyllite-paragonite/musco- niu), and paragneisses (Leaota Mts : the Brusture Brook). The assemblage : quartz-chlorite-pyrophyllite-paragonite/musco- vite-chloritoid within chloritoid bearing pyrophyllitic schists (Parîng Mts : Izvorul, Jieț). The Alpine veins are lenticular in form or appear as irregular nests usually transversally oriented as compared to the schistuosity planes and very seldom along schistuosity (Fig. 1). Cavities are partly or rarely almost completely filled up, sometimes exhibiting a zoning structure (Fig. 2). 1 University of Bucharest, Faculty of Geology and Geography, Chair of Mineralogy, Bd. N. Bălcescu 1, Bucharest. 2 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 3 - c. 667 4 yk Institutul Geologic al României \ igr/ 34 E. CONSTANTINESCU, G. SABAU 2: Fig. 1 — Alpine vein “en echelon” with partly unconformable set ting'. (A), partly concordant (B) in migmatites (Parâng). Fig. 2 — Quartz, chloritoid and pyrophyllite vein with zoning structure in the Schela Formation (Parâng), after Popescu (1983) (unpublished data). Institutul Geologic al României 3 MINERALOGY OF ALPINE VEINS-ROMANIAN CARPATHIANS 35 Description of Main Minerals The composing minerals were analysed by a complex mineralogical study in order to find out their morphological aspects, their optical characters and their chemico-structural peculiarities. Quartz is present in all assemblages, quantitatively dominating the other minerals. Quartz crystals can reach remarkable sizes, up to 20 cm long. Its habițus can be columnary — 20/5 cm (Gruniu) or shortly prismatic — 20/15 cm. Faces were identified (1010), (1011), (0111), (3121), (2111), as well as some rare forms (0552), (3031), (0331) (Fig. 3). Face Fig. 3 — Morphology of quartz crystals from Alpine veins (Parîng) (coli. R. Strusiewicz). •combinations are richer (Gruniu) or simpler (Leaota). Crystals are colour- less and glasslike, milky white, smoky or green. Under microscope, some chlorite inclusions, marginally disposed and in parallel to crystal faces (Figs. 4, 5), or fibrous actinote in the crystal mass were noticed within green crystals. In some cases they can show fluid inclusions (Jieț) ; Fig. 4 — Setting of chlorite and actinote inclusions within green- ish quartz (thin sec- tion, N 10 X). Institutul Geological României 36 E. CONSTANTINESCU, G. SABAU 4 here, the temperature of the fluid phase homogenization was measured on these inclusions (150 determinations) ; for formation temperatures there were obtained some values between 160—180°C (Popescu, Constan- tinescu, 1982). Fig. 5 — Assemblage (1) quartz-adularia-ripidolite- apatite (Parîng). Chlorite is the only mineral found together with quartz in alT. assemblages. Its crystal dimensions are between 1 mm and 1 cm. It shows a lamellar habitus and is disposed in radial aggregates (Fig. 6). Its colour varies from yellowish-green to dark green. Taking into account optical properties and the chemico-structural determinations,. the ripidolite and clinochlore could be separated. Ripidolite is characteristical for assemblage 1 (Parîng Mts, the Jiu Strait and the Gruniu Brook) (Fig. 5), where it appears within agglo- Fig. 6 — Chlorite ro- settes associated with quartz and calcite (as- semblage 2) (Făgăraș). Institutul Geological României 5 MINERALOGY OF ALPINE VEINS-ROMANIAN CARPATHIANS 37 merations of crystals with a helminthic structure (Fig. 7), single crystals having a prismatic habitus. It is weakly pleochroic from yellowish to green and its birefringence colour is dark grey, often anomalous with bluish shades. Clinochlore which appears within assemblages 2 and 3 is set out in rosettes with undulose extinction (Fig. 8) or in dispersed isolated crystals. Its pleochroism is more intense with chlorites in assemblage 2 and weaker with those in assemblage 3. Its birefringence Fig. 9 — Thermodif- ferential curve of ripi- dolite (Parîng). Institutul Geologic al României 38 E. CONSTANTINESCU, G. SABAU 6 colours are usually anomalous (yellow-brown, violaceous), rarely normal but very low (dark grey). The precise Identification of mineral species could be carried out by means of RX diffraction, IR spectrography and thermodifferential analyses (Fig. 9). Adularia appears only in assemblage 1 (Parîng Mts, Gruniu) asso- ciated with quartz, ripidolite, apatite (Fig. 3). Its crystals have a shortly Fig. 10 — Morphology of adularia crystals (Parîng). Fig. 11 — Lamellar and diffuse optical non-homogeneities in adularia (thin section, N +, 40 X). prismatic habitus and dimensions between 1—4 cm. Faces are well represented (110), (110), (001), (201), with a larger development of face (201), in prejudice of face (001) (Fig. 10). Twins often appear after Manebach, Baveno and pericline-j-albite laws. Microscopica.! observations have indicated an optical non-homogeneity marked by a variation of the 2V angle, between 67—83° and of the extinction angle CNm between 12—17°, in different crystal zones. There were noticed some zonal structures, both macroscopically by colour variations, and microscopic- ally by the existence of some lamellae having a different optical beha- viour (Fig. 11). Chemical analyses (Tab. 1) allowed the calculation of the structural formula -X3.092 ^^0-245 ®^o.i©o ^^0022 Sin.901 ^^4.427 O32 and the par- Institutul Geologica! României 7 MINERALOGY OF ALPINE VETNS ROMANIAN CARPATHIANS 39 ticipation ratio of final terms from the feldspar group : Fk 89%, Ab 7%, Cs 3%, An 1%. The d/n values and the 1/100 corresponding intensities, calculated according the main diffraction lines are included in Table 1. The tri- clinity calculation has given the value = 0.8 and the sometimes diffuse character of 130 reflexes points out the non-homogeneous character of TABLE 1 Chemical analyses of minerals Alpine veins Minerals Oxidesj Adularia Gruniu, Parîng Mts Pyrophyllitc Jict, Parîng Mts SiO2 TiO2 A12O3 Fe2O3 FeO ' MgO CaO BaO Na«O K2O h2o 64 .20 19 .26 0 .11 0.09 0 .05 0 .12 1 .42 0 .70 13 .04 0 .70 64.19 0.01 28 .77 0 .40 0 .14 0 .16 0.14 0.20 5 .73 99.69 99.74 the adularia from the Alpine veins from the Parîng Mts with monoclinic and triclinic symmetry zones. The main absorption bands in infrared which were obtained on the analysed adularia are characteristic for the stretching frequences Si(Al)-0 (1045 cm'1) ; Si-Al-Si (728 cm-1) and for the deformational fre- quences Si-O-Si (433 cm-1). The value of transmission minimum from 645 cm-1 occupies an intermediary position among characteristical values for sanidine 639 cm-1 and microcline 650 cm-1, indicating an intermediary state of order, as the other bând positions. Albite appears in assemblage 2 and 3 in association with quartz- chlorite-actinote-calcite-hematite, and quartz-chlorite-actinote-epidote respectively. Its crystals are up to 4—6 mm and form monomineral aggregates where only the terminal faces and the prismatic habitus, elongated after the lateral pinacoid (010) can be distinguished. Under microscope it shows a subhedral outline. The determined optical constants : the refraction indexes, the ex- tinction angle and the 2V angle show a content of 5—10% An. While comparing the values of the d/n parameter and those of the 1/100 in- tensity ratio calculated from the RX diffraction analyses which were made in the domain 20: 10—55°, with data obtained by Borg and Smith (1969) there comes out that oui’ values correspond to those obtained for the low albite. Institutul Geological României 40 E. CONSTANTINESCU, G. SABAU This is confirmed by projection of values of wavelengths of absorp- tion bands in IR from domains 18.2—18.9 and 15.3—16.2 on Hafner and Laves’ diagram (1957) which are included in the characteristic low temperature domain. Actinote appears as macroscopieally visible crystals (2—3 mm) in assemblage 2 and 3, associated with quartz-chlorite-albite-calcite or epi- dote, as microscopica! inclusions within quartz and adularia in assem- blage 1 and as asbestiform aggregates (assemblages 2 and 3). Prophyllite appears in assemblage 4 associated with quartz. chlorite and paragonite/muscovite. Its colour is pearly white. In thin sections it appears as scales and elongated leaflets with an anhedral outline, generally having submillimetric dimensions. It is colourless or with a slightly greenish shade. Its birefringence colours vary from grey to greenish-yellow. The extinction angle c^Np = 8—10°. The angle 2V determined in basal sections varies between 54—58°. Its chemical composition is given in Table 1, providing the follow- ing structural formula : K0.031 Na0.033 Ca0>02i (H3O)0.199 Mg0.025 FegJ36 Al3;803 Si7.728Al0 272O20(OH)3.801/24(O)/.The values of interplanar distances deter- mined by RX diffraction are shown in Table 2 and the thermodif- ferential curve in Figure 12. The crystallinity index, considered to be a sensible indicator of phyllosilicate genesis (Dunoyer de Segonzac, 1969) was calculated according the ratio between the height of the peak cor- responding to the (002) reflex and its width at half-hight. The obtained value, —122, is higher for the crystallinity index of pyrophyllite from pyrophyllitic schists —47 (representing the average of five analyses) after Popescu and Constantinescu (1982) and very high as compared to the value obtained for hydrothermal pyrophyllites from Romania —8 (lanovici et al., 1981). Together with the above mentioned minerals, the Alpine veins contam as well some locally spread or quantitatively subordinated minerals : Calcite appears in assemblage 2 as crystals with rhombohedral habitus up to 2 cm with a cleavage perfectly following the colourless Fig. 12 — Thermodifferential curve of pyrophyllite (Parîng). 9 MINERALOGY OF ALBINE VEINS - ROMANIAN CARPATHIANS 41 TABLE 2 din in A tind H10<) values obtained by RX diffraction for minerals of the Alpine nein 1. Adularia 2. Pyrophyllite 3. Ripidolite Nr. d/nA 1/100 Nr. hkl d/nA 1/100 Nr. hkl d/nA 1/10 1 3.93 10 1 002 9 .0544 49.5 1 001 14 .10 10 2 3 .766 15 2 004 4 .5344 7 .2 2 002 7 .08 100 3 3.45 10 3 006 3 .0455 100 3 003 4 .71 10 4 5 3 .29 20 4 132 2.4012 3 4 004 3.54 20 3 .229 100 5 008 2 .2905 10 5 005 2 .82 10 fi 2.985 35 6 0.0.10 1 .8391 22 6 131 .202 2 .59 10 7 2 .889 10 7 1.5289 23 7 132 .202 2 .54 10 8 2 .760 10 8 1 .3799 6 8 132 .203 2.45 15 9 2 .55 25 9 1 .3644 7 9 132 .202 2.38 10 10 2.319 10 10 133.204 2.25 10 11 2.154 10 11 135 .204 2.00 15 12 2.119 10 13 2 .049 10 14 1 .887 45 15 1.795 35 IC 1 .615 10 17 1 .449 15 18 1 .406 10 19 1 .382 10 rhombohedral faces or in masses having a granulai’ aspect, greyish- white in colour. ’ & Epidote. appears as grains or shortly prismatic crystals, sometimes with curved faces (Fig. 13). Hematite appears in assemblage 2 as lamellar crystals, iron-grey coloured, sometimes disposed in aggregates with a radial aspect. Fig. 13 — Epidote and apatite crystals included in adularia (thin (section, N /!, 10 X). Institutul Geologic al României 42 E. CONSTANTINESCU. G. SĂBAU 10 Conclusions The mineralogica! composition of the Alpine veins from the Romanian Carpathians is a simple one and in all the examined assem- blages it is closely related to the mineralogica! composition of the host rocks. The development of certam minerals is controlled by a specificai petrographic environment. Thus, the adularia exclusively appears in gneissic rocks (migmatites, laminated granites) and the pyrophyllite exclusively appears within pyrophyllitic schists. Chlorites, which appear in all assemblages are characterized by the presence of the ferriferous .species (ripidolite) within the Alpine veins of gneissic rocks and of the magnesian species (clinochlore) within the Alpine veins encompassed in amphibolites and amphibolic schists. Hematite appears as well only in veins of the amphibolic schists as it is formed according to iron levigated from amphiboles. These observations, correlated to the parțial depletion of the host rocks in Chemical elements which form the minerals of the Alpine veins, support the idea of the formation of these minerals by lateral secretion processes. The reciprocal relationships among minerals of the Alpine veins which were macroscopically noticed, indicate a depositional succession of these ones, which allows separation within certam veins .(assem- blages 1—3) of an initially alkaline stage, represented by the crystalli- zation of quartz, adularia and albite, followed by a calc-alkaline stage, when actinote and epidote are formed. Two crystalization stages can be •distinguished as well in assemblage 4; a) chloritoid quartz and b) pyro- phyllitie + quartz of lower temperature (Fig. 2). The crystal morphology for quartz and adularia, the chemico- structural characteristics (order-disorder etc.) for albite and adularia, and the values of homogeneity temperatures for fluid inclusions of quartz indicate medium to low temperatures of formation. The mobilization and redeposition of these minerals are associated with the action of metatectical fluids which have circulated through open frac tur es within metamorphic rocks, after their deformation. Therefore, the Alpine type veins represent the final manifestations ■of regional metamorphism processes from the Romanian Carpathians. REFERENCES Ansilewski I. (1958) On Microcline and Triclinic Adularia. from Bialkie Gory Gneisses (Polish Sudeten). Bul. Akad. Pol. Sci., Sci Chim. Geol. Geogr., VI, 10, 275—282, Warsaw. Borg I. Y., Smith D. K. (1968) Calculated Powder Patterns. II. Five Plagioclases. Am. Min., 53, Washington. Brindley G. W., Gillery F. H. (1956) X-ray Identification of Chlorite Species. Am. Min., 41, p. 169. he only the assemblage B is stable and at h < hc only the assemblage A is stable (in the limit case when the geothermal gradient is the same in the whole metamor- cated on a horizontal equilibrium geosurface). But the geothermal phic space, the hc depth on a given vertical corresponds to a point lo- gradient’s inconstancy within the metamorphic area (which is expressed (GR/ Institutul Geological României 48 I. HÂRTOPANU, M. ȘECLĂMAN 4 by the variation of temperature in the horizontal plane) entails the changing of the he depth from one place to another. In Figure 3a one can see that at a higher geothermal gradient (noted by 2), the equili- brium depth is lower (he). In exchange, in Figure 3b, where the mo- novariant equilibrium curve has a negative slope, it is shown that the equilibrium depths diminish as the geothermal gradient increases.. Therefore, where the geothermal gradient changes from one point to another, the equilibrium depths are inscribed on an irregular equili- brium geosurface. In this case, the equilibrium geosurface is turned away from the horizontal ; as the deviation amplitudes are directly pro- porțional to the horizontal geothermal gradients from the metamorphic space (it is to be noted that the equilibrium geosurface is not parallel to the geothermal surfaee). Dynamics of Equilibrium Geosurfaces A lot of observation data show that within one and the same point of the crust the geothermal gradient was modified with time. The variability in time of the geothermal gradient has large conse- quences upon the equilibrium geosurface, determining thus the verti- cal upward or downward shifting of this surfaee, according to the variation sense of the geothermal gradient and to the monovarying curve slope. Figure 4 shows the effect of the geothermal gradient low- ering as a result of the general cooling of the metamorphic system from the metamorphic space. At the inițial gradient, the equilibrium Fig. 4 — Geothermal gra- dient inerease determines a prograde metamorphism for equilibrium curves with po- sitive slope. depth corresponds to hj but by the lowering in time of the geothermal gradient the depth got down to h2. Within the space between h| and h2 the assemblage A becomes metastable and must pass, by reaction, into the assemblage B. Thus, the mineral reactions can take place only within this depth interval which, in the bidimensional space is encom- pased between the old equilibrium geosurface (a fossil geosurface) which passed through ht and the new surfaee (real surfaee) which passes through h2. We agree to caii this space “reacting” (reacting space), taking into account the fact that only in this space a mineral reaction of thermodynamic accomodation to the time variation of the geothermal \ IGR> Institutul Geological României o MINERAL PARAGENESES 49 gradient is possible. As during the geological time geothermal gradients were variable, it is very likely that, in reality, the separating Urnit between the neighbouring metamorphic zones would not be a surface (an isograde plane), but a reacting space having variable thicknesses where some reactions to replace one assemblage to another there took place. The separating limit between the kyanite and the sillimanite zones from the Godeanu and Semenic Mts is a good example to confirm, the real existence of the reacting space. Close to the equilibrium geo- surface of the two zones (to the isograde line) a paragenetic superpo- sition is remarked, showing clear relationships of parțial replacement of the kyanitic assemblage with the sillimanitic assemblage and in- versely, a proof of the two ways oscillation of the geothermal gradient.. Final Remarks It is very important that between the metamorphic zones there- interposes an equilibrium geosurface with monovarying conditions. Any oscillation in time of the caloric fluxes- affect in the first place the space near the equilibrium geosurface which becomes thus a reacting space. The sense of the metamorphic reactions within the reacting space depends not only on the variation sense of the geothermal gra- dient, but also on the mineral origin of reactions. In most cases, the mineral reactions have positive enthropies and reaction volumes and correspond to a positive slope of the equilibrium eurves in T-P dia- grams. In this case, the increase of the geothermal gradient determines. Fig. 5 — Geothermal gra- dient increase determines a retrograde metamorphism for equilibrium eurves with negative slope. in the reacting space a prograde metamorphism (the lower temperature assemblage passes into the higher temperature assemblage) (Fig. 4). But there are some cases when the reaction eurves slopes are negative (e.g. the dehydration reactions at very high pressures or the probable reactions of transformation between andalusite and sillimanite). In these situations the increase of the caloric fluxes determines retromor- phous mineral reactions (Fig. 5) within the reacting space. 4 — c. 667 Institutul Geological României 50 I. HARTOPANU, m. ȘECLAMAN 6 REFERENCES Bercia I. (1975) Metamorfitele din partea centrală și de sud a masivului Godeanu. Stud. tehn. econ., 1/12, București Miyashiro A. (1973) Paired and Unpaired Metamorphic Belts. Tectonophysics, 17 (3), 241—254. Savu H. (1970) Stratigrafia și izogradele de metamorfism din provincia metamor- fică prebaicaliană din munții Semenic. An. Inst. geol., XXXVIII, București. Tilley C. E. (1925) Metamorphic Zones in the Southern Highlands of Scotland. Geol. Soc. London Quart. J., 81, 100—112, London. Institutul Geologic al României Petrologie-Mineralogie COMPLEX CRITERIA OF SEPARATING WEAKLY METAMORPHOSED FORMATIONS. AN EXAMPLE : THE SOUTH CARPATHIANS BY VIORICA IANCU1, GHEORGHE UDUBAȘA1, SILVIU RĂDAN1, ADINA VISARION1 The present paper deals with some lithosti'atigraphical entities which were affected by a low grade metamorphism and which could be well individualized within the Paleozoic-Mesozoic succesion from the Mehedinți-Retezat Danubian Unit (Stănoiu, 1973) of the South Carpa- thians (Fig. 1). These paleontologically dated entities point out the effects induced by deformation and metamorphism and constitute some guide marks to clear up the lithostratigraphy of the Paleo-Mesozoic metamorphosed formations. The lithosti'atigraphical separation of weakly metamorphosed for- mations from the Carpathian Orogene area implies some hard difficulties caused both by the discontinuous development on a Precambrian base- ment reactivated during the Paleozoic, and by the non-homogeneity of the deformation and metamorphic idegree within the Alpine structures. The areas with a Progressive, orogenic, low grade metamorphism are isolated and point out some non-homogeneities and discontinuities during the same phase. At the same time, some formations show clear effects of overlapping folding (either polyphasic or polycyclic) some- times accompanied by a parțial mineralogical reorganization or by shearing due to overthrusts. Taking into consideration the complex character of the implied phenomena, the synchronous formations can show a different deforma- tional and metamorphic evolution and therefore some different struc- tural-mineralogical aspects. At the same time, some differently aged formations (either Paleozoic or Mesozoic) but with a similar premeta- morphic lithology, can get, by metamorphism and deformation, some convergent structural-petrographic aspects. 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 4 M Institutul Geologic al României xiGșy 52 V. IANCU et al. 2 Fig. 1 — Geological sketch of the Vîlcan Mts (South Carpathians). 1, posULaramian cover ; 2, a, non-differentiated Paleo-Mesozoic cover (post-Ordovician-Silurian) ; b, Upper Paleozoic for- mations ; c, Lias formations with anthracite and metamorphic minerals (chloritoid, pyropyllite, graphite) ; 3, Low®r Paleozoic formaions ; 4, Precambriar basement; 5, overthrusting line; 6, pre-Alpine tectonical line. Institutul Geologic al României ;3 CRITERIA OF SEPARATING WEAKLY METAMORPHOSED FORMATIONS 53 These aspects explain why some Paleozoic and Mesozoic rock se- quences were considered together as being unitary in time and space (e.g. the “Tulișa Series”, the “Schela Formation”, etc.). As the subject of our paper is not a re Vision of the existing stratigraphical schemes and of the evolution in the terminology used for Paleo-Mesozoic formations, we shall deal with the low grade meta- morphic formations which have paleontological dating. 1. Stratigraphical Criteria Among the known and applied stratigraphical criteria for indi- vidualizing lithostratigraphical entities, we must mentibn : — the facies unit and the establishment of lithostratigraphical successions and of real thicknesses (mainly within multistratified se- quences) as compared to the inițial stratification (So), which in most cases is modified or blurred by deformations, sometimes superposed. — the paleontologica! and micropaleontological content. When there are some evident variations in the same main struc- tural imit, it is necessary to follow the facies variations, the inițial thicknesses and the areas with visible effects of orogenic compression (by folding) accompanied by a mineralogical reorganization under stress conditions. This paper deals with some formations with low grade metamor- phism of Paleo-Mesozoic age. 1.1. Lower Paleozoic Within the Lower Paleozoic (pre-Devonian), the Valea Izvorului and Coarnele formations were lithologically individualized and paleon- tologically dated (Stănoiu, 1976). Lithologically, they consist of a lower, mainly quartzitic member and of an upper, mainly schistous member (chloritous + sericitic + quartzous schists with lenticular intercalations of graphitic schists and limestones). The Valea Izvorului Formation has supplied a tabulata fauna (fa- vositins and halisitids), tetracorals, bryozoans (fenestelids), brachiopods, trilobites (Flexicalymene sp., Encrinus sp. or Cromus sp.) and crinoids (Caleidocrinus artifex) which belong to the interval Ordovician-Lower Silurian (Stănoiu, 1976). From both formations, Iliescu (in Stănoiu, Iliescu, 1976) and Vi- sarion have determined a palyno-protistological association with acri- tarches “scolecodonts” and microspores of Ordovician-?Silurian type. Within the rocks belonging to the Coarnele Formation, Visarion (in So- lomon et al., 1976) quotes some spores within the Middle Cambrian- Ordovician. 1.2. Upper Paleozoic There are some continental, detrital formations representing the Variscan molasse facies attributed by Stănoiu and Lejal Nicol (in press) Institutul Geologic al României 54 V. IANCU et al. 4 to the Westphalian-Autunian interval by reconsidering a flora assem- blage previously attributed to the Upper Devonian (Stănoiu. 1976). There were separated (Stănoiu, Lejal-Nicol, in press) : the Valea de' Brazi Formation with Westphalian plant remains and the Culmea Bra- dului Formation which was attributed to the Autunian because of its stratigraphical superposition and of its facial similarity with some other zone formations. The Valea Ide Brazi Formation (Westphalian-Saephanian) is well represented in the eaștern part of the Retezat Mts ; it is about 50—100 m thick and it consiste of sericito-graphitic metapelites, metapsammites and metapsephites. Some spores characteristical for the Upper Carboni- ferous (Florinites sp., Endosporites sp., Alisporites sp., Potoneisporites sp.) together with Devonian spores (probably reworked) were identified by Visarion within the rocks of this formation. The. Culmea Bradului Formation (Autunian) is formed of meta- psephites. metapsammites and reddish or grey metapelites, associated with acidic metavolcanics. 1.3. Mesozoic For the purpose of this paper only certain Mesozoic formations were selected, i.e. those showing a low metamorphic grade with unre- liable paleontological remnants ; they can be hardly separated from the- similarly featured Paleozoic formations. Within the formation of the Jurassic-Lower Cretaceous sedimen- tary cycle the Schela Formation (Manolescu, 1932) has been separated, i.e. a Lias formation of the Gresten type facies. On the largest outcropping area of the Mehedinți-Retezat Unit, the Lias formation mainly contains psammo-psephitic deposits with a maximum stratigraphic thickness of about 50 m. A pelitic-psammitic facies, characterized by the presence of carbonaceous matter (anthra- cite) is developing in some allochthonous units (northern border of the Vîican and Parîng Mts and Southern border of the Vîlcan Mts, Schela zone). Here, there were identified some Lias plants (Manolescu, 1937 ; Semaka, 1963 ; Stănoiu, 1982). 2. Petrological Criteria The petrological criteria utilized by us are : 1) the petrographic and mineralogical assemiblages, 2) the identification of metamorphic neoformation parageneses and 3) their correlatibn to some differentiated structural elements. More specialized studies were made concerning clay and opaque minerals, which can bring some indications about the way and the degree of metamorphic adaptation. According to the above mentioned criteria, there were obtained some conclusive and convergent data for the previously presented for- mations. Other Paleozoic and Mesozoic low grade metamorphic formations do not have unequivocal datings which makes difficult the time loca- Institutul Geologic al României \IGRZ 15 CRITERIA OF SEPARATING WEAKLY METAMORPHOSED FORMATIONS tion of metamorphic events (e.g. the Oslea Formation, the Tusu For- ma tion pro parte, ete.). 2.1. Lower Paleozoic The rocks of the Valea Izvorului and Coarnele formations show a synmetamorphic penetrative foliation accompanied by stable minerals in the chlorite zone of the greenschist facies. The metamorphic neo- dormation minerals oriented in the St plane are the following : sericite (illite), quartz, chlorite, albite, tourmaline, rutile. The pre-metamorphic .sedimentary structures and the bedding (S()) are obliterated by the metamorphic paragenesis, mainly within the Coarnele Formation. The Valea Izvorului fossiliferous Formation is less adapted to metamorphism (from the mineralogical point of view) and preserves more pre-meta- morphic minerals. X-ray data give a simpler assemblage of clay minerals : illite, chlorite. The abundanee of chlorite is remarkable as compared to the other low grade metamorphic formations. The crystallochemical para- meters of illite indicates a very good crystallinity, but associated to a variable ratio of intensity for reflexes 002/001. The chlorite parameters show a more ferriferous term. Reflected light microscopy study of some polished sections showed the presence of rutile and g'raphite ; the latter shows a slightly va- riable optics and exhibits a plastic blehaviour. The carbonaceous matter is lacking ; it is typical for the Lias formation only. The deformations on mesoscopic scale in the Lower Paleozoic rocks are dominated by a general, very penetrative foliation (S^ accom- panied by a prograde mineral assemblage. The Precambrian basement synchronously underwent a retrograde adaptation which can be attri- buted to a late Caledonian phase. 2.2. Upper Paleozoic The Valea de Brazi and Culmea Bradului Upper Paleozoic forma- tions show simple microscopic deformations marked by decimetric to metric folds which affect a unique foliation (S^ within the coarse .grained rock sequences. This foliation is marked by the strong flat- tening — within the bedding plane (So) — of the polygenous elements from metaconglomerates. The matrix is metamorphically partly reor- ganized. The associated microfolds which are often asymmetrical and flat- tened show overtumed axial planes, marked by penetrating plane-axial cleavages within finer, interstratified sequences. These features suggest a superposed folding. The fine, metapelitic sequences show a “slate-like” cleavage, rarely with microfolds preserving bedding (So), and incipient transpositions of this one after Si. Graded bedding are sometimes pre- served within multistratified sequences. The assemblages contam pre- metamorphic minerals and metamorphic neoformation minerals (illite, ■quartz, chlorite, rutile, graphite) which are quantitatively subordinated. Institutul Geologic al României k igr/ 56 V. IANCU et al. & The prevalente of sedimentary mineral assemblages, the small amount of neoformation minerals associated with superficial folds (specificai to the upper structural level) separate them both from the Lower Paleozoie formations and from the Mesozoic ones (mainly the Lias ones), suggest- ing the effects of a late Variscan deformation. 2.3. Mesozoic The Lias formation (Schela) show mixed assemblages formed of pre-metamorphic minerals (sedimentary relicts — either elastic, re- worked from the basement, or formed in the sedimentary environment or by diagenesis) and metamorphic neoformation minerals. The most frequent elastic minerals are : quartz, feldspars, micas (muscovite, bio- tite), tourmaline. These minerals are distinctly dominating within coarse' rocks (metapsephites, metapsammites) and have visible effects of intra- crystalline deformation. Metamorphic reorganizing of the matrix can partly be observed in the bedding plane. The sedimentary and diage- netic minerals are dominant within metapelitic and metasilty rock sequences ; under conditions of orogene metamorphism these rocks are' mineralogically more intensely adapted and structurally featured after- maximum stress directions. The clay minerals of the Lias formation give the possibiiity to follow the transition phases from the burial diagenesis to metamorphism. The Lias formation is characterized by a wide mineralogical variability of the argillaceous fraction, although illite is predominant. All samples contain small amounts of kaolinite (a sedimentary “residual” mineral)' and a lot of samples contain chlorite-vermiculite (a mixed-layer reflect- ing a transition to metamorphism). Illites have a wide variation domain of crystallinity indexes (Kubler, 1967). The ratios of intensity for re- flexes 002/001 have a relatively narrow variation interval with a ten- dency to concentrate values within the aluminous illite domain (Fig. 2a), which allow a direct correlation with the metamorphic degree. The chlorites of the Lias formation have a variable ratio Fe/Mg which could suggest some Progressive crystallo-chemical modifications con- nected to the metamorphism intensity (Fig. 2b). The variation domain of the relatively wide crystallinity index can be the result of an incomplete and selective adaptation, when some minerals specificai to metamorphism (chloritoid, pyrophyllite) have a high frequency within the Lias formation. The microscopic observations have pointed out the mineralogical heterogeneity of petrographic as- semblages (at a thin section level). Microstructura! data underline an incomplete mineralogical restructuration and a “step by step” crystal- lization with static and dynamic phases. Chloritoid appears as rosettes and well individualized crystals, then slightly flattened and penetrated, suggesting a static crystallization before orogene compression deforma- tions. This can be the result of a quick growing of lithostatic pressure in a pre-kinematic “orogene burial” phase (lancu, unpublished data). The continuation of the mineralogical neoformation under dynamic conditions is underlined by synkinematically crystallized minerals (pyro- Institutul Geological României IGRZ '7 CRITERIA OF SEPARATING WEAKLY METAMORPHOSED FORMATIONS 57 phyllite, high cristallinity illite, quartz) in the S| foliation which is plane-axial and associated to mesoscopic folds (B,). The S| foliation is then affected by shear cleavages (S2) ; the chloritoid is sometimes occurring as lens-shaped aggregates between S( and S2 planes (Fig. 3). Fig. 2 — Relationships between crystallinity o£ illites and intensity ra- tio of reflexes 002 001 (a) ; crystallo-chemical characterization ot chlorites (b). 1, Lias formation ; 2, Coarnele Formation. Microscopic aspects ol' the rocks of the Schela Formation (Lias). A detailed study concerning the carbonaceous matter has pointed out the same transition and gradual adaptation of the carbonaceous matter from brittle anthracite (Fig. 4) to graphite through the inter- mediary stages of meta-anthracite and pre-graphite. The carbonaceous fragments have variable (morphological and optical) aspects, connected 58 V. IANCU et al. 8'. with their association to other minerals and with their position as compared to the St plane. Some frequently homogenized petrographie components of anthracite (vitrinite. fusinite) can be found within thicker bands as well. Even in these cases, the colour type of bire- flexion and anisotropy corresponds to graphite ; the diffraction peak Fig. 3 — Pre-S, chlo- ritoi 0.75 (with spacings 10.9—11.9 A by glycolation) can be used to obtain the junction factor and in the conditions PMM — Pmhm = 0 it is obtained a junction factor g higher than 0 (1 or 2). Threecomponent Mixed-Layer Minerals About 10% from the random mixed-layer minerals from the Har- ghita Mts are threecomponent : they are formed mostly of hydromica, subordinately montomorillonite and chlorite. Figure (b, c and d) shows diffractograms of three threecomponent mixed-layer minerals. Institutul Geological României 5 INTERSTRATIFiED CLAY MINERALS—HARGHITA MO O NT A INS 65 In order to study the structure of these random mixed-layer mi- nerals, Weaver’s method (1955) was used to reduce them to two two- component Systems 10—14 A (hydromica-montomorillonite + chlorite, and hydromica + dehydrated montmorillonite-chlorite) on samples sa- turated with Mg2+ or calcinated at 550°C. By using Weaver’s method (1955) and Jonas and Brown’s graphic method (1959) for threecomponent disordered interstratifications we ob- tain the following main coefficients of probability for the three samples from Figure (b, c and d) : Sample Id : P1( = 0.60 ; PM = 0.35 ; Pc = 0.05 ; Sample Ic : Pir = 0.85 ; PM = 0.10 ; Pc = 0.05 ; Sample 1b : PH = 0.80 ; PM = 0.13 ; Pc = 0.07. (where H = hydromica, M = montmorillonite, C = chlorite). By using Drits and Sakharov’s method (1976) in order to find out the junction factor g, it results that for threecomponent mixed-layer minerals as well, in the conditions PH > 0.75 and PM« = P mhm— 0, the junction factor g is higher that 0, being 1 or 2. Thermodynamic Considerations Both the twocomponent random mixed-layer mineral and the threecomponent one, with a junction factor g = 1 or 2, indicate the presence of some more stable mixed-layer minerals, as the free energy of the system is lower and the pressure and temperature of the for- mation environment are higher. These random mixed-layer minerals have a larger regularity tendency and allow the determination of phy- sico-chemical conditions of thermodynamic transformations in the hydro- metasomatic argiliization stages from the Harghita Mts (Drits, Sa- kharov, 1976). The presence of basal peaks for chlorite (Fig., b) or those for montmorillonite (Fig., d) can be interpreted not only as a discrete pre- sence of these minerals, but also as their segregation tendency. Conclusions In the Harghita Mts zone, the hydrometasomatic argillizations are very widespread and they are represented by the kaolinic stage, the hydromicaceous stage and the mixed-layer stage. The mixed-layer minerals are twocomponent in 9O°/o of cases and threecomponent in 10% of cases ; they are of a random type with a regularity tendency, seldom with a segregation tendency and represent an incipient stage of incomplete transformation of hydromica into .mont- morillonite and chlorite. -• - . -)67 Institutul Geological României 6G V. IANOV1CI et al. 6 REFERENCES Brindley G. W. (1951) X-Ray Identification and Crystal Structures of Clay Mine- rals. Mineralogical Soc., London. Dritș V. A., Sakharov B. A. (1976) X-Ray Structural Analysis of Mixed-Layer Minerals. Ed. Nauka, Moskva. lanovici V., Neacșu G. (1969) Study of the Hydrothermal Argillization Processes from Talagiu. St. cerc, geol., geofiz.. geogr., Geol., 13, 2, 309, București. — Neacșu G., Neacșu Vasilica (1981) Pyrophyllite Occurences and Their Genetic Relatjon with Kaolin Minerals in Romania. Rev. roum. geol., geophys., ge- ogr., Geol., 25, 3, București. Jonas E. C., Brown T. E. (1959) Three-component Interstratification. J. Sediment. Petrol., 29, 77. Mering J. (1940) Lhnterference des rayons X dans les systemes â stratification desordon^e. Acta Crystallogr., 2. Merve C. R., Heystek H. van der (1960) Clay Minerals of South Africa Soil Group III. Soil Sci., 80, 479. — Heystek H. van der (1961) Clay Minerals of South Africa Soil Group. IV. Soil Sci., 81, 399. Neacșu G., Neacșu V. (1980) Fireclay and Kaolin Deposits in Romania. Proc. of the lOth Kaolin Symp. Budapest, Acta Min. Petr., XXIV/1980, Suplemen- tum, 39. — Urcan T. (1975) Hydrothermal Transformati on Phenomena in the Andesite of Pilișca (Harghita Mountains). St. tehn. econ., 1/13, 59, București. — Urcan T. (1978) 10.50 A Hydromica, a Principal Component of “Kaolin” from the Harghita Area. St. tehn. econ., 1/14, 107, București. Setei M., Neacșu G., Urcan T. (in press) New Data Regarding Mineralogical Com- position of Kaolinised Rocks from Vîrghiș Valley and Economical Value of This Area., Proc of the 4th Nat. Clay Conf., București. Weaver Ch. E. (1955) The Distriibution and Identification of Mixed-layer Clays in Sedimentary Rocks. Frec, of the 4th Nat.. Conf. Clays Clay Miner., 385. Petrologie-Mineralogie ERUPTIVE BRECCIAS ASSOCIATED WITH SOME TERTIARY MAGMATITES FROM ROMANIA BY RADU JUDE1, L1DIA JUDE’ The areas with Tertiary volcanics in Romania exhibit eruptive breccia occurrences mainly associated with magmatic bodies in sub- volcanic facies. Their investigation implies several aspects of petrolo- gical and metallogenetic importance. There are several categories of breccias which, according to the classification of Wright and Bowes (1963), belong to the fol- lowing types : (1) intrusion breccia ; (2) explosion breccia ; (3) intrusive breccia. (1) The intrusion breccia is the result of the mechanic effect of magma intrusion in the country rock and occurs frequently in the contact area of subvolcanic magmatic bodies, as well as in some mar- ginal areas of volcanic necks in the Oaș (Tarna Mare), Gutîi (Ilba, Herja, Cavnic, Băiuț, etc) and Metaliferi Mts. (2) The explosion breccia resulted from the explosive action of vapcurs and gases of magmatic nature within a confined space below the surface, is frequently encountered in Neogene volcanics ; it is better developed in mineralization areas in the Metaliferi Mts (Baia de Arieș, Roșia Montană, Deva, etc.). In places it may resemble the collapse breccia, such as the Baia de Arieș breccia bodies (Cochet, 1958). (3) The intrusive breccia is the result of rock fragmentation and mcbilization by magma or magmatic gases, with or without magmatic matrix (Wright, Bowe, 1963) ; it is also widespread in the Oaș Mts (Băile Turțului), the Rodna Massif (Izvorul Roșu, Cobășel Mt), the Me- taliferi Mts (Căraciu volcano, Măgura Țebii, Baia de Arieș, Băița, etc.). The breccia may often have a combined explosive-intrusive genesis and the breccia bodies exhibit a complicated “architecture”. Former geological studies were concerned with the morphology and some aspects of breccia genesis (Cochet, 1953 ; Socolescu et al., 1977 ; Ghițulescu et al., 1979). 1 Faculty of Geology and Geography, Department of Mineralogy, Bul. Băt- cescu 1, București. Institutul Geological României 68 R. JUDE, L. JUDE 2 The present note regards the geological and petrological features of explosion and intrusive breccias from the Metaliferi Mts and the Rodna Massif. One rnay also infer some aspects related to the metal- logenetic significance of eruptive breccia formations. Geological Emplacement and Morphology of Eruptive Breccia Bodies The volcanic explosion and intrusive breccias, generally called eruptive breccias, associate with the Neogene magmatism of subduc- tion areas inși de the Carpathian arc. The breccia bodies, studied by us, associate mainly ■ with quartz andesites and dacites belonging to the second Neogene volcanic cycle, Upper Badenian-Pontian in age (Rădu- lescu et al.,_1981). The best developed and most interesting eruptive breccias belong to the subvolcanic and volcanic complexes from areas with Consolidated, “rigid"’ rocks of Mesozoic or older age, which underwent Neozoic tec- togenesis. The igneous complexes including eruptive breccias occur in elevation areas of the basement (Baia de Arieș) which rnay resemble a horst by shape (Rodna Massif) or within posttectonic depressions over- Fig. 1 — Distribution of Tertiary magmatites with eruptive breccias from Roma- nia. Neogene igneous rocks (1) ; eruptive breccia occurrences (2). 1, Tarna Mare, Turț (Oaș Mts) ; 2, Herja, Cavnic, etc. (Gutîi Mts) ; 3, Izvorul Roșu, Ccbășel (Rodna Mts) ; 4, Baia de Arieș ; 5, Roșia Montană and Bucium ; 6, Almaș-Stănija ; 7, Măgura Țebii, Băița ; 8, Deva (Metaliferi Mts). 3 ERUPTIVE BRECCIAS ASSOCIATED WITH SOMD TERT1ARY MAGMAT1TES 69 Fig. 2 — Geologica] setting of the Izvorul Roșu eruptive Breccia (Rodna Mts). 1, tectonic fractures ; 2, vein containing Pb and Zn mineralizations : 3, sulphide or gold mineralizations of stockwork type ; 4, metasomatie pyrrhotite and/or pyrite mineralizations in limestones ; 5, polymictic eruptive breccias ; 6, amphibole and biotite quartz andesite ; 7, metamorphic rocks : micaschists, amphibolites, crystal- line limestones, etc. Fig. 3 — Geological section through the Afiniș-Baia de Arieș eruptive structure (Metaliferi Mts) (ace. to Ghitu- lescu et al., 1979). 1, gold veins ; 2, gold stockworks — 1, IV, P ; 3, breccia pipes ; 4, subvolcanic microporphyry andesite ; 5, Afiniș andesite subvolcanic bodies ; 6, crystalline limestones ; 7, crystalline schists ; 8, faults. Institutul Geological României 70 R. JUDE, L. JUDE 4 lain by the Neogene molasse (Căraciu-Măgura Țebii, Băița Crăciimești, Stănija, Roșia Montană) (Fig. 1). The breccia bodies are rarely isolated (Deva, Măgura Țebii) ; usually, they form groups within the massive subvolcanic rock or the volcanic necks, next to the contact area or to the boundary with the basement. These relationships are known both in the case of the Baia de Arieș breccias (Ghițulescu et al., 1979) and of the Rodna Veche ones (Jude et al., 1982, 1983). The breccias occur generally as breccia pipes with elliptical, iso- metric or irregular polygonal contour in horizontal section. The Baia de Arieș Breccia pipes exhibit an inclined axis with modulations accompanied dorsally by an explosion breccia including gold minera- lizations (Ghițulescu et al., 1979) (Fig. 3). The rocks surrounding the main pipe may contain dykes or satellite breccia bodies as disclosed by the Izvorul Roșu (Rodna) structure (Fig. 2). The dimensions of breccias vary within wide limits ; the dia- meter of a pipe in horizontal section may be of 30—50 m only (stock- work 3 at Baia de Arieș) or may exceed 200 m in several instances. The breccia pipes are very long and they may exceed 500 m. Some of them crop out, others form blind chimneys. The Izvorul Roșu (Rodna Massif) eruptive breccias exhibit a complex structure owing to a main pipe with irregular polygonal con- tour in horizontal section, accompanied by several breccia dykes and satellite bodies. The breccias and the mineralization were controled by fissure systems generated by vertical stress (Fig. 2). There are instances (Măgura Țebii, Băița Crăciunești) in which the main breccia pipe was emplaced prior to the instrusion of younger quartz andesite dykes (Jude et al., 1973, Cioflica et al., 1968) (Fig. 4). Fig. 4 — a) Geologica! section through the Măgura Țebii subvolcanic structure with eruptive breccias (Metaliferi Mts) (acc. to Jude, 1973, 1989). b) Geologica! section through the Măcieșul-Băița-Crăciunești volcanic structure (Metaliferi Mts) (acc. to Cioflica et al., 1968). 1, Mesozoic eruptive and sedimentary rocks ; 2, Miocene molasse formation ; 3, Neogene andesite pyroclasts ; 4, amphibole andesite (Făerag) ; 5, quartz ande- sites ; 6. eruptive breccias with felsitic matrix ; 7, eruptive breccias with tuffi.site matrix ; 8, tectonic fractures. 5 ERUPTIVE BRECCIAS ASSOCIATED WITH SOME TERTIARY MAGMATITES 71 Petrographic Features of Eruptive Breccias The most common petrographic features are exhibited by the explosion breccia, resulted from the crackling of eruptive rocks under the impulse of magmatic gases without a notable displacement of rock fragments : it is a crackle breccia. These breccias may be deprived of matrix, while the space between the ”fragments“ may be either free or mineralized, generating ore deposits, such as the Baia de Arieș gold stockworks no. 1 and 2, of base metal mineralizafions. The intrusive and expiosive-intrusive polymictic breccias are more frequent and more characteristic. They consist of angular or sub- angular rock fragments of different lithological nature and varied dimensions (frequently from 0.3 to 20 cm, some blocks being bigger than 50 cm), as well as with different matrix. The polymictic breccia consists mainly of andesite, microdiorite or dacite "fragments" (Roșia Montană) accompanied by rock fragments from the breccia pipe walls : quartzites, crystalline schists, crystalline limestones, hornfelses (Rodna, Baia de Arieș), Mesozoic basaltic rocks (Măgura Țebii), Cretaceous sandstones (Roșia Montană) and even “exotic’’ fragments (gneisses) which ascended from the basement. The Izvorul Roșu (Rodna) breccia pipe exhibits remnants of pyrrhotite and pyrite mineralization prior to the breccia ; also magnetite fragments are reported by Udubașa (1974). The breccia fragments are generally unoriented. There are instances in which the fragments exhibit a linear arrangement probably due to the fluidization of the breccia. The matrix of some bodies may be represented by a dense or porous andesite or dacite rock (Măgura Țebii, Metaliferi Mts). More often the matrix is polymictic with ’’tuf- fisite“ aspect ; it consists of millimetric fragments of different rocks (andesites, microdiorites, quartzites. micaschists, limestones, ete.), crystal fragments and volcanic glass (”cinerițe“) generally transformed into postmagmatic neominerals, possibly mineralized. Characteristics of Metasomatic Transformaticns Underwent by Eruptive Breccias and Adjacent Igneous Rocks The pyrometasomatic processes are disclosed by the local occur- rence of a skarn formation including gârneț, diopside, vesuvian and epidote in the contact area of the quartz porphyry microdiorite stock from the Cobășel Mt (Rodna Mts) with the crystalline limestones. The pyrometasornatosis acts partly on the eruptive breccias that occur on the western and northwestern sides of the igneous body, towards its dome, bringing about the concentration of gârneț and epidote within the breccia matrix. A barium-rich neoformation feldspar is added. The high temperature metasomatosis is also characterized by the frequent occurrence of postmagmatic apatite in breccias ; it is a new feature which could be of some petrogenetic significan.ee. Apatite was reported in the breccia matrix, in the Rodna Mașsif, as xenomorphrc crystals and grain agglomerations, associated with tourmaline, rutile and fine casiterite grains in places. In the case of the Măgura Țebii brcc-?'.'*. fine grained apatite is accompanied by clinozoisite, pistacite and quartz ; igr/ Institutul Geological României 12 R. JUDE, L. JUDE 6 at Baia de Arieș, it occurs in highly silicified breecias iand altered andesite rocks. Propylitisation affects the subvolcanic bodies including eruptive breecias almost wholly. The eruptive breecias from the Cobășel Mt (Rodna) and Măgura Țebii (Metaliferi Mts) contain clinozoisite asso- ciated with pistacite and actinote, chlorite and quartz in places which point to high temperature propylitisation. K-metasomatosis is marked on the one hand by the presence of adularia and on the other hand by the concentration of micaceous minerals, mainly of sericite. The adularia either forms pseudomorphoses after the plagioclase of adjacent igneous rocks and of breccia fragments or occurs in idiomorphic crystals associated with quartz within the holes of breecias and on fissures. However, adularia is frequently turned into sericite and/or kaolinic argillaceous minerals. Micaceous minerals of sericite type substitute the feldspar, biotite and in places amphibole of breccia fragments and constituie quartz associated massive concen- trations within the matrix of the Izvorul Roșu Breccia (Rodna Mts). The optical features, correlated with the Chemical analysis data, point to lithium-rich white mica. It is also worth mentioning the concentration of hydrothermal carbonates is certain breccia bodies (Izvorul Roșu, Rodna, stockwork 5 Baia de Arieș, etc.) and the general metasomatosis with argillaceous, kaolinic minerals. Some subvolcanic structures including eruptive breecias are characterized also by the occurrenee of zeolites which disclose the presence of hydrothermal Solutions of alkaline nature. Zeolite meta- somatosis is well developed in the Măgura Țebii andesite subvolcanic complex and in its associated breecias ; it was reported from boreholes at a depth of 500 m. Epistilbite occurs at small depth, while gonnardite occurs at greater depth (Jude et al., 1980). Kelationships Between the Mineralization and the Eruptive Breecias The network of pyrrhotite and pyrite veins in the quartz andesite occurring to the east of the Izvorul Roșu Breccia pipe (Rodna Mts), similar to the metasomatic concentrations in the Rebra Series crystalline limestones (Fig. 2), points to the occurrenee of a mineralization prior to the eruptive breccia. This is also accounted for by the sulphide frag- ments in the breccia. In all the other instances known so far, the mineralization is posterior to the breecias. Thus, sulphide veins or gold mineralizations occur in breecias and adjacent rocks both in the Rodna and the Metaliferi Mts. At Baia de Arieș and Stănija telluride veins occur also in eruptive breecias (lanovici et al., 1969). Another feature is the 'sulphide and/or native gold impregnation of the breccia matrix : the limestone pieces may be partly or wholly substituted by lead and zinc minerals such as in the case of breecias from Baia de Arieș (Lazăr, 1966) or Rodna Mts (Udubașa, 1970 ; Soco- lescu et al., 1977 ; Jude, 1982). The most interesting mineralizations from breecias were reported at Roșia Montană, in the Cetate Mt and at Cîrnic (Cotreanța stockwork). One should also note some explosion 7 ERUPTIVE BRECCIAS ASSOCIATED WITH SOME1 TERTIARY MAGMATITES 73 breccias from Baia de Arieș which include adularia silicified andesite blocks surrounded by centimetric gold quartz crusts (Cochet, 1958 ; lanovici et al., 1969). The mineralization of breccias may also occur as ”gold pyrite“ stcckworks rich in arsenic, as for instance some breccia bodies from the Rodna Mts (Fig. 2) (Jude et al., 1982, 1983). However, the breccia bodies are not homogeneously mineralized ; there are instances in which the mineralization concentrates in the marginal areas and others in which it occurs in the central area of the breccia pipe. On the Genesis of Eruptive Breccias The geological literature of these last 50—60 years offers numerous hypotheses on the genesis of'eruptive breccia pipes. We. note the fol- lowing : explosion due to the vaporization of underground water brought about by ascending magma (Lindgren, Bastin, 1922) ; fluidi- zation of fault breccia and crackled rocks (Farmin, 1941) ; brecciation of rocks at the intersection of fracture zones (Kuhn, 1941, in Mitcham, 1974) ; products of exsolved vapour from magmas (Norton, Chathes, 1973) ; expanding of rocks from the walls of void spaces present in areas with multiple faults (Mitcham, 1974). The eruptive breccia complexes of the type of those occurring in the Rodna Massif (Fig. 2) and the mineralized and non-mineralized fissure systems point out a vertical stress similar to a volcanic explosion. The genesis of the main channel and of fissure systems which include the eruptive breccia may be best accounted for by the model of Norton and Chathes (1973). Gases and magmatic vapours exsolved from magmatic melt accumulated temporarily at the top of a magmatic intrusion situated at small depth in lithosphere rocks. At the criticai pressure, the magmatic vapours were released by explosion along extension fissures from the intrusion dome. Then followed several phe- nomena : decrease of system pressure and temperature, further crystal- lization of magma and rock expanding from the walls of formerly gaseous cavity, the occurrence of eruptive breccia implicitly. Both the size and features of breccia depend on explosion energy ; a low intensity explosion entails the in situ brecciation of rocks (crackle breccia), without notable shift of rock fragments ; on the other hand, a high intensity explosion generates real breccia pipes, accompanied by fissures and eventually breccia dykes. For the most cases, the constitution of eruptive breccia should be looked upon as a complex process achieved during several stages. To the former stage of explosive brecciation succeeded the mobilization of breccia material, possibly accompanied by a new low viscosity magma pulsation due to an increased volatile content. This is disclosed by the oriented texture, with fluidal aspect, of some eruptive breccias with tuffisite of felsitic matrix (Izvorul Roșu — Rodna Massif, Măgura Țebii — Metaliferi Mts). The occurrence of volatile components, fluorine, chlorine (?) and boron is accounted for by the presence of postmagmatic Institutul Geological României 74 R. JUDE, L. JUDE 8 apatite and tourmaline within the matrix of several breccia bodies. Anyhow, the geological literature reporta the occurrence of postmag- matic apatite related to explosive brecciation (Nikitina et al., 1971). The recurrence of brecciation phenomena accounts for the pre- sence of complex structures in which a former breccia generation (felsitic matrix), such as the Măgura Țebii one (Metaliferi Mts), was crossed by a late breccia with tuffisite matrix (Fig. 4). The hydro- thermal solution influx, chemically unbalanced as compared to the breccia material, brought about several metasomatic transformations such as propylitisation, K-alteration with adularia and sericite, argil- litic alteration and other facies previously mentioned. The metallogenetic significance of eruptive breccias is aocounted for by the fact that they are structures which favour the ascending circulation of mineralizing hydrothermal Solutions and they also repre- sent a favourable environment for the deposition of mineral substances. The relationships between the Neogene mineralization and eruptive breccias are very conclusive. The postmagmatic apatite reported from most eruptive breccia bodies may be considered a significant mineral for geological prognosis. According to Williams and Ccsborn (1977) apatite was involved in early stages of hydrothermal systems and concentrated at the top of intrusions including porphyry copper mineralization. REFERENCES Cioflica G., Jude R., Udubașa G., Istrate G., Popescu Gh. (1968) Contribuții la cunoașterea produselor vulcanice neogene din regiunea Băița-Săcărîmb (M. Metaliferi). St. cerc. geol. geofiz. geogr., Geol., 13, 1, 77—92, București. Cochet R. (1957) Contribuții geologice asupra zăcămintelor aurifere de la Baia de Arieș. Rev. minelor, 10, 467—475, București. Ghițulescu T. P., Pitulea G., Ghițulescu I. (1979) Pețrogenesis of the Volcanic Breccia Pipes at Baia de Arieș (Metalliferous Mountains). Rev. roum. geol., geophys. geogr., Geol., 23, 2, 271—281, București. lanovici V., Giușcă D., Ghițulescu T. P., Borcoș M., Lupu M., Bleahu M., Savu H. (1969) Evoluția geologică a M. Metaliferi. Edit. Acad. R.S.R., București. Jude R., Tabacu M., lonescu O. (1973) Studiul geologic și petrografic al rocilor eruptive din zona vulcanului Căraciu (M. Metaliferi). An. Inst. geol., XL, București. Lazăr C. (1966) Contribuții La cunoașterea zăcămîntului polimetalic de la Baia de Arieș (M. Metaliferi). St. cerc. geol.. geofiz., geogr., Geol., 11. 2, 303—315, București. Mitcham Th. W. (1974) Origin of Breccia Pipes. Econ. Geol., 69, 412—413. Nikitina E. I., Sotnikov V. I., Lavrentiev I. G., Semenov V. I. (1971) Evoliuția sostava aksețornovo apatita v endogenom proțesse. Zav. vses. min. obsc., 6, 670. Norton D. L., Challes L. M. (1973) Breccia Pipes — Products of Exsolved Vapour from Magmas. Econ. Geol., 68, 540—546. Institutul Geological României 9 ERUPTIVE BRECCIAS ASSOCIATED WITH SOME! TERTIARY MAGMATITES Perry V. O. (1961) The Significance of Mineralized Breccia Pipes. Min. Eng., 13, 4, 367—376. Rădulescu D., Borcoș M., Peltz S., Istrate G. (1981) Subduction Magmatism in Romanian Carpathians. Guide to Excursion A 2. Carp-Balk. Geol. Assoc. 12th Congr., Bucharest. Sawkins F. J. (1969) Chemical Brecciation, an Unrecognized Mechanism for Breccia Formation. Econ. Geol., 64, 613—619. Socolescu M., Diaconu FI., Varga P. (1977) Structuri de pipe în zăcămintele de sulfuri polimetalice de la Rodna Veche. St. cerc. geol. geofiz. geogr., Geol., 22, București. Udubașa G. (1970) Die structurelle und lithologische Kontrolle Polymetailager- stătte von Rodna (Ostkarpathen). Rev. roum. geol. geophys. geogr., Geol., 4, 1, București. Williams A. S., Cesborn F. P. (1977) Rutile and Apatite Useful Prospecting Guide for Porphyry Copper Deposits. Mineral. Mag., 41. Wright A. E., Bowes D. R. (1963) Classification of Volcanic Breccias. A Discussion. Geol. Soc. Am. Bull., 74, 1. Institutul Geologic al României Institutul Geological României Petrologie-Mineralogie FLUID INCLUSIONS IN HYDROTHERMAL CALCITE AND THEIR SIGNIFICANCE IN CRYSTALLOGENESIS BY VASILE POMÂRLEAN-U \ ELEONORA POMÂRLEANU-NEAGU 2 Introduction The typomorphical features of calcite were studied for the first time by Maucher (1914), then by Kalb (192S) and later by Shkabara (1940 — mentioned by Lazarenko, 1979). Also, the general diagrams regarding the variation of habits of calcite crystals depending on tem- perature conditions are known in literature (Kostov, 1968, 1979 ; Laza- renko, 1979). In this paper, a diagram of crystallogenetic significance for calcite and its minerals associated on the basis of the 770 determinations on the homogenization temperatures of fluid inclusions in 134 calcite samples, from 8 hydrothermal ore deposits, is presented. The diagram gives a correlation between the habits of calcite crystals and homo- genization temperatures of primary fluid inclusions from this mineral. Calcite Crystals The calcite samples have been collected from fissures of volcanic rocks and from hydrothermal veins of the following ore deposits : Herja, Baia Sprie, Cavnic, Băiuț, Țibleș (Gutîi-Țibleș Mountains), Stîn- ceni (Călimani Mountains), Rușchița (Poiana Ruscă Mountains) and Băișoara (Gilău Mountains). The habit of calcite crystals varies from rhombohedron (0221) and scalenohedron (2131), (2131) + (10H), (1010 + (01Î2) to basal rhombo- hedron (1011). Usually each simple or composed form of calcite crystals is asso- ciated with certain minerals (Tab. 1). 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 2 Research Institute of Anorganic Industry and Non-ferrous Metals, Bd. Bi- ruinței 102, Bucharest. JȚ Institutul Geological României igrz 78 V. POMÂRLEANU, E. POMARLEANU-NEAGU TABLE 1 The prevailing crysial forms of calcite, homogenization temperatures of primary fluid iti- clusions and its mineral association Habit Ore deposit Homogenization temperatures (CC) 1 Association no. dct. range maximum frequency (0221) Herja, Băiuț 20 60-80 C (2131) Herja, Cavnic, Țibleș, Ruș- chița 200 80-140 95-100 C- M— J (1010) Herja, Stinceni, Rușchița 250 170-280 190-205 C-A (0112) 255-270 C—S—G;C—F (1011) Cavnic, Stinceni 180 260-375 280-320 C-Py Țibleș 120 250-320 300-315 C—Py—Cp C, calcite; M, marcasite; J, jamesonite; A, antimonite; S, sphalerite; G, galena; Py, pyrite; F, fluorite; Cp, chalcopyrite. Fluid Inclusions Depending on the habit of calcite crystals and the minerals with which calcite is associated, several types of fluid inclusions have been identified (Pomârleanu et al., 1967, 1968, 1972, 1981, 1982). The data on the homogenization temperatures of fluid inclusions in calcite were used to draw up the histograma and frequency curves with which the respective genetic interpretation has been done (Pomâr- leanu, Pomârleanu, 1982). Correlation Between Homogenization Temperatures of Fluid Inclusions and Habits of Calcite Crystals The diagram from Figure represents a correlation between homo- genization temperature of primary fluid inclusions in calcite and ks crystallographic habits. In agreement with the diagram it results that calcite has been crystallized under various temperature condiționa : from below 60—80pC for the habit (0221) up to 370°C for the habit (1011) which is usually associated with pyrite. Fluid inclusions in euhedral scalenohedron calcite associated with marcasite or jamesonite (Herja and Cavnic) show homogenization tem- peratures of 80—140°C (Tab., Fig. ). Inclusions in the same form of calcite crystals from districts : Korsnăs-Finland (Rehtijărvi, Kinnunen, 1979), Laisvall-Sweden (Roedder, 1968) and Central Siberian Platform (Andrusenko, 1971) have homogenization temperatures in the same range. Institutul Geologic al României 3 FLUID INCLUSIONS IN HYDROTHERMAL CALCITE 79 Fig. _ Diagram showing the correlation between the habits of calcite crystals and homogenization temperatures of primary fluid inclusions from this mineral. Conclusions In this paper is presented a diagram that shows a correlation between homogenization temperatures of fluid inclusions in calcite and its crystallographic habits. The homogenization temperatures vary from Institutul Geological României 80 V. POMARLEAJTO, E. POMARLEANU-NEAGU 60—80°C for the habit (0221) up to 375°C for the habit (1011) which is usually associated with pyrite. The diagram may be used in elucidating the crystallogenetica'l conditions both of calcite and its mineral associations. REFERENCES Andrușenko N. I. (1971) Minerăloghia i ghenezis islandaskovo spata Sibirskoi .platformî. Izd. ,,Nedra“, Moskva. Kalb G. (1928) Die Kristalltracht des Kalkspates in mineralogenetischer Bertracht- ung. Cbl. Min. Abt. R, 337—338. Kostov L. (1971) Mineralogy. „Mir“ Press. Moskva. Kostov I. (1978) Morphology and Genesis of Minerals. Reghionalnaia i ghene- ticeskaia mineraloghia, 2, „Naukova Dumka“, 3—15, Kiev. Lazarenko E. K. 1979) Opît gheneticeskoi klassifikații mineralov. „Naukova Dumka“, 312, Kiev. , Maucher W. (1914) Die Bildungsreihe der Minerahen als Unterlage fur die Einteilung der Erzlagerstătten. Freiberg, 56. Pomârleanu V., Petreuș I. (1967) Noi date asupra geotermometriei zăcămîntului hidrotermal de la Herja (Baia Mare). Rev. minelor, 7, 320—324, București. — Petreuș I. (1968) La geothermometrie de la calcite et de la fluorine basee sur l’etude des inclusions fluides du gisement hydrothermal de Cavnac (Baia Mare), Anal. șt. Univ. „Al. I. Cuza“, Secț. II, Șt. nat., Geol.-Geogr., XIV, 1—5, Iași. — Movileanu A.. Murariu T., Mihâlka St. (1972) Contribuții la studiul minera- lizației polimetalice de la Rușchița. D. S. Inst. geol., LIX/2, 81—104, București. — Peltz S., Balla Z. (1981) Studiul incluziunilor fluide în aria mineralizației hidrotermale asociate structurii eruptive Zebrac-Mermezeu (Stînceni, Munții Călimani). St. cerc, geol., geofiz. geogr., Geol., 26/2, 233—240, București. — Pomârleanu Eleonora (1982) Fluid Inclusions in Calcite of Some ore Deposits in Romania. Current Research on Fluid Inclusions. Chem. Geol., V, 37, .162—172, Amsterdam. Rehtijărvi P., Kinnuenen K. (1979) Fluid and Mineral Inclusions and Inclusion Zones of Cave Calcite from Korsnăs Mine, Western Finland. Bull. Geol. Soc. Finland, 51, 75—79. Roedder E. (1968) Environment of Deposition of the Disseminated Lead Ores at Laisvall, Sweden, as Indicated by Fluid Inclusions. Intern. Geol. Congr. 23rd, 7, 389—401, Prague. Institutul Geological României Petrologie-Mi neralogie A BIMODAL IGNEOUS COMPLEX OF NEOGENE AGE, ȚIBLEȘ, EAST CARPATHIANS, ROMANIA by N1COLAE POP1, GHEORGHE UDUBAȘA3, OSCAR EDELSTEIN3, VERA POP1, MARINEL KOVACS3. GHEORGHE DAMIANDUMITRU 1STVAN3 DRAGOȘ STAN3, ALEXE BERNAD3 Introduction The Țibleș igneous complex is located between the Oaș-Gutîi and Călimani-Harghita segments of the Neogene vulcanic Chain in the East Carpathians. It builds up together with Toroiaga, Rodna and Bîrgău units the so-called subvolcanic zone (Peltz et al., 1972). This paper summarizes the main structural and petrologie features of the Țibleș igneous complex, which exhibits a bimodal character as compared to the other igneous units of Neogene age in Romania. Geologic Setting and Structure of the Igneous Complex The Țibleș igneous complex is situated southwards of the Bogdan Vodă (E-W) transcrustal fault, where the Oligocene-Miocene sedimentary rocks of the Autochthon underlie the Paleogene ones of the Wiidflysch Nappe and of the central tectonic unit (Fig. 1). The igneous bodies cut sedimentary rocks of Paleogene and Lower Miocene age with contact metamorphic overprints ; the age of magma- tites is thus undoubtedly post-Lower Miocene (Edelstein et al., 1981). The Earth’s crust is here 30-35 km thick (Socolescu et al., 1975) and the nappe group of the Oriental Dacides constitutes the basement. The igneous complex consiste of three units : (a) the SE unit (Arcer-Țibleș- Măgura Neagră), (b) the central unit (Tomnatec-Stegioara-Hudieș) and (c) the NW unit (Hudin). The SE unit includes the main igneous body consisting of a central stock of composite constitution and an externai ring-like zone ; in the vicinity there are many smaller igneous bodies 1 Institute of Research. Technological Engineering and Designing for Non- ferrous Ores, str dr. V. Babeș 62, 4800 Baia Mare. 3 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 3 Enterprise for Geological Prospection and Exploration "Maramureș”, str. Victoriei 146, 4800 Baia Mare. 6 - c. 657 N. POP et al. 2 82 Institutul Geological României 3 BIMODAL IGNEOUS COMPLEX OF NEOGENE AGE— TiBLEȘ 83 as suggested by geophysical dala. Institutul Geological României 81 N. POP et al. 4 of varying composition (Fig. 1, Tab. 1). At .a depth of about 1000 m the geophysical data suggest a unitary and nearly circular form of the entire SE igneous unit. The central unit includes microgranodiorites in the north and many bodies of intermediate composition in the south and in the central part. Some of them are composite as a result of polystadial igneous activity (Pop et al., unpublished). The NW unit contains the Hudm intrusive cupola with dominant microgranodiorites and small dacite bodies around it (Fig. 1). Petrography The Țibleș igneous rocks constituie two main igneous formations : a) acidic and b) intermediate formation. The first one is compositionally homogeneous with small structure and texture variations ; it consists of microgranodiorites and dacites. The intermediate Fm is compo- sitionally more complex and shows marked transitional features, as well as a heteromorphic character (according to Rittmann, 1973). It consists of two distinct rock suites : (1) monzodiorites-monzogranites and (2) tonalites (Tab. 1). The petrotypes have been established by using the classifications of both Streckeisen (1967) and Rittmann (1973). The main minerals are plagioclases (plg), elino- and orthopyroxenes (cpx, opx), amphibo- lites, + biotite, quartz, alkali feldspars. The opaque accessories are • magnetite, ilmenite. rutile, chalcopyrite, pyrrhotite and pyrite ; the other include apatite, sphene, zircon, orthite. Corroded quartz pheno- crysts and cordierite were observed only in the rocks of the acidic Fm. The typical mineral assemblages are : (1) plg (An60_80)-cpz (mag- nesian augite)-opx (40% FeSiOJ+amphibole, in gabbrodiorites, two pyroxene diorites, latite andesites ; (2) plp(An3-_85)-cpx-opr (70% FeSiO3) amphiboleibiotite-quartz, in quartz diorites, tonalites, plagidacites ; (3) plg (An40_w)-cpx (calcic augite)-opx (hypersthene)-amphibole-alkali feldspar (orthoclase, anorthoclase)-quartz, in monzodiorites ; (4) plg (An45_C5 )-pr-amphibole-biotite-quartz (euhedral phenocrysts)-cordierite- alkali feldspars (anorthoclase, sanidine), in the rocks of the acidic Fm. For more details see Pop et al. (in press). Petrochemistry There were about 130 available Chemical analyses ; most of them (112) are made on the rocks of the intermediate Fm (the acidic Fm contains more altered rocks). The Chemical components obey as a rule the normal distribution law. SiO2, TiO2 and, to a lesser extent, A12O:> show bimodal distributions (Fig. 2a), the two modes corresponding to the acidic and intermediate formations. The last one exhibits a normal distribution of these components too (Fig. 2b). The average chemical composition (Tab. 2) matches well (excepting the acidic Fm) the che- mistry of the andesitic rocks (Taylor, 1969 ; Gill, 1981). The CIPW and Rittmann norms suggest the transitional and heteromorphic cha- racter of the petrotypes reflecting fhus the actual conditions, i.e. plutonic and (shallow) subvolcanic, under which the rocks Consolidated. Nor- HHt- Institutul Geologic al României IGR/ BIMODAL IGNEOUS COMPCEX OF NEOGENE AGE-TIBLEȘ mative corundum and cordierite appear by calculating CIPW and Ritt- mann norms, respectively. On the QAP diagram (Fig. 3) the rocks of the acidic Fm occupy mainly the granodiorite field, whereas the rocks of the intermediate Fm clearly follow two distinct trends : (A) of monzodiorites-monzogranites. and (B) of tonalites-granodiorites. Ac- Fig. 2. — SiO> and TiO> distribution ot Țibleș magmatites. a, global ; 2, intermediate formation. Fig. 3. — QAP diagram. 1, monzodioritic suite ; 2, two pyroxene latite andesites ; 3, two pyroxene quartz diorites (± am- phiboles)-tonali te ; 4, tonalites ; 5, plagidacites-two pyroxene and am- phibole dacites ; 6, acidic forma- tion ; A, monzodiorite-monzogranite trend; B, tonalite-granodiorite trend. 80 N. pop et al. 6 cording to the K2O-SiO2 diagrams of Taylor (1969) and Peccerillo and Taylor (1976) the rocks of the intermediate Fm belong mainly to ande- sites and K-rich andesites (Fig. 4). On this diagram the main evolution trends can alsc be seen : (1) of K-enrichment (K-rich andesites and dacites), and (2) of maintaining, or even decreasing, the K content TABLE 2 Mean Chemical composilions of Țibleș magmalitcș Oxidcs a b 2 $ b 3 c d c 4 5 6 7 8 Si O» 53.29 54,95 55,12 56,93 57.89 59.40 59.83 63,53 57,75 59,16 63.65 69,66 57,16 ai.o3 17,94 .17,53 ,20,00 16,35 16.68 16.00 16,47 14,48 18,'14 16.92 17,55 16,45 17,16 Fe2O» 3.84 4,13 2,07 3,44 1,72 1,72 3,42 1,37 3,25 3,47 1,67 ,531 3,19 FeO 4*74 5,25 3,49 4,74 4,77 4,38 3,55 3,24 4 ,â2 3,69 2,71 1 .36 4,39 l.fnO 0.18 0,23 0,10 0,18 0,13 0.13 0.13 0,10 0.16 0.17 0,13 0,09 01,7 MgO 4,53 3,71 2,99 3,69 3.21 3.09 3.02 2,29 2.73 2,76 1 .92 0,83 3.41 CaO 8.94 7,74 8,47 7,02 6,18 6. 11 5,82 2.36 6.70 5,88 4,71 2,30 7,04 Na2O 2,67 2,69 2,60 2,80 2,84 2,71 3.00 2.25 2.6 3,33 3,10 2,79 k2o 1,13 1,24 1,82 2.10 3,67 2.86 2,46 3.35 1 .48 1 .33 1,58 2,41 1 .88 TiO, 0,73 0,69 0,63 0.78 0,91 0,72 0,49 0.60 0.79 0.89 0,45 0,18 0,71 p2o5 0,15 0,16 0,17 0,17 0,19 0,19 0,16 0,15 0,15 0,13 0,13 0,11 0,16 An-n 53,1 51,7 52,5 40,9 32.3 36,0 38 28 49,2 16.8 46,3 17,8 DI 37,7 41,8 43,0 49,9 54,2 53,7 55,3 62,8 47,5 51 ,6 58,6 77.0 N-A 1,2 1 .9 2,1 3,4 5.2 5,7 7.0 5,0 3,7 3,6 6,7 0,47 10,7 K2O 0,42 0,46 0,7 0,75 1,29 1,04 0,89 1,12 0,59 0,50 0,78 Na2O L gabbrodiorites: a) coarse grained (d 2 mm) (n=8); fine grained (n=4); 2, pyroxene latite-andesites (n = 16); 3: a, quartz monzodiorites (n = 30); b, quartz monzodiorites-quartz monzonites (n=l); c, quartz. monzodiorites-granodiorites (n = 4); d, microgranodiorites in satellite bodies (n = 7); e, monzogranites (n=4); 4, quartz diorites-tonalitcs-granodioritcs (n = 26); 5, plăgi dacites-amphibole and two pyroxene dacites (n = 9); 6, tonalites-granodio- riles (n = 4);7, microgranodiorites-microgranites-dacites-rhyolitcs (n = 18) (acidic formation); 8, mean Chemical composition of the intermediate formation (coluinns 1 — 6) balanced with the outeropping arca. An-n — normative anorthite. (normal andesites and dacites). The FeO*/MgO-SiO2 diagram (Fig. 5) suggests the congruency with the orogenic calc-alkaline andesites (ac- cording to Gill, 1981) as well as some affinities (for certain rocks) to the tholeiitic andesites. However, the dominant calc-alkaline trend is seen on the Na2O-|-K2O/SiO2 diagram (Fig. 6),- which stresses, in ad- dition, the superealcic and calcic character of the rocks. The “con- tinental” evolution trend of the Țibleș magmatites may partly be depicted on the Al2O3/CaO-|-Na2O-|-K2O-SiO2[N-A] diagram (Fig. 7) A normal feature has the Nockolds-AUen index related minor element distribution ; Ba and Zr increase as the index increases, 7 BIMODAL ÎGNEOUS COMPLEX. OF NEOGWE AGE—ȚIBLEȘ 87 whereas Cr, Ni, Co, Sc and V decrease ; Y, Yb and Ga rentam un- changed. The distribution diagrams of the minor eiements in the Țibleș rocks are astonishingly similar to the diagrams of Taylor (1969) for andesites (Udubașa et al., in press). Fig. 4. — K-O-SiOj diagram of intermediate formation. 1, gabbrodiorll.es: ooarse grained ; 2, gabbrodicrites : line grained : 3, two pyroxene latite andesites ; 4, monzodiorites (± quartz) ; 5. quartz monzodiorites-quartz monzomtes ; 6, quartz monzodiorites- granodiorites ; 8, monzegranites ; 9, quartz diorites-tonalites-granodiori- tes ; 10, plagidacites-two pyroxene and amphibole dacites ; 11, tonalites; 12, mean values of petrotypes. I, island arc tholeiitic serios ; II, calc-alkaline series ; !L, high-K calc- alkaline series : IV, shoshonite series ; 1*. low-K basaltic andesites ■ 2*, basaltic andesites ; 3*, andesites ; 4*, high-K andesites ; 5*. high-K basaltic andesites (ace. to Peccerillo and Taylor, 1976). A. B, C, D. evolution trends (see the text). Institutul Geological României 88 N. POP et al. 8 teO"/ MgO Fig. 5. — Mean petro- types plotted on FeO*/ MgO-SiOj diagram (for symbols see Fig. 4). TH, tholeiitic andesites; CA, calc-alkaline ande- sites; HRS, hypersthene series ; PRS. pigeonite series; I, non-oroge- nic andesites (Tingrnuli, Iceland) (acc. to Gill, 1&81). Fig. 6. — Alkali-SiO2 diagram (for symbols see Fig. 3). Fig. 7. — Țibleș mean petrotypes plotted on SiO2-Al-.O3/CaO+Na2O + -t-K2O diagram. Lines of “arc” and “continental” trends acc. to Feiss (1980). A, tonalite trend; B, monzodiorite- monzogranite trend. Institutul Geological României 9 BIMODAL IGNEOUS COMPLEX OF NEOGEINE AGE—ȚIBLEȘ 89 Discussion The Țibleș igneous Complex has appeared as a result of two-phase -magmatic activity evolved under non-volcanic conditions. The igneous rocks show a clearly bimodal character. The first main phase had a unique magmatic event and gave rise to the acidic Fm Consolidated at shallow depth (subvolcanic). The second main phase appears to be Chemical discontinuii/ ---SiO^/o— Fig. 8. — Magmatic evolution trends of the intermediate formatin according to the differentiation index (D.I.) and SiO> (for symbols see Fig. 4). A.F. X formed during more than two magmatic events giving rise to the intermediate Fm formed at greater depths (subvolcanic-piutonic). The evolution of the latter phase exhibits two distinct trends : (1) of K en- richment (monzodiorites-monzogranites) and (2) of K depletion with SiO2' increase (tonalites-granodiorites). These two trends are clearly deveioped on the DI-Si62 diagram (Fig. 8). on which a gabbrodiorite trend exists too. The two igneous formations derived from dominant andesitic magmas which have been issued by lithosphere subduetion at the west- ern margin of the Eurasian Plate. The firstly formed acidic Fm evolved from a magma supply with simpler evolution and shows more signs of contamination with sialic matter (suggested by the presence of cordierite and corroded quartz phenocrysts). This first magmatic phase lacks in metallogenetic products. Afterwards, probably from a different depth, a new amount of little differentiated magma (compositionally similar to the quartz monzo- diorites — see columns 8 and 3A in Table 2 — and to the orogenic andesites) was located in two main magmatic chambers with inde- pendent evolution. The first one — situated in the NE unit — has generated, by nearly in situ differentiation, the monzodiorite suite with three igneous events resulting in the formation (1) of the ring rocks, (2) of the central stock, and (3) of the vein rocks. The second magmatic chamber — situated in the central tectonic unit — had a vertical zoning and gave rise to the tonalite suite with two igneous events : (1) formation of plagidacites and two pyroxene amphibole tona- 90 N. POP el al. 10- lites, from the magma position in the apical part, and (2) formation of two pyroxene diorites from the deeper part. Mainly base metal ore veins are developed in connection with the intermediate Fm ; in ad- dition, some disseminated ores (Cu, Mo, etc.) are also known (for details see Udubașa et al., in press). Island arc setting on continental lithosphere rnay explain some mixed characters of this rock association, i.e. of orogenic calc-alkaline andesites with well marked tholeiitic tendencies. AII the structural and petrographic-petrochemical peculiarities of the Țibleș igneous Complex including some locally developed specific alteration zones are similar to the porphyry (copper or molybdenum) systems as discussed by Udubașa et al. (in press). REFERENCES Edelstein O., Istvan D., Bop N.. Răduț M., Kovacs M., Stan D.. Bernad A., An- drei J., Pop V., Gotz A., Bordea R., Roman L. (1981) Alcătuirea geologică a munților Țibleș. Communication Inst. geol. geofiz., București. Feiss G. P. (1980) Major element Controls’ on copper availability in porphyry copper systems. In : S. Jankovic, R. H. Sillitoe (Eds.) European Copper Deposits, 36-41, Belgrad. Gill J. B. (1981) Orogenic andesites and plate tectonics. Springer, Berlin-Heidel- berg-New York. Peccerillo A., Taylor S. R. i'1976)' Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastaru .au area, northern Turkey. Contr. Miner. Pet-r., 58, Heidelberg. Peltz S., Vasiliu C., Udrescu C. (1972) Petrologia magmatitelor zonei subvulcanice neogene din Carpații Orientali. An. Inst. geol., XXXIX. 177-256, București. Rittmann A. (1973) Stable mineral assemblages of igneous rocks. Springer, Berlin- Heidelbeng-New York. Socole-scu M., Ciocîrdel R., Airinei St., Popescu M. (1975) Fizica și structura scoar- ței terestre din România. Ed. tehnică. București. Streckeisen A. L. (1967) Classification and nomenclatura of igneous rocks. N. Jb. Miner. Abh., 107, 144-240, Stuttgart. Taylor S. R. (1969) Trace element chemistry of andesites and associated calc- alkaline rocks. In : Proc. Andesite Conference. Dept. Geol. Min. Res. Oregon Bull., 65, 45-63, Portland. Udubașa G., Edelstein O., Pop N., Răduț M., Istvan D., Kovacs M., Pop V., Stan D., Bernad A., Bratosin I., Gotz A. (1984) The Țibleș Neogene Igneous Complex of North Romania : Some Petrologie and Metallogenetic Aspects. An. Insl. Geol. Geofiz., LXII (Trav. Xlie Congr. Assoc. Geol. Carp.-Balk.). București. Petrologie—Mineralogie LE METAMORPHISME DES CHARBONS DES CARPATHES MERIDIONALES ROUMAINES PAR GHEORGHE C. POPESCU1, ION PREDA1, COSTEL NEDELCU2 Le dernier temps, pour la caracterisation des charbons, on a uti- lise, de plus en plus, des methodes optiques quantitatives et la diffrac- tion Rx (Landis, 1971 ; Grew. 1974 ; Kisch, 1974 ; Diesel. Offler, 1975 ; Kwiecinska, Kajizar, 1975 ; Kwiecinska, 1980). Cela a permis une cov- relation assez exacte des stades ele transformation du graphite et des etats pregraphitiques au degre de metamorphisme des roches hote de- duit des parageneses des mineraux silicates (Kwiecinska, 1980). En Roumănie de telles recherches ont ete entreprises sur I’anthracite de la formation de Schela (Popescu, 1982) et sur les houilles anthraciteuses de Banat (Preda, Nedelcu, 1983). Les depots charbonneux des Carpathes Meridionales se trouvent dans des conditions structurales differentes et ont des âges differents, fait qui donne la possibilite de comparer le degre de carbonification avec le metamorphisme des roches hote, pour arriver â des conside- rations concernant les causes du degre differencie de metamorphisme des depots synchrones. Les resultats des recherches qu’on va presenter se basent speciale- ment sur les investigations de la refletivite de la vitrinite des echan- tillons de charbon d’âge Carbonifere de Baia Nouă-Cucuiova et Lupac et de charbon d’âge liasique d’Anina, Pregheda et de la formation de Schela. De plus, nos recherches ont ete effectuees aussi sur certains echantillons de graphite de Baia de Fier. Parallelement aux investiga- ticns optiques quantitatives, on a analyse le meme materiei par la diffractidn Rx. Considerations geologiques Dans les Carpathes Meridionales se trouvent des charbons hu- miques differents en tant qu’âge et degre de carbonification tant sur 1 Universite de Bucarest, Faculte de Geologie et Geographie, Bd. N. Băl- cescu 1, Bucarest. 2 Entreprise de Prospections Geologiques et Geophysiqu.es, str. Caransebeș 1, 78344 Bucarest. 92 GH. POPESCU et al. 2 Fig. 1 — Repartition des formations a charbons sur l'esquisse des Carpathes Meridionales. Sarmatien-Tortonien : 2, Miocene-Oligocene ; 3. Cretace superieur ; 4, Lias : 5, Carbonifere ; 6, cristallin ; 7, ligne de chevauchement (domaine getique), 3 LE METAMORPHISME DES CHARBONS DES CARPATHES MERIDIONALES 93 le domaine de sedimentation getique que sur l’autochtone danubien. De meme, on trouve des charbons dans les bassins post-tectoniques intermontagneux (fig. 1). Les formations cristallines de l’autochtone danubien contiennent â Baia de Fier, d’importantes quantites de graphite. Les premisses de la formation des charbons dans les Carpathes Meridionales ont existe deja depuis le Precambrien (le graphite du cristallin de Lainici-Păiuș — PaPtochtone danubien), mais les gisements d’importance economique se sont formes â partir du Carbonifere, comme suit : — sur le domaine getique : Lupac et Secul — houilles anthraci- teuses (Carbonifere) ; Anina et Doman — houilles (Lias) ; — sur l’autochtone danubien : Baia Nouă-Cucuiova — houilles anthraciteuses (Carbonifere) ; Cozla-Camenița — houilles ; Pietrele Albe, Biger, Pregheda, Svinecea Mare — houilles anthraciteuses ; Schela, Valea Izvorului, Jieț — anthracite (Lias) ; — dans les bassins post-tectoniques : Rusca Montană — charbon brun, houilles (Cretace superieur) ; Petroșani — houilles, charbon brun (Oligocene-Miocene) ; Caransebeș-Mehadia. Bozovici — lignite, charbon brun (Miocene). Les recherches effectuees par Răileanu (1953. 1963), Năstăseanu (1964, 1973, 1978 etc.) ont conduit ă la connaissan.ee de la succession geologique des depots de charbon. Mateescu (1956-1968) a presente des donnees concernant le metamorphisme des charbons. Enfin, Manolescu (1933), Bițoianu (1973) et Semaka (1962) ont mis en evidence la flore genera trice de charbons. Pendant le Carbonifere les charbons se sont formes dans des bas- sins lacustres de basse altitude (bassins limniques) instales apres la phase d’orogOnese sudete pendant le Westphalien-Stephanien par l’ac- cumulation de la vegetation de marais (gisements autochtones). L’orogenese asturienne a ete accompagnee par des eruptions (roches eruptives. agglomerats volcaniques, tufs etc.) intercalees dans les com- plexes charbonneux de Baia Nouă-Cucuiova, qui ont diminue les condi- tions favorables au developpement et ă l’accumulation de la vegetation. La sedimentation lacustre reprise pendant le Permien inferieur a cesse dans la phase d’orogenese saalique accompagnee par de considerables phenomenes volcaniques. Les phases tardives de l’orogenese hercynienne ont soumis ă l’ero- sion les depots paleozoîques et la ba.se cristalline durant tout le Trias. Ce n’est qu’au debut du Jurassique que la mer s’est installee dans les Carpathes Meridionales en occupant au debut les zones de depressions tectoniques dont les marges plus mobiles ont ete couvertes temporaire- ment par des marais favorables â la formation des charbons. Ces zones paraliques et aux charbons autochtones se sont superposees sur les zones mobiles du Carbonifere. Le nombre reduit des couches minces de charbons intercalees dans les depots, generalement grossiers, prouve une subsidence rapide et saccadee â courtes periodes de calme durant lesquelles se sont formes les sehistes argileux â charbons. A partir du Lias moyen le milieu marin s’elargit et la sedimenta- tion continue jusqu’au Cretace superieur y compris. Les tectogeneses 'A Institutul Geological României igr/ 94 GH. POPESCU et al. 4 alpines (les phases autrichienne, soushercynienne, laramienne) ont plisse et replisse les depots mesozoiques et paleozoîques tout en formant les synclinoriums de Reșița-Moldova Nouă et de Sirinia-Svinecea, orientes NE-SO, affectes par plusieurs fractures longitudinales et transversales accompagnees souvent par d’importants decrochements. Ont ete mis en place les nappes getique et de Sever in, des corps des roches magma- tiques connus sous la denomination de banatites qui donnent des phe- nomenes interessants de contact a Rusca Montană. A Petroșani, bassin pâralique â charbons autochtones, les depots sont fortement tectonises dans la pârtie d’ouest et les charbons pre- sentent un degre avance de carbonification. Les bassins post-tectoniques miocenes contiennent des lignites pas- sables aux charbons bruns. Les depots sont faiblement plisses et ils presentent des fractures ă d’importants elenivellements. Composants petrographiques Les composants petrographiques identifies par les analyses effec- tuees sur Ifes sections polies par Mateescu (1956-1972), Bițoianu (1972), Popescu et al. (1982), Preda et Nedelcu (1983) sont presentes dans le tableau 1. TABLEAU 1 Les composants petrographiques des charbons de principaux gisements des Carpathes Meridionales Gisement Âge Degră de carbonification Microlithotypes, % Subst. min6- rales, % Mat. vola- ' tiles, % Vitritc Clari te Dorite Fusite Petroșani Miocene- Oligocene Houilles 45-88 5-30 1-7 2 5-7 27 Roman Lias Houilles 83-86 abs. abs. 9-20 3-16 11-27 Anina Li as Houilles 18-72 2-3 7 — 75 2-50 5 28-36 Preghcda Lias Houilles anthra- citeuses 61-86 abs. abs. 6-31 6-14 2-4 Schela Lias Anthracite 75-93 abs. abs. 8-25 5-10 2-6 Secul Carbonifere Houilles G2-8G 0-10 abs. 1-8 8-27 18 Lupac Carbonifere Houilles anthraci- teuses 90 abs. abs. 5 / 5 3-4 Baia Nouă Cucuiova Carbonifere Houilles anthraci- tcuses 60-70 5-7 10-20 1-2 3-5 9-10 Baia dc Fier Precambrien Graphite — — — — — — .5 LE METAMORPHISME DES CHARBONS DES .CARPATHES MERIDIONALES 95 Donnees optiques quantitatives Les determinations de refletivite (R) pour la vitrinite ont ete rea- lisees au microscope Amplivale Palphotometrie Karl Zeiss Jena pour ies longueurs d’onde de 487 m, 552 m, 591 m, 658 m. en air â l’etalon de silice. A base de ces resultats on a elabore les courbes de dispersion pour chaque type de charbon (fig. 2). II en resulte que : — Ies valeurs de R et de la bireflexion (AR) augmentent ă mesure qu’on passe de l’houille â l’houille anthraciteuse-anthracite. ces valeurs etant plus grandes pour l’anthracite de Schela-Gorj ; — on ne constate point de relation entre l’âge des charbons et le R, fait bien illustre si on compare les houilles de Petroșani (Oligo- eene-Miocene) â celles d’Anina (Lias) ; — dans le cas des charbons du Carbonifere, les courbes sont sen- siblement semblables. Mais ceux du Lias different beaucoup en fonction du gisement. Cela est visible tant dans le cas des charbons liasiques de Banat autant que dans celui de l’anthracite de la formation de Schela. Les investigations Rx se sont realisees sur des echantillons pre- leves des gisements de charbons appartenant au Carbonifere, Lias et Oligo-Miocene a l’aide du diffractometre Phillips ă l’anticathode do Cu. filtre de Ni â 35 Kv, 15 mA, vitesse du goniometre de l°/min, vitesse de deplacement du papier de 600 m/h, etalon interne KC1. II en resulte que : — les diffractogrammes des charbons carboniferes n’indiquent au- cun reflet pour les plâns basaux (002) et (004). Un comportement simi- laire ont aussi les.houilles liasiques d’Anina et celles oligocene-mio- cenes de Petroșani. En echange l’houille anthraciteuse de Pregheda, tou- jours du Lias, est le seul type de charbon qui presente un reflet diffus pour le plan basal (002) ; — Ies diffractogrammes de l’anthracite de la formation de Schela revelent pour tous les echantillons analyses un caractere diffus des reflexions des plâns basaux (002) et (004) en comparaison avec les diffractogrammes du graphite de Baia de Fier. Pour le reflet (002) on a decouvert deux ou trois valeurs qui sont plus grandes que doo2 du graphite (3.36 A) et varient entre 3,43-3.59 A. Ces valeurs se superposent sur l’intervalle 3.40-3.75 A, caracteristique aux phases de passage de charbons a graphite (Landis, 1971 ; Kisch, 1974 ; Kwiecinska, 1978). Commentaire sur les resultats La correlation des donnees concernant la refletivite de la vitri- nite avec celles resultces de l’examination des diffractogrammes râ- vele que : — les charbons carboniferes — houilles ahthraciteuses — prs- sentent une faible tendance de rangement de la vitrinite. fait soutenu par la baisse valeur du R ( <9%) et de son anisotropie tres reduite (A R < 1). Cette caracteristique releve le fait que les diffractogrammes fc- '>86 551 589 636 686 551 589 636 Xnm Fig. 2 — Les courbes de dispersion des mesurages R pour la vitrinite. : 1, graphite (Baia de Fier) ; 2, houille anthraciteuse (Lupac) ; 3, houille anthraciteuse (Baia Nouă-Cucuiova ; houille (Petroșani) : B : 1, anthracite (Schela) ; 2, anthracite (Valea Izvorului) ; 3, anthracite (Jieț) ; 4. houille anthraci- teuse (Pregheda) ; 5, houille (Anina), 7 LE METAMORPHISME DES CHARBONS DES CARPATHES MERIDIONALES 97 de ces charbons demontrent quelque fois seulement des inflexions tres larges et de petite intensite pour les plâns basaux (002) et (004) ; — les charbons du Lias — houilles et anthracite — presentent des caracteristiques differentes tant au point de vue du R et A R que de la diffraction Rx. Ainsi l’houille d’Anina presente les plus basses valeurs du R vis-â-vis de tous les charbons analyses. Par la diffrac- tion Rx, on n’a pas remarque, dans son cas, l’individualisation d’une certaine inflexion dans les plâns basaux (002) et (004). En echange, Fig. 3 — Metagres â l'anthracitoclaste aux „ombres de pression“ de quartz fibreux. Formation de Schela — Vailee de Jieț, lame mince, N +, X 60. rhouille anthraciteuse de Pregheda releve des valeurs sensiblement plus elevees par rapport â rhouille d’Anina et l’anisotropie est elle aussi un peu plus elevee. En corroborant ces caracteristiques avec l’inflexion diffuse, mais bien individualisee, du plan basal (002), on constate l’individualisation incipiente de certaines structures pregraphitiques. Ces observations sont en correlation aussi avec celles optiques qualitatives qui ont revele â Pregheda le caractere anisotrope de la vitrinite. Le caractere plus avance de carbonification de la vitrinite de ce gisement a ete deter- mine par l’action des Solutions epigenetiques qui ont cristallise la pyrite et le quartz (fig. 3). II en resulte donc que les charbons liasiques et carboniferes de Banat ont un degre de carbonification intermediaire 7 - c. 667 Institutul Geologic al României \IGR/ 98 GH. POPESCU et al. 8 entre les phases â contenu reduit en carbone (lignite, charbon brun) et les phases â contenu riche en carbone (anthracite, metaanthracite). Par rapport aux caracteristiques petrographiques des roches hote, on constate une correlation avec leur caractere intensement diagenetique, argumente par la presence de l’illite, de la muscovite et du quartz secondaire de surcroissance sur des granoclastes initiaux (Fig. 4). Fig. 4 — Schiste ă pyrophyllite et chloritoîde prismatique radiaire. For- mation de Schela — Gorj, lame mince, N -r, X 60. L’anthracite de la formation de Schela (Schela-Gorj, Izvorul-Jiu, Jieț), la troisieme categorie de charbons analyses, se place par ses caracteres roentgenostructuraux et optiques quantitatives (R) dans la categorie des phytoclastes (phase de transition) caracteristiques a l’an- chimetamorphisme (Popescu et al., 1982). Qualitativement, la vitrinite qui represente le microlithotype majoritaire est visiblement anisotrope et â Schela-Gorj on observe meme des bandes ă caractere graphitique, fait justific par les valeurs relativement elevees du R (14-18%) et du △ R (fig. 2). Dans ce cas, les roches hote, les schistes ă pyrophyllite et â chloritoîde, les metagres et les schistes â paragonite-muscovite, ont des caracteristiques mineralogiques qui, au point de vue du degre de metamorphisme, se trouvent en correlation parfaite avec le degre de carbonification de la vitrinite (tabl. 2) (fig. 5, 6). Institutul Geological României igr/ 9 LE METAMORPHISME DES CHARBONS DES CARPATHES MERIDIONALES 99 Fig. 5 — Vitrinite fragmentee et cimentee du quartz epigenetique et de la pyrite. Pregheda-Banat. section polie, N II, X 80. Fig. 6 — Greș quartzeux ă Fillite/muscovite sur des fissures et en nids. Pregheda-Banat, lame mince, N +, X 100. Institutul Geologic al Românie 100 GH. POPESCU et al. 10 TABLEAU 2 La relation entre la refletivite (Umax en air), l’espace interreticulaLre(d0(>.2) des phases de tran- sition de charbons â graphite-mineraux silicaUs, indicateurs des zones, stades pelrogenftiques (Carpathes Meridionales) Rang des charbons Rmax air 552 m 0/ /o ^002 (R) ■ Mineraux silicates indicateurs Zones: stades petroge- netiques Houille Houille an- thraciteuse 5,3—5,5 8,8-10,1 >3,70 illite/sericite, quartz epigânelique Diagenese Anthracite 13,8-14,2 3,43-3,59 pyrophyllitc, paragonite/muscovitc chloritoide Anchim6ta- morphisine Graphite >16* 3,36 muscovitc, biolitc Metamor- phisme * Valeurs determinees en huile Conclusions Les charbons des Carpathes Meridionales apparaissent dans des formations sedimentaires afferentes au domaine danubien et au domaine getique et dans des bassins post-tectoniques. Les periodes ou les char- bons se sont accumules en importantes quantites ont ete le Carboni- fere, le Lias et l’Oligo-Miocene. Les caracteristiques petrographiques et optiques quantitatives (R) et roentgenostructurales differencient d’une part les charbons d’âge liasique, en fonction de la position de la formation hote dans l’autoch- tone danubien, et relevent d’autre part le caractere similaire en ce qui concerne les charbons du Carbonifere tant du domaine getique autant que du domaine danubien. Cette comparaison est deduite des conditions geologiques essen- tiellement differentes ou se sont formes les charbons du Carbonifere — bassins limniques —, par rapport â ceux liasiques — bassins paraliques. L’evolution geologique ulterieure des formations liasiques â char- bons a conduit ă leur placement dans des sous-unites structurales differentes du domaine danubien, fait qui a determine une differen- tiation des conditions thermiques qui ont conduit ă de differents stades de carbonification de la masse vegetale. La formation de Schela, â l’anthracite, a ete surmontee, â la suite des phases d’orogenese autri- chienne et laramienne, tant par les formations de la nappe de Severin autant que par celles de la nappe getique, â l’epaisseur cumulee qu’on estime â plus de 6 km (fig. 7). Ainsi, la temperature d’approximative- 11 LE METAMORPHISME DBS CHARBONS DES CARPATHES MERIDIONALES 101 ment 200°C caracteristique au moment de la formation de l’anthracite et du pyrophyllite (Popescu, Constantinescu, 1982) a ete atteinte dans les conditions d’une marche geothermique normale (33m/l°C). 2 Fig. 7 — Coupe schematique montrant l’evolution tectonique des Carpathes Meri- dionales pendant le Senonien-Paleogene (d’apres Codarcea, 1940). 1, zone de Svinița-Svinecea avec les gisements de Cucuiova-Baia Nouă et Biger- Pregheda ; 2, formation de Schela. BIBLIOGRAPHIE Bițoianu C. (1971) La flore du Carbonifere superieur de la Roumanie. Congr. Intern. Stratigr. Geol. Carbonifere, 105-107, Krefeld. Codarcea AI. (1940) Vues nouvelles sur la tectonique du Banat meridional et du Plateau de Mehedinți. An. Inst. Geol. Rom., XX, București. Diessel C. F. K., Offler R. (1975) Change in Physical Properties of Coalfield with Grade of Metamorphism. N. Jb. Mineral, Nb, 1, 11-27. Kisch H. I. (1974) Anthracite and Metaanthracite Coal Ranks Associated with “Anchimetamorphism” and “Very Low-Stage” Metamorphism. Konikl. Ne- derf. Akadem. Wetenchappen Proced., Ser. B, 77, Amsterdam. Kwiecinska B. (1980) Mineralogy of Natural Graphite. Prace Mineralogiczne, 67. Mateescu I. (1962) Studiul petrografic al cărbunilor din bazinul Lupac. An. Corn. Geol., 32, 481-527, București. — (1964a) Studiul petrografic al cărbunilor de la Lupeni. An. Corn. Geol., 34, 2, 248-295, București. — (1964b) Studiu asupra metamorfismului cărbunilor de la Baia Nouă, bazat pe considerente petrografice și chimice. St. tehn. econ., A/6, 5-57, București. Mutihac V., Popescu C. Gh. (1982) Sur le caractere anchimetamorphique de la formation de Schela des Carpates Meridionales centrales. Rev. roum. geol., geophys. geogr., Geol., 2, 47-56, București. Năstăseanu S. (1978) Considerations preliminaires sur l’existence d’un systeme de nappes alpines dans la zone de Reșița ă Lupac (Banat). D. S. Inst. geol. geofiz., LXIV, 89-106, București. Popescu C. Gh.. Tatu M., Damian Gh. (1982) La refletivite et les caracteristiques rontgenostructurales de l’anthracite de la formation de Schela. Anal. Univ. București, Geol., 13-20, București. Răileanu Gr. (1953) Cercetări geologice în regiunea Svinița-Fața Mare. Bul. șt. Acad. R.P.R., 2, 2, București. — Grigoraș N., Oncescu N., Plisca T. (1963) Geologia zăcămintelor de cărbuni, cu privire specială asupra teritoriului R.P.R. Edit. tehn., București. Institutul Geological României Institutul Geological României Petrologie—Mineralogie CONTINUITY, PERIODICITY AND EPISODICITY IN MAGMA GENESIS PROCESSES ASSOCIATED TO THE CLOSING OF THE ALPINE OCEAN IN THE CARPATHIAN AREA BY DAN RĂDULESCU 1 The incompatibility between Stille’s concept regarding the evolu- tion of orogeny and associated magmatic processes — which assumes the alternation of short periods of orogeny and magmatic activity with long quiet periods — and the model of global tectonics — which implies the continuous movement of lithospheric plates and the continuity of associated processes —have been noticed and commented upon as early as the seventies (Evernden, Kistler, 1970). As regards, for example, the North American Cordillera it was shown that the periodicity of tecto- genesis and of magmatic activity was apparent ; these were characterized by episodicity only in places, but they belonged to phenomena essen- tially marked by continuity along the continental margin (Gilluly, 1973). In order to account for the discontinuity of magmatic activity in time and space (along the plate margin) the following hypotheses are stated : (a) the occurrence of several plates subduction-related to the North American Plate, which led to (b) variations of compositions of subducted material and (c) variations of subduction velocity in different sectors of continental margin ; it is to note that at least the former category of variations may oecur within a single plate too ; (d) variations of features of subducted lithosphere or of the upper mantie in which subduction takes place ; (e) variations of depth of low velocity zone of seismic wave propagation (LVZ), which could have stimulated or at- tenuated the magma genesis process. In the Carpathian area — especially in the East and South Car- pathians and Apuseni Mts — the tectogenesis induced, at the end of Mesozoic and beginning of Tertiary, by the collision of Euroasiatic plate with the plates in the south-west and south is systematized in two major deformation phases : Dacidic and Moldavian phases. The magmatic activity brought about by collision-related subduction has been delimited, for a long time, into “Upper Cretaceous-Paleocene 1 University of Bucharest, Department of Mineralogy, Bd. Bălcescu 1, Bu- charest. 104 D. RĂDULESCU 2 magmatic activity” (corresponding to the former “banatites”) and “Neo- gene volcanic activity”. Later on, the former was divided into a Turo- nian-Senonian stage, characterized by andesitic associations and a Paleocene one, characterized by granodioritic associations ; the latter was divided into a Lower Badenian stage and an Upper Badenian- Pliocene stage, characterized by slightly different features in different regions ; the Neogene volcanism exhibited activity “phases”, with no evidence of their length nor of the quiet periods between. The dating of these stages was exclusively based on stratigraphic criteria, because of which the continuity of magmatic activity was never possible to be discussed in detail. The main idea, unanimously accepted and clearly discussed, pointed to an important discontinuity — cor- responding to the Eocene, Oligocene and lowermost Miocene, that is ca 15-ca 18 m.y. B.P. — between Upper Creteaceous-Palogene magmatic activity and Neogene volcanic activity. Although the stratigraphic image could account for the continuity of magmatic activity within each stage, it is quite obvious that as far as the tectonic activity was thought to occur during short stages delimited by quiet periods. the associated magmatic activity was characterized by periodicity. Thus, the major discontinuity was implicitly accompanied by two other ones, less im- portant, between Upper Cretaceous and Paleocene and Lower Badenian and Upper Badenian respectively. The idea of periodicity of magmatic activity was generated mainly by the insufficient Information about the age of rocks ; by the lack of radiometrie determinations, some other facts added. The increasing number of mining and drilling works carried out in the last 20-30 years has revealed the ignoring of the products of subduction related magmatic activity ; in several Neogene volcanic areas, there are complete'ly covered subvolcanic bodies the age of which was proved — by recent radiometrie determination — to be different from the age of volcanic rocks, generally greater than the latter. Thus, the lower limit of Neogene volcanic activity is still a problem as far as it has been stated by taking into account the age of rocks emplaced under subaerial conditions only ; this problem arose many years ago and remained unsolved in the Țibleș and Rodna Mts’ in connection with the age of some subvolcanic bodies related, in outerops, to Paleogene rocks only. Another cause was the ignoring of the true relations be- tween magmatic rocks and magma generating subduction processes and especially the ignoring of the fact that during some periods and in some secțors the compression generated oceanic lithosphere-oceanic lithosphere subduction : the lack of magmatic products, on the continent, during some periods and in some sectors, was attributed to the complete cessation of magmatic activity, by omitting the traces of this activity present in basin deposits of appropriate age and îocation. It is also to note the rather late demonstration of the fact that the oceanic basin corresponding to North and East Carpathians closed gradually from NW to SE — and therefore. the subduction. the magma generation processes and the emplacement of rocks had a similar evolution — and thus favoured the interpretation of age differences among rocks from different sectors as products of independent activity “phases” or Ja Institutul Geologic al României iGRy 3 MAGMA GENESIS PROCESSES AND THE CLOSING OF THE ALPINE OCEAN 105 “stages”. Finally, one should mention that due to the presence in the Carpathian area of two oceanic basins — one corresponding to the East and South Carpathians and one to the West Carpathians (Fig. 1) — 0 Lt «00 km —L. ---------------> Fig. 1 — Sketch of geological structure of Carpathian area and its evolution during the Alpine time (acc. to Rădulescu, Săndu- lescu, 1973, and Săndulescu, 1980). 1, inner zones ; 2, outer zones (flysch) : a, outer Dacidic flysch ; 3, molasse; 4, posttectonic formations and foreland areas ; 5, mafie and ultramafic rocks : a, Transylvanian Nappes ; 6, Upper Cretaceous-Paleocene igneous rocks ; 7, Tertiary volcanic rocks ; 8, oceanic lithosphere : a, in consumption area ; 9, oceanized lithosphere : a, in consumption areas ; 10, continental litho- sphere ; 11, location of sections. A, Trias-Neocomian ; B, Meso- cretaceous : C, C', C", end-Senonian ; D, Actual. 106 D. RADULESCU 4 with different evolution, was created the impression of lack of magmatic aetivity during certain periods and in some sectors ; in fact, the dif- ferences which influenced the evolution of magmatic processes concerned but the compression and the location of subduction areas. The oc- currence of the two basins and of the two subduction areas does not impede on treating the above-mentioned problem in common for all the magmatic processes associated to subduction during Alpine time in the Carpathian area, as everything was generated and controlled by a unique phenomenon all over the area, namely the compression of oceanic basins between the Euroasiatic Plate and the plates adjacent to its south-western extremity. Recent radiometric determinations have allowed the specification of the age of rocks under discussion and have led mainly to stating some new stages of magmatic aetivity associated to subduction during Alpine time {Lemne et al., in press). By using all age determinations at hand (Fig. 2) 2 one rnay show that, on the whole, the magmatic processes associated to subduction during Alpine time were characterized by continuity and the stages identified represented intensifications as part of a “permanence”. First, it is to note the lack of any discontinuity in both the Upper Cretaceous-Paleocene and the Neogene magmatic aetivity. Around the moment 65 m.y. B.P. the frequency of age values is identical with the one corresponding to the whole Upper Cretaceous-Paleocene mag- matic aetivity, while the time interval of about 3-18 m.y.B.P. included no gap, supporting the perfect continuity of rock formation processes in both cases ; if this was easy to foresee in the case of Neogene volcanic aetivity, which could not show but very reduced discontinuity. it is significant to note that the Upper Cretaceous-Paleocene time is remarkably covered by age values of a time interval considered to correspond to a discontinuity. A second remark concerns the time interval ca 18-ca 55 m.y.B.P. corresponding to the “quiet” period between Upper Cretaceous-Paleo- eene magmatic aetivity and Neogene volcanic aetivity. This interval includes less values as compared to those prior or posterior to it ; however, the values are numerous enough and homogeneously spread, fact which shows that the 40 m.y. interval considered to correspond to the “quiet” period is far from marking the cessation of magmatic aetivity. It is probable that the number of values will increase in the future, on the one hand by discovering new rock bodies of this age and on the other hand by finding out that the rocks assigned either to Neogene volcanic aetivity or to Upper Cretaceous-Paleocene magmatic aetivity exhibit, in fact, intermediate radiometric ages. In the case a longer interval of 5 m.y. is considered to represent a “break” of magmatic aetivity, then in the Carpathian area we find only the situation of this kind between 32.5 and 38.8 m.y.B.P. The distribution of values between ca 18 and ca 55 m.y.B.P. shows that this is not a simple decrease of the discontinuity interval length from ca 40 m.y. to 6-7 m.y. but it is due to the inaccurate study of reality. One rnay thus infer that between Upper Cretaceous-Paleocene magmatic Institutul Geologic al României \jGgy 5 MAGMA GENESIS PROCESSES AND THE CLOSING OF THE ALPINE OCEAN 107 activity and Neogene volcanic activity there is no discontinuity at all, but only an important decrease of intensity. Fig. 2 — Distribution of age of rocks asso- ciated to subduction in the Carpathian area, between 0 and 150 m.y.B.P. W, E, subduction asso- ciated rocks in the western and eastern basins. The third remark to be made as a result of radiometric deter- mination concerns the existence of intrusive calc-alkaline rocks of acid- intermediate Chemical nature which belong obviously to subduction magmatic activity, older than the lower accepted limit of Upper Creta- ceous-Paleocene magmatic activity ; however, it is to note a “dis- continuity” of ca 10 m.y. between ca 88 and ca 98 m.y.B.P. The 108 D. RĂDULESCU 6 measured values regard, with a sole exception, the products associated to subduction in the eastern basin and reach ca 130 m.y., being homo- g'eneously distributed between ca 100 and ca 134 m.y.B.P. Thus, it is possible that the magmatic activity started, episodically and with low intensity, just from the beginning of compression, corresponding to the Austroalpine phase (intra-Barremian) which was not completely lacking in magmatic activity as it had been considered so far (Rădulescu, Săn- dulescu, 1980) ; moreover, the values exceeding 120 m.y. arise the question whether magma genesis and implicitly the compression started as far back as the end of Neocomian. The settling of compression regime as far as the end of Neo- comian is also accounted for by other two remarks. On the one hand, it is to note the occurrence of “island arc” products within the Mureș ophiolitic zone (Savu, 1976) ; their radiometric ages, although of ca 66 m.y. — corresponding to the lower part of the interval when igneous rocks generated by subduction were massively emplaced in the continental lithosphere of central and northern parts of the Apuseni Mts — extend to about 122 m.y. and show that at the upper boundary of Neocomian compression had started in the Carpathian area and generated in the western basin an oceanic lithosphere-oceanic litho- sphere collision and subduction — with an island arc formation — before the appearance of a subduction area at the margin of continental lithosphere and the emplacement of magmas in it. On the other hand, radiometric ages of 120-125 m.y. reported for some granitoids in the South Carpathians (Bîrsa Fierului) and considered to represent defor- mation stages, indicate a tension and compression regime, too. The special attention paid separately to the products associated to each of the two basins leads to a fourth remark : most of time, the magmatic activity progressed concomitantly in the two areas ; this demonstrates the simultaneous occurrence of two subduction areas at the margin of continental lithosphere of two microplates and implicitly the presence of the same process of compression all over the Carpath- ian area. There are few instances in which the magmatic activity took place in only one of the two zones. The most important example of this kind is given by the already mentioned magmatic activity earlier than ca 100 m.y.B.P. ; the other ones corresponding to the intervals of ca 18-ca 25 m.y.B.P., ca 32-ca 42 m.y.B.P., ca 23-ca 29 m.y.B.P. and ca 52-ca 59 m.y.B.P. could stand for an insufficient Information or could be accounted for by the statement below. Although there existed two oceanic basins and several microplates, the lithospheric compression in this area of the Earth, from Mesozoic to Tertiary, was obviously a unitary phenomenon ; formerly, this is to be considered as a whole and secondly independently foi' each of the two basins. It is absolutely possible that the two basins reacted at various moments either similarly or differently to the general tension. Thus, in one basin could be active a subduction zone situated at the margin of the continental block, while in the other one compression could generate oceanic lithosphere-oceanic lithosphere collision and sub- JA Institutul Geologic al României 16 Ry 7 MAGMA GENESIS PROCESSES AND THE CLOSING OF THE ALPINE OCEAN 109 duction inside it ; or even at certain times tension could produce the compression of one of the two basins, while the other one was inactive. In case this is true, the relationships between the age of igneous rocks emplaced in and on the continental lithosphere and the continuity of subduction magma genesis and emplacement — on the whole and in each basin — should be considered from a different point of view : the absence of rocks emplaced in and on the continental lithosphere at a certain time and in a certain area does not necessarily mean the cessation of magmatic activity, of subduction or of compression ; this situation should be viewed for both basins by taking into account the possibility of subduction processes inside them and not only at their margins. By examining the timing of subduction relatea magmatism during the Mesozoic and the Tertiary in the Carpathian area the following main ideas arose : 1. The lithospheric compression of present-day Carpathian area was continuous, starting from the end of Neocomian to the complete consolidation of the area. It occurred differently in different zones and at different times : simultaneously in both basins or predominantly in one of them, at certain times ; this was due either to the same process — subduction at the margin of continental lithosphere — or to different ones — coexistence of the previous one with oceanic litho- sphere-oceanic lithosphere subduction. Consequently, compression is not always similarly reflected by deformation of sedimentary formations. 2. Subduction associated magmatic processes were continuous, on the whole, but (a) obvious intensity variations and (b) variations re- garding their location and the location of their products are to be noted ; the variations are due to the different ways compression proceeded. The note presented above is based on both published papers and several unpublished age determinations made by E. Călinescu (1976, 1977, 1978, 1979), N. losipenco (1980, 1981), M. Lemne (1975, 1976, 1977, 1978, 1979, 1980, 1983). S. Mînzatu (1977, 1980), O. Romanescu (1977, 1978, 1979, 1980, 1983), M. Soroiu (1974), A. Tănăsescu (1975, 1977, 1978, 1979, 1980, 1983), E. Vîjdea (1975, 1976, 1977, 1978, 1979, 1980, 1983) during investigations carried out together with A. Ștefan (1983), T Berza (1980), M. Borcoș (1977, 1978, 1979, 1980, 1933), G. Is- trate (1977). H. Savu (1983), D. Russo-Săndulescu (1980, 1983), I. Tiepac (1977), G. Udubașa (1977, 1983) ; most of these reports are to be found in the Archives of the Institute of Geology and Geophysics in Bucharest. 2 Figure 2 does not show the frequency of each value, so that the con- clusions inferred are exclusively related to the continuity of magmatic processes and not to subordinate ones, such as their intensity. Institutul Geologic al României 110 D. RADULESCU 8 REFERENCES Bagdasarian G. P. (1972) Despre vîrsta absolută a unor roci eruptive și meta- morfice din masivul Ditrău și Munții Banatului din România. St. cerc, geol., geofiz., geogr., Geol., 17/1, București. Cioflica G., Lupu M., Nicolae I., Vlad S. (1980) Alpine Ophiolites of Romania : Tectonic Setting, Magmatism and Metallogenesis. An. Inst. geol. geofiz., LVI, București. Evernden J. F., Kistler R. W. (1970) Chronology of Emplacement of Mesozoic Batholithic Complexes in California and Western Nevada. U. S. Geol. Surv., Prof. Pap., 623. Gilluly J. (1973) Steady Plate Motion and Episodic Orogeny and Magmatism. Geol. Soc. Am. Bull., 84. Lemne M., Vâjdea E., Borcoș M., Tănăsescu A., Romanescu O. (1984) Des datations K-Ar concernant surtout les magmatites subsequentes alpines des Monts Apuseni. An. Inst. geol. geofiz., LXI, București. Rădulescu D., Pătrașcu St., Bellon H. (1972) Pliocene Geomagnetic Epochs : New Evidence of Reversed Polarity Around the Age of 7 m.y. Earth Planet. Sci. Lett., 14. — Săndulescu M. (1980) Correlation des phases de deformation, de metamor- phisme et de magmatisme dans les Carpathes. XXVie Congr. Geol. Intern. Coli. C 5 (Mem. B.R.G.M., 115), Paris. Savu H. (1976) Considerations on Display Conditions and Evolutions of the Alpine Ophiolitic Magmatism of the Mobile Mureș Zone (Apuseni Mountains). Rev. roum. geol., geophys. geogr., Geol., 20, 1, București. Institutul Geological României Petrologie-Mineralogie NEOCRETACEOUS-PALEOGENE SUBDUCTION IGNEOUS ROCKS IN THE ROMANIAN CARPATHIANS — MUTUAL RELATIONSHIPS, SUCCESSION AND AREAL DISTRIBUTION BY DOINA RUSSO-SĂNDULESCU ', ELEONORA VÂJDEA ', ANCA TANASESCU1 Introduction These last years important details have been supplied regarding the petrology and the age of the Carpathian Neocretaceous-Paleogene igneous rocks, generally called banatites. It is to note here that the collective term of “banatites” proposed by Cotta (1865) for a group of rocks rather varied from mineralogic and structural view points, most of them granodiorites, was subject to controversed evolution ; some specialists defined them from strictly petrographic point of view, while others regarded them as an Upper Cretaceous-Paleocene petro- graphic province developed in the western part of Romania, south of the Danube in Yugoslavia and farther to the Balkans. Recently, some scientists have delimited the older extrusive products from the younger intrusions. One often mentions the “Laramian igneous rocks” which stand for a wider time interval ; in our opinion, this term is however inadequate, as in the main it relates the subsequent igneous rocks, placed within a wider time interval, to a stage of tectogenesis (deform- ation of crust by compression) which corresponds to a relatively short time interval, thus leading to the wrong assignment to syncinematic magmas. Finally, it is to consider Cotta’s definition and to adopt the term of banatites as more adequate from petrologie point of view and deprived of restrictions as regards their assignment to the time intervals. The occurrences of Neocretaceous-Paleogene igneous rocks in out- crops, boreholes or disclosed by geophysical. researches (Visarion, Săn- dulescu, 1979) as well as their location with regard to the major tec- tonic units of the Romanian Carpathians allow their assignment to two big zones : (1) the South Carpathians, where they are related genetically to the oceanic crust consumption in front of and below the Getic Domain and (2) the Apuseni Mts, where they are related to the oceanic crust 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. Institutul Geological României 112 D. RUSSO-SĂNDULESCU et a!. consumption in the Transylvanides (Rădulescu, Săndulescu, 1973 ; San- dulescu, 1980). Several granitoid intrusions, which either cross or occur in the immediate neighbourhood of ophiolitic complexes (in the South Apu- seni Mts or distinguished on magnetic maps below the molasses of the Pannonian Depression) are uncertain as regards both their location and age (PI.). Within each of the two distinct zones (South Carpathians and Apuseni Mts) volcanic activity and intrusive processes took place. The age of intrusions was considered posterior to volcanics, according to the succession relationships in the Rusca Montană basin in the Poiana Ruscă Mts (Giușcă et al., 1966 ; Krăutner, Krăutner, 1972). In the Apuseni Mts, the age of intrusions was similarly considered, although the partly similar mineralogical and chemical composition of volcanics and plutonics (Istrate, 1978 ; Ștefan, 1980) as well as the vclcano-plutonic complex in Vlădeasa (Giușcă et al., 1969) account for the relatively simultaneous presence of extrusive and plutonic processes. The intrusive processes within Neocretaceous-Paleogene igneous rocks surpassed the volcanic activity, fact which calis for clearing up the problem related to the occurrence of some unconsanguineous mag- mas all over the investigated time interval. Thus, the study of some composite massifs such as Bocșa and Surduc (Russo-Săndulescu et al., 1978, 1983b) as well as the examination of the K/Ar radiometric ages obtained for these plutons allowed the elaboration of a model (Russo- Săndulescu et al.. 1983a), the validity of which is discussed upon in the following pages referring to the banatitic rocks in the Romanian Carpathians. Neocretaceous-Paleogene Igneous Rocks in the South Carpathians An outlook on their occurrence (PI.) points to the prevalente of plutonic rocks in the western, innermost part of Median Dacides, main- ly within the Supragetic Nappe area or exceeding a little the front of this nappe. “the area of plutonic banatites” (Russo-Săndulescu, Berza, 1977). However, the volcanic rocks occur in the largest areas of the Getic Nappe, just like “hypabyssal banatites”, namely within an outer area as compared to the South Carpathian structure. The study of time and space relationships as well as the petro- chemical composition of banatites from the plutonic area of the South Carpathians point to two distinct magmatic stages : 1. Coniacian-Maastrichtian stage (K/Ar ages of 87-68 m.y.), re- presented by complex intrusions which form big plutons (Bocșa 1 and Bocșa 2, Surduc — Russo-Săndulescu et al., 1978, 1983b) and small dykes in places. The early pulses of gabbroic magma are supposed to have started their evolution at greater depth, under the conditions of a relative “tectonic quiescence”, pointed out by the occurrence of layered gabbro- norite and anorthosite nodules, evincing inițial cumulate crystallization. The basic magmas which generated these rocks characterized by pri- mitive chemistry (SiOo — 40-45% and MgO — 7-14% at Surduc — Institutul Geologica! României 3 NEOCRETACEOUS-PALEOGENE SUBDUCTION IGNEOUS ROCKS 113 Russo-Săndulescu et al., 1983b) could be considered as the least modified meltings. The repeated magma injections, or perhaps only the mixing up of inițial magma and some locally fractioned “lots” determine at the present-day level of the intrusion an irregular distribution of anorthosite and gabbronorite nodules or only of cumulate crystals (basic euhedral plagioclase or corroded basic plagioclase nuclei, elino- and orthopyroxene), characterized by a new type of differentiation (?), Fig. 1 — Histogram of K/Ar isotopic age ana- lyses of banatitic rocks during the Conician- Maastrichtian (1) and the Maastrichtian-Eo- cene (2) in the South Carpathians. K/Ar age (m.y.) "schlieren”-like, varied as regards their size and chemical-mineralogical composition (gabbroic, monzodioritic, monzonitic and even sienitic). The alkaline potassic nature of magmas is accounted for by the occurrence of biotite and potash feldspar in the gabbroic schlieren as well as by the occurrence of potassic sienites (which correspond chemically to shoshonites). As regards these former intrusions, already described (Surduc, Bocșa 1 and Bocșa 2 types), the apparent K/Ar ages corresponding to the Coniacian-Maastrichtian interval and culminating between 75-65 m.y. have been reported (Fig.-1). The spațial distrubtion of alkaline potassic intrusions from Surduc to Hăuzești, generally follows the South Carpathian bend and they occur in the innermost areas as compared to the supposed subduction paleoplane (Rădulescu, Săndulescu, 1973 ; Săndulescu, 1980). 2. Maastrichtian-Eocene stage (K/Ar ages of 65-42 m.y.), marked by a different spațial distribution, following a north-southward line, is characterized by big plutonic intrusions in the north and the apo- physes of a pluton in the south (eastern Bocșa or B3, which due to a younger tectonic contact occur to the east of B^ and B2 intrusions ; 8 — c. 667 114 D. RUSSO-SANDULESCU et al. 4 Ocna de Fier-Dognecea ; Oravița-Moldova Nouă), to the east of the previously described plutons. Considering that the second stage intrusions occur in the area of former banatitic igneous rocks (Coniacian-Maastrichtian, as for example at Surduc), then the Maastrichtian-Eocene banatites cover a wider area, both in the Supragetic and Getic nappes. The petrographic and Chemical features as well as the field relation- ships within the plutons Bocșa 3, Ocna de Fier-Dognecea, Oravița- Ciclova-Moldova Nouă have shown that within the typical calc-alkaline Maastrichtian-iEocene stage, the intrusions exhibit multipulse beha- viour (Russo-Săndulescu et al., 1984). Thus, were reported a stage of precursory dykes of basic nature (called stage Bocșa 3.1.) and a stage of emplacement of big granodioritic plutons (stage Bocșa 3.2). It is to note the Chemical and mineralogica! homogeneity within granodioritic plutons, which obviously marked most descriptions of the banatitic province of Romania. The last products of the Maastrichtian-Eocene stage are represent- ed by late, vein-like differentiates (rhyolites, dacites, andesites in places). These dykes cross the granodioritic plutons thus accounting for the persistence of plutonic processes at greater depths than the present-day levels of intrusion'emplacement. On the histogram of Figure 1, this second stage in the South Carpathians covers the Maastrichtian-Eocene interval, its maximum being located between 55-45 m.y. According to individual apparent age values, some bodies (precursory basic dykes) seem to have been em- placed prior to the end of igneous rocks evolution during the Coniacian- Maastrichtian stage (about 70 m.y.). Therefore the relationships among banatitic plutons are not simple at all, as far as sequences of veins belonging to the preceding stage (characterized by chemistry obviously typical of the last acid differentiates) may occur at the same time with the precursory basic dykes of the following stage. Neocretaceous-Paleogene Igneous Rocks in the Apuseni Mountains In the Apuseni Mts one distinguishes a Southern area in which occur ophiolite nappes — the “Simic Metaliferi” Mts which belong to the Transylvanides (Săndulescu, 1975, 1980) ; in the west, this zone bends southwards below the Pannonian Depression (Visarion, Săndulescu, 1979). Some of the plutonic bodies, previously considered to stand for banatitic magmatic activity (Săvîrșin, Cerbia), have not been attested by the geochronological study. By taking these into account, as well as the less clearly stated position against the subduction paleoplane, the values obtained for the post-ophiolitic igneous rocks in the Simic Metaliferi were not presented on the histogram regarding the Apu- seni Mts. In the Northern Apuseni Mts the Neocretaceous-Paleogene igneous rocks occur as intrusions of different shapes and sizes in the Gilău and Bihor Mts where they pierce the crystalline schists and the sedi- mentary covers of several tectonic units : Bihor Unit, Codru nappe Institutul Geological României 5 NEOCRETACEOUS-PALEOGENE SUBDUCTION IGNEOUS ROCKS 115 system and Biharia nappe system. The greatest part of banatitic rocks crop out in the Vlădeasa massif of the Apuseni Mts. Most references to the banatitic sequence imply a parallel with the volcanic and plutonic series reported from Vlădeasa (Istrate, 1978 ; Ștefan, 1980). Although the characteristic aspect of the Vlădeasa massif is influenced by the occurrence of acid volcanics in varied facies, an ignimbrite rhyolite formation, earlier andesite and dacite flows, as well K / Ar age ( m.y.) rites, mainly granodiorites, tonalites and monzogranites do also occur ; microgranitic and aplitic rocks pierce the entire complex as last dif- ferentiates. A more general systematization of the above cited authors sup- poses a former magmatic cycle mainly volcanic and subvolcanic (ande- sites-dacites-rhyolites) followed by a cycle represented by intrusions (diorites-granodiorites-granites). The main features of Neocretaceous-Paleogene magmatic activity in the Northern Apuseni Mts are due to the presence of successive magma pulses, pointing to both the differentiation into intermediate magmatic chambers situated below the emplacement level of present- day intrusions and the repetition of some “cycles” of typically calc- alkaline rocks. It is also to note as characteristic feature, the close relationships between volcanic and plutonic formations, of comagmatic nature, temporally and spatially associated, and forming the Vlădeasa volcano-plutonic Complex (Giușcă et al., 1969), as well as the presence, in this same'area of the ignimbritic formation (Istrate, 1978; Ștefan, 1980). By taking into account the above mentioned features, the radio- metric ages reported from the Northern Apuseni Mts have been cumu- lated on the histogram of Figure 2, on which one may note a long time Institutul Geological României 11G D. RUSSO-SANDULESCU et al. 6 interval during which the Coniacian-Eocene magmatic activity took place (K/Ar- age of 90-42 m.y., Lemne et al., 1981) with a wide maximum between 75-55 m.y. According to the model proposed by Rădulescu and Săndulescu (1973), the entire banatitic magmatic activity in the Northern Apuseni Mts was considered to have resulted from the oceanic crust consumption in the Transylvanides, the remnants of which are still preserved in the major Tethysian suture in the Simic Metaliferi area (Săndulescu, 1980). This area is situated between two big groups of Carpathian tec- tonic units and delimits the Neocretaceous-Paleogene igneous rocks presented above. Some of the main features which point to similarities or dif- ferences between the two large areas of Neocretaceous-Paleogene mag- matic activity in the Romanian Carpathians are : — All the banatites in the Northern Apuseni Mts cross the Codru and Biharia nappe systems of pre-Gosau age, probably intra-Turonian (Mediterranean). In the Trascău Mts there is an area in which a Neo- cretaceous (?) volcano-sedimentary formation and probably Laramian nappes are crossed by banatitic dykes, which point to an intrusive activity subsequent to the nappes (Russo-Săndulescu, Berza, 1976). — South of the Simic Metaliferi, the South Carpathian banatites are located within a more externai group of tectonic units, Crossing the Supragetic nappes, partly of Mesocretaceous age with Laramian re- working, and the Getic Nappe initiated during the Mesocretaceous and completed during Laramian tectogenesis. From this point of view, in both areas of banatitic magmatism, it is to note that they are sub- sequent to the nappes which they cross. Another similar feature of banatites from the two zones is represented by the long time interval during which the magmatic activity took place, that is Senonian-Eocene (according to K/Ar age of 90-42 m.y.). It is to mention two maxima in the South Carpathians, and only one maximum value in the North- ern Apuseni Mts, that is more homogeneous and on a wider time interval. Finally, the occurrenee of an ignimbrite formation both in the South Carpathians (in the Maastrichtian volcano-sedimentary formation at Poiana Ruscă) and in the Northern Apuseni Mts (Vlădeasa massif), which is prior to some calc-alkaline, generally granodioritic, intrusions, seems to point to an obvious similarity within the Maastrichtian-Eocene stage stated in Banat. As compared to the model of banatitic magma generation in the South Carpathians, in the Apuseni Mts it does not consist of two stages, lacking in the basic magmas with alkaline potassic tendency and the evidence of inițial cumulate crystallization of the first stage. The petro- chemical nature of banatites in the Northern Apuseni Mts is more homogeneous resulting in sequences of calc-alkaline rocks (both volcanic and intrusive) typical of subduction magmas. It is possible that this homogeneity is due to the generation of magmas as a result of oceanic crust consumption in the Tethys Ocean (preserved in the present-day major Tethysian suture — the Transylvanides). Institutul Geological României NEOCRETACEOUS-PALEOGENE SUBDUCTION IGNEOUS ROCKS 117 Nevertheless, in the South Carpathians, although characterized by oceanic crust consumption, this was generated within an intracontinental rift of Afars-Red Sea type (according to the model proposed by Săndu- lescu, 1980, 1983). The consumption of this crust started during Meso- cretaceous tectogenesis and was perfected during Laramian tectogenesis, concomitantly with the end of Getic and Severin nappes overthrusting. This process has led to the appearance, during the first stage (Coniacian- Maastrichtian), of basic igneous rocks and alkaline-potassic differentia- ion products, typical of a distention period, unconsanguineous with the calc-alkaline igneous rocks of the next stage (Maastrichtian-Eocene). Conclusions The Carpathian Neocretaceous-Paleogene igneous rocks are related to oceanic crust consumption by means of processes similar to clas- sical subduction, while the igneous rocks resulted, both volcanic and intrusive, are the calc-alkaline types characteristic of subduction areas (andesite-dacite-rhyolite assemblage or their plutonic correspondents). The occurrence in the Banat region of some igneous rocks peculiar from both structural and petrochemical points of view (gabbronorites and anorthosites with layered structure, basic rocks with alkaline potas- sic tendency, the differentiates of which show even a shoshonite che- mistry) points to the existence of some unconsanguineous magmas in the same area. However, by taking into account the two maxima corresponding to the emplacement of plutonic intrusions with peculiar petrochemical features, the magma genesis is difficult to be accounted for by the same simple subduction process. As far as the recent studies have not solved yet the problem of the time necessary for the genesis and emplacement of magmas, as compared to the initiation of crust shortening and consumption phenomena, the simple reference to radiometricc ages without taking into account the tectogenetic and magmatogenetic conditions character- istic of each area, or even the structure of each pluton, could lead to conclusions inadequate to the Carpathian area. Thus, it is quite probable that in the South Carpathians, the first magmatic stage (K/Ar age values corresponding to the Coniacian- Maastrichtian) depend on oceanic crust consumption, which started during the Mesocretaceous ; the emplacement of these magmas reached its maximum during the Maastrichtian, in the Getic and Supragetic nappes (in this region the Laramian tectogenesis had started much earlier). The second maximum, between 55-45 m.y., took place rather late as compared to Laramian movements (just like it is the case with the first stage as compared to Mesocretaceous movements) in the South Carpathians. The data above lead to a general conclusion on the emplacement stages of Neocretaceous-Paleogene magmas in the Carpathians. By merely taking into account the isotopic K/Ar ages one may infer the apparent continuation of magmatic activity ; however, the study of the 'L Institutul Geologic al României 118 D. RUSSO-SANDULESCU et al. 8 two maxima of South Carpathian banatites corroborated with the characteristic petrology and tectogeneses from this area, reveals the peculiar conditions under which subduction. crust consumption, source areas, genesis and differentiation of magmas took place. REFERENCES Cotta B. (1865) Erzlagerstătten im Banat und in Serbien. Wien. Giușcă D., Cioflica G., Savu H. (1966) Caracterizarea petrologică a provinciei bana- titice. An. Com. Stat Geol., XXXV, 13-45, București. — Istrate G., Ștefan A. (1969) Le complexe volcano-plutonique de la Vlădeasa (Roumănie). Bull. Voie., XXXIII-4, 1118-1127, Napoli. Istrate G. (1978) Petrologie Study of the Vlădeasa Massif (Western Part). An. Inst. geol. geofiz., LIII, 177-297, București. Krâutner H. G., Krăutner FI. (1972) Report, archives of the Institute of Geology and Geophysics, Bucharest. Lemne M., Vâjdea E., Borcoș M., Tănăsescu A., Romanescu O. (1934) Des data- tions K-Ar concernant surtout les magmatites subsequentes alpines des Monts Apuseni. An. Inst. geol. geofiz., LXI, București. Rădulescu D., Săndulescu M. (1973) The Plate-Tectonics Concept and the Geo- logical Structure of the Carpathians. Tectonophysics, 16, 155-161, Amsterdam. Russo-Săndulescu D., Berza T. (1976) Fereastra Boieriște de la Valea Muntelui - Colțești (Munții Trascău). D. S. Inst. geol. geofiz., LXW5, 141-148, București. — Berza T. (1977) O banatitah iz zapadnoi ciasti iujnîh Karpat (Banat). Proc. llth Congr. Carp.-Balk. Geol. Assoc., 271-273, Kiev. — Berza T., Bratosin I., lanc R. (1978) Petrological Study of the Bocșa Banatitic Massif (Banat). D. S. Inst. geol. geofiz., LXIV/1, 105-172, București. — Vâjdea E., Tănăsescu A. (in press) Semnificația vîrstelor radiometrice (K-Ar) obținute în zona plutonilor banatitici din Banat. D. S. Inst. geol. geofiz., LXX/1, București. — Bratosin I., Vlad C., lanc R. (in press) Studiul petrochimic al magmatitelor banatitice de la Surduc (Banat). D. S. Inst. geol geofiz., LXX/1, București. — Berza T., Bratosin I., Vlad C., lanc R. (in press) Studiul petrologie și geo- chimic al banatitelor din regiunea Ocna de Fier-Dognecea (Banat). D. S. Inst. geol. geofiz., București. Săndulescu M. (1975) Essai de synthese structurale des Carpathes. B.S.G.F. (7), XVII, 3, 299-358, Paris. — (1980) Analyse geotectonique des chaînes alpines situees autour de la Mer Noire occidentale. An. Inst. geol. geofiz., LVI, 5-54, București. — (1983) Le probleme de la marge continentale europeenne dans l’areal Car- patho-Balkanique, An. Inst. geol. geofiz., LIX, 199-268, București. — Krăutnei- H. G., Borcoș M., Năstăseanu S., Patrulius D., Ștefănescu M., Ghenea C., Lupu M„ Savu H., Bercia I., Marinescu F. (1978) Harta geologică a R.S.R. Inst. geol. geofiz., București. Institutul Geologic al României ■9 NEOCRETACEOUS-PALEOGENE SUBDUCTION IGNEOUS ROCKS 119 Ștefan A. (1980) Petrographic Study of the Eastern Part of the Vlădeasa Eruptive Massif. An. Inst. geol. geofiz., LV, 207-325, București. — Lazăr C., întorsureanu I., Horvat A., Gheorghiță I., Bratosin I., Șerbă- nescu A., Călinescu E. (in press) Studiul petrologie al rocilor eruptive bana- titice din partea de est a munților Gilău. D. S. Inst. geol. geofiz., LXIX/1, București. — Lazăr C., Bratosin I. (1983) Report, archives of the Institute of Geology and Geophysics, Bucharest. Visarion M., Săndulescu M. (1979) Structura subasmentului depresiunii pannonice în România (sectoarele central și sudic). Stud. cerc. geol. geofiz., 17, 2, 191-201, București. Institutul Geologic al României Institutul Geological României D RUSSO-SĂNDULESCU et al Neocretoceous - Poleogene Subduction Imprim Atol Inst Geol-Geof ANUARUL INSTITUTULUI DE GEOLOGIE SI GEOFIZICĂ. VOL LXIV Institutul Geological României Petrologie-Mineralogie TRENDS OF THOLEIITIC MAGMA DIFFERENTIATION IN THE SHEETED DYKE COMPLEX FROM THE MUREȘ ZONE (ROMANIA) HARALAMBIE SAVU CONSTANȚA UDRESCU VASILICA NEACȘU MARIA STOIAN 1 1. Introduction The observations concerning the differentiation of the basaltic magmas were made since the beginning of this century. From then on, important progresses were made, as today magmas are characterized according to the tectonic setting and their petro- and geochemical features. This paper presents the differentiation of the tholeiitic magma from which the sheeted dyke complex was formed in the Mureș Zone, its Controls and trends. 2. Remarks on the Structure and Petrography of the Sheeted Dyke Complex The sheeted dyke complex (O2) is developed in the Drocea Mts (Fig. 1) on a length of 35 km and a maximum width of 10 km (Savu et al., in ,press ; Savu, 1983, in press a. b). North-westwards it overthrusts a scale of oceanic floor basalts (O^ and together overlap the flysch (JL-CrO. which encompasses the products of a bimodal volcanism. The 0.5-2 m thick dykes consist of basalts, dolerites and spilites, but in the Dumbră- vita-Julița-Lupești region they alternate with dykes of gabbro, ferro- gabbro, granophyre and albite-quartzdiorite which are also pierced by thin dykes of dolerite, ferrodolerite, basalt, gabbroporphyrite and dyke- lets (Rothery, 1983) of hyaloferrobasalt. Dykes and veins of felsite and albitic (trondhjemite) plagiogranite with xhenoliths of basic rocks meta- morphosed in amphibole hornfelses are rarely found. The sheetecl dyke complex was formed during the spreading stage of the Mureș Ocean and its presence is a clear proof that ophiolites 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 2 Enterprise for Geological and Geophysical Prospections. str. Caransebeș 1, 78344 Bucharest. i Institutul Geologic al României 122 H. SAVU et al. 2 1. basalts complex (O|) ; 2, sheeted dyke complex (OJ ; 3, gabbro bodies ; 4. series of island arc volcanics (Jj-Ci’i) ; 5, Stramberg Limestones ; 6, flysch (J^-Crj) ; 7, Upper Cretaceous ; 8, Lower Cretaceous-Paleocene acid intrusions ; 9, Neogene ; 10, Neogene volcanics ; 11, alluvial deposits : 12, overthrust; 13, reverse fault ; 14, fault, Institutul Geological României SHEETED DYKE COMPLEX - MUREȘ ZONE 123 from the Mureș Zone basement appeared in oceanic floor conditions (Savu et al., in press). It is similar to other sheeted dyke complexes in the world, which are considered to be formed in spreading conditions (Coleman, 1977). The rock structures are intergranular, ophitic and hypidiomorphic- granular. The first mineral to crystallize is plagioclase (labrador An 50-70 or albite An 8-10), followed by clinopyroxene, magnetite and ilmenite ; the albitic felsites are an exception, where garlands of elongated crys- tals of clinopyroxene are formed before the albitic mass which en- compasses them. The clinopyroxene is an augite (c A Ng = 44°) rarely diopside and in the albitic felsites a Ti-augite (c A Ng = 47°). Albitic plagiogranites contain a brown-greenish amphibole (c A Ng = 22°). In the granophires, sometimes in the albitic plagiogranites, mirmekitic, rarely micrographic textures are frequent. The presence of the latter ones and of some small interstitial crystals of finely twinned albite of low temperature seem to indicate the inițial existence of a sub- sequently albitized potassium feldspar. 3. Differentiation of the Tholeiitic Magma The parental magma of the sheeted dyke complex was an oceanic floor tholeiitic magma (Fig. 2). The previous researches on the tholeiitic magma 'differentiation have shown that this one had only one trend, according to which the residual magma gradually enriched in iron, alkalis and SiO2 ; thus, a continuous curve is established on a FMA dia- La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb tu Fig. 2. — Chondrite — normalized REE pattems for non-differentiated basic rocks. gram (Wager, Deer. 1939). Our studies on the sheeted dyke complex from the Mureș Zone (Savu et al., in press; 1983 unpublished data) have shown that its rocks can be separated into the following groups3 : 1) non-differentiated basic rocks, 2) differentiated basic (ferrobasaltic) rocks and 3) differentiated acid-albitic rocks (Tab.). These derived from the same tholeiitic magma, formed in a magmatic chamber (MacDonald, 1982) located in the mantie at about 100 km deep under the spreading centre. Their separation was not produced after a monovariable curve, 124 H. SAVU et al. TABLE Chemical composilion of the three groups of shceled dyke rocks (>0 anal.) Oxides and elemcnts Non-differentiated tholeiitic rocks Differentiated basic rocks Differentiated acid rocks SiO2 (%) A12O3 Fe,O3 Feb MgO CaO Na2O K.0 TiO. p2o; Ni (ppm) Co Cr V Sc Zr Y Yb I.a Ba Sr Pb Cu Ga Sn 47 .47 — 51 .75 12.87-15.95 1 .36— 5 .30 3.26- 9.32 6 .10 — 8 .65 7.84 — 12.64 0.86-3.70 0.06- 0.88 0.60— 2.35 0.08- 0.32 30-200 23—55 46 — 565 200-325 28—10 37-200 14—55 1 .7 — 6 .5 <30 12-80 95-240 <2—11 2-52 8 .5-22 <2-3 43 .20-52 .14 10.87-17.73 2.46 — 11.12 3.60 — 14.84 3.22- 6.21 6.49-15.81 2.31- 4.93 0 .05- 1 .30 2.39- 6.95 0.06- 1.64 14 — 127 4-65 1 .5-190 190-900 11-42 54-280 10-87 4.8-10.5 <30 10-110 18-240 <2 — 5 2 .5-53 12-51 <2-7 51.76 — 75 .53 11 .50—14 .11 2 .25- 6 .77 0.61— 9.64 0.21- 2 99 1.58- 7 .03 4 .65— 5 .71 0.05- 3.39 0.34- 3.32 0.12- 0.88 3. 5-18 5 .5 — 22 1 . 5-38 12-210 7.50-26 206-850 60-150 6 . 5 —18 .5 <30-38 <10-60 43-155 <2-23 4 — 32 12-30 <2—4 .5 FcO (tot)/MgO 0 .70-2 .0 2 .0 — 5.85 3.0-18.75 but the tholeiitic magma differentiation had two trends : 1) a trend which led to the enrichment of one part of the magma in iron (Fenner, 1929) and 2) a trend which led to the enrichment of the residual magma in SiO2, alkalis and gas. especialiy dissociated water (Fig. 3). One can notice that on the first trend (a) the differentiation starts from the non-differentiated basic magma and goes towards the FeO corner of the diagram, following a straight line which leads from the basalt- doleritic rocks to ferrogabbros and hyaloferrobasalts. On the second trend (b) the differentiation starts in the separation zone of differentiat- ed basic (ferrogabbroic) rocks from the non-differentiated ones, follow- ing a curve which turns and goes towards the alkalis corner, reaching somewhere lower the FeO-Na2O-f-K2O side. Although the acid-aibitic rocks are maintained in the tholeiitic domain, after its appearance and position, this curve remembers rather the intermediary magmas curve of Izu-Hakone type (Miyashiro, 1975, Fig. 4) ; this aspect would result as well from other geochemical peculiarities of the differentiated acid-albitic rocks. The behaviour of Ti (Fig. 4) as well as that of V (fig. 5) indicate the same two trends of tholeiitic magma differentiation. Institutul Geological României 5 SHEETED DYKE COMPLEX-MUREȘ ZONE 125 Fig. 3 — FeO tot — MgO — Na2O 4- K2O diagram with the separation curve (IB) of tholeiitic rocks from the calc-alkali ones, according to Irvine and Bara- gar (1971). 1, non-differentiated basic rocks ; 2, differentiated basic (ferrobasaltic) rocks ; 3, differentiated acid-albitic rocks ; a, differentiation line of ferrobasaltic magmas ; b, differentiation curve of acid magmas — the legend of this diagram can be used for the others, too. 0.30 0.40 050 0,50 0.70 0.80 0.90 1,00 1.10 1,20 FeOt/reOt-MgO Fig. 4 — TiO2-FeO tot/FeO tot -j- MgO diagram (after Serri and Saitta, 1980). Institutul Geological României 126 H. SAVU et al. 6 SHEETED DYKE COMPLEX-MUREȘ ZONE 127 3.1. Characteristics of the Non-Differentiated Tholeiitic Magma. This magma approximately corresponds to the primary tholeiitic magma (Fig. 3), whose differentiation was possibly very weak. From this one there formed many rocks of the sheeted dyke complex (basalts. dole- rites, gabbros) and evidently those of the basaltic complex (O|). It be- longs țo the “high-Ti” type of magmas (Fig. 4), which according to Serri and Saitta (1980) shows that it was similar to the magma from median oceanic ridges. Within the rocks formed from this magma, the ratio FeO tot/MgO (Miyashiro, 1975) is lower than 2 ; the Na2O content is below 3.70% and that of K2O is seldom highei’ than 0.60%. Because of that the non-differentiated basic rocks are located in the normal tholeiitic field on the diagram in Figure 3, which is to be noticed as well on diagrams foi’ minor elements (Figs. 5-7). The REE content is generally constant and the patterns of these elements are situated on the diagram in Figure 2 between the values of 6.5-20.8 of the rock/ chondrite ratio. 3.2. Characteristics of Differentiated Basic (Ferrobasaltic) Magmas. These magmas represent the differentiated magmas enriched in iron (Fe2C>3 = 2.46-11.12% ; FeO = 3.60-14.84%) and other Chemical ele- ments (Kennedy, 1948) from which ferrogabbros, ferrodolerites and hyaloferrobasalts have resulted. The differentiation of these rocks from the tholeiitic magma is clearly illustrated in the diagram of Figure 3, where they are situated in the tholeiitic rocks field ; they are con- tinuously distributed along the line (a). Besides the iron. these magmas enrich in TiO? (1.28-6.95%), .as it can be noticed in the diagram of Figure 4, as well as in V (Fig. 5). The Co and Sc contents are approxi- mately constant as they show only a weak tendency of decreasing. A very strong decreasing for this group of rocks, as for the other two, is noticed for Ni and especially for Cr (Fig. 6). On the contrary. Zr, Y and Yb show a clear tendency of increase along the whole series of sheeted dykes (Fig. 7). Therefore, the rocks from the ferrobasaltic magmas group occupy on these diagrams as on other diagrams for minor elements, an intermediary position, as they are situated between the non-differentiated basic rocks and that of differentiated acid- albitic rocks. 3.3. Characteristics of Differentiated Acid Magmas. These magmas have resulted from the residual liquid from which there previously separated the Chemical elements which led to the formation of dif- ferentiated basic (ferrobasaltic) magmas. From these magmas there formed some spilitic rocks, albite-quartzdiorites, granophyres, plagio- granites and albitic plagioaplites. The acid magmas gradually enriched in SiO2 (51.76-75.53%) and alkalis, especially Na2O (4.65-5.71%), some minor elements such as Yb, Y and Zr (Fig. 7) as well as gas. They were depleted of Mg, Ca, Fe (Fig. 3), Ti (Fig. 4) and minor elements such as V, Co, Sc (Fig. 5) and Ni, Cr (Fig. 6). The value of FeO tot/MgO ratio is higher than 6. The fact that on all diagrams for minor elements, except that for V, % Institutul Geologic al României igrZ 128 H. SAVU et al. 8 Fig. 6 — Cr, Ni — FeO tot/MgO diagrams. the acid-albitic rocks are situated in prolongation of rock fields from the sheeted dyke complex, no matter if they indicate positive or nega- tive correlations, clearly demonstrates that differentiated acid magmas were separated from the primary tholeiitic magma as the differentiated basic (ferrobasaltic) ones have done, and so they have no other origin. Another argument is the very low content of K2O (< 0.40",.) of these magmas. They show as well the lowest contents of Sr and Ba as com- pared to the whole series of the analysed rocks. Institutul Geologic al României 9 SHEETED DYKE COMPLEX-MUREȘ ZONE 129 FeOtot/MgO Fig. 7 — Yb, Y. Zr — FeO tot/MgO diagrams. Institutul Geological României 130: H. SAVU et al. 10 4. Final Remarks The tholeiitic magma which was formed from the pyrolith ori- ginating in the magmatic chamber located in the mantie (Savu et al., 1981) is differentiated, following the below mentioned line which leads. to the formation of; the three rock groups. Pyrolith -» Primary tholeiitic -> acid magmas magma \ basic (ferrobasaltic) magmas. It is possible that ultrabasic rocks (magmas) from the gabbro- peridotitic complex (O:;) of the ophiolitic series situated in depth would have been first separated from the inițial pyrolith, so that the primary tholeiitic magma got the character of a “high-Ti” magma, SiO2, AI2O3. and CaO saturated, which imprinted from the very beginning its dif- ferentiation trends. As concerns the acid-albitic rocks associated to ophiolites from. Corsica, Ohnenstetter and Ohnenstetter (1980) think that they were formed by imiscibility, a phenomenon that appeared after the beginning. of ferrogabbros crystallization. In the case of the sheeted dyke complex from the Mureș Zone, we can see on the diagram of Figure 3 that the acid-albitic rocks curve (b) is separated from the differentiation line (a) in the same zone where ferrobasaltic magmas start separating from the normal tholeiitic one. The cause of this differentiation consists in the Chemical pecu- liarities of the primary tholeiitic magma, which allow the crystallization first of plagioclase, which determines the enrichment of the residual magma in Fe, Ti, V, Si, Na, lanthanides and other minor elements, as well as gas, especially dissociated water. These substances, by their character and quantities to be found in the residual magma, are in- compatible with the formation of a natural magma. Therefore, the imiscibility phenomenon appears, due to which a ferrobasaltic magma is separated on the one hand, which will be the source of ferrogabbros with concentration of Fe, Ti and V and on the other hand an acid magma, rich in Si, Na and dissociated water which develops as an undercooled magma. In this magma there originated spilites, grano- phyres, albitic plagiogranites and sulphide mineralizations from the- ophiolitic series (Savu, 1973). 3 Rocks (magmas) discrimination method: first there are separated non-differentiated rocks, with FeO tot/MgO < 2, then the basic (ferrobasaltic) differentiated’ rocks with FeO tot/MgO = 2-6, SiO> < 52%, which are enriched in iron, Ti and V on the one hand, and the differentiated acid-albitic rocks with FeO tot MgO > 3. SiO., > 52%, Na-jO > 4%, rich in La, Y, Yb and Zr on the other hand. The orthospilites with Na2O < 4 are situated in the second group, at the beginning. of imiscibility (Fig. 3). 11 SHEETED DYKE COMPLEX - MUREȘ ZONE 131 REFERENCES Coleman R. G. (1977) Ophiolites — Ancient Oceanic Litosphere ? Springer-Verlag, 229 p., Berlin. Fenner C. N. (1929) The Crystallizations of Basalts. Am. J. Sci., 5th Ser. 18, p. 225-253, New Haven, Conn. Irvine T. N., Baragar W. R. A. (1971) A Guide to the Chemical Classification of the Common Volcanic Rocks. Can. J. Earth Sci., 8, p. 523-548. Kennedy G. C. (1948) Equilibrium between Volatiles and Iron Ores in Igneous Rocks. Am. J. Sci., 246, 9i New Haven, Conn. MacDonald K. C. (1982) Mid-Oceanic Ridges : Fine Scale Tectonic, Volcanic and Hydrothermal Processes within the Plate Boundary Zone. Ann. Rev. Earth Planet. Sci., 10, p. 155-190, Palo Alto, California. Miyashiro A. (1975) Volcanic Rock Series and Tectonic Setting. Ann. Rev. Earth Planet. Sci., 3, p. 251-270, Palo Alto, California. ■Ohnenstetter M., Ohnenstetter D. (1980) Comparison between Corsican Albitites and Oceanic Plagiogranites. Archives des Sciences, 33, F 2-3, p. 201—220, Geneve. Rothery D. A. (1983) The Base of a Sheeted Dyke Complex, Oman Ophiolites : Implications for Magma Chambers at Oceanic Spreading Axes. J. Geol. Soc. London, 140, p. 287-296, London. Savu H. (1973) Succession dans la separation des oxydes et des sulfures des magmas ophiolitiques de la zone du Mureș (Monts Apuseni). Rev. roum. geol., geophys., geogr., 17, 1, p. 15-20, București. Savu H.. Udrescu C., Neacșu V. (1981) Geochemistry and Geotectonic Setting of Ophiolites and Island Arc Volcanics of the Mureș Zone (Romania). Ofioliti, 6 (2), p. 269-286, Bologna. Savu H. (1983) Geotectonic and Magmatic Evolution of the Mureș Zone (Apuseni Mountains). C.-B.G.A. 12 th Congr., Bucharest, 1981, An. Inst. geol. geofiz., LXI, București. Savu H., Udrescu O., Neacșu V. (in press) Petrology and Geochemistry of the Sheeted Dyke Complex in the Mureș Zone, Dumbrăvița-Baia-Bătuța-Julita Region (Apuseni Mountains). D. S. Inst. geol. geofiz., LXIX/1, București. Savu H. (in press a) Structural, Petrographic and Geotectonic Study of the Sheeted Dyke Complex from the Mureș Zone, in the Dumbrăvița-Baia-Bâtuța-Julifa Region (Apuseni Mountains). O. S. Inst. geol. geofiz., LXIX/5, București. Savu H. (in press b) The Sheeted Dyke Complex in the Mureș Zone (Apuseni Mountains). Rev. roum. geol., geophys., geogr., Geol., 28, București. Serri G., Saitta M. (1980) Fractionation Trends of the Gabbroic Complexes from High-Ti and Low-Ti Ophiolites and the Crust of Major Oceanic Basins : A Comparison. Ofioliti, 5, (2/3), p. 241-264, Bologna. Wager L. R., Deer W. A. (1939) The Petrology of the Skaergaard Intrusion Kangerdlugssuaq, East Greenland. Medd. on Greenland, 105, 4. Institutul Geological României Petrologie-Mineralogie CHLORITIZATION OF BIOTITES AND ITS BEARING ON K-Ar AGES OF SOME ALPINE MAGMATITES FROM POIANA RUSCA MASSIF BY CAROL STRUTINSKIMARJA PAICA NICOLAE POP - Introduction The present paper deals with 15 K-Ar ages on biotites and their interpretation in view of the fact that in most cases biotites were more or less affected by chloritization. The biotites under consideration were extracted mainly from granodioritic rocks located in the south- western part of the Poiana Ruscă Massif (South Carpathians), where they form several subvolcanic bodies (Fig. 1). which represent the north- ernmost extremities of the Tincova-Krepoljin and Rușchița-Bor bana- titic alignments (Krăutner, Krăutner, 1972), belonging to the Tethyan- Eurasian Metallogenetic Belt (Jankovic, 1977). Details regarding pre- paration techniques of the concentrates and determination methods are to be found in Strutinski et al. (in press). K-Ar Diagrams versus Harper Isochrons The determined ages (Tab.) pointed out that, despite the petro- graphic likeness, the igneous rocks of the Tincova and Ruschița groups represent two distinct moments of magmatic activity (Strutinski et al., in press). This situation is obviously illustrated by the K-Ar diagrams (Fig. 2), where it can be seen that the samples are plotted cn two straight lines, corresponding to the two groups of intrusions. On the upper line the granodiorites of the Tincova intrusion (samples 27PR, 29PR, and 31PR), as well as their porphyritic varieties (9PR, 25PR), occurring as dykes (apophyses ?), are figured. On this line a grano- diorite porphyry dyke from Ruschița (sample 5PR) is also plotted, a possible evidence of the first phase of emplacement being active also 1 “Banat” Geological Enterprise of Prospections and Exploration, str. 30 De- cembrie 1, 1650 Caransebeș. 2 Institute of Research, Technological Engineering and Designing for Non- ferrous Ores, str. V. Babeș 62, 4800 Baia Mare. 134 C. STRUTINSKI et al. 2 Fig. 1 — Geologic sketch of the south-western part of the Poiana Rusca Massif showing location of samples radio- chronologically dated. 1, metamorphic basement; 2, Mesozoic sedimentary rocks ; 3 , subvolcanic, mainly granodioritic, intrusive bodies ; 4, Neozoic sediments and alluvial deposits ; 5, faults ; 6, samples. TABLE Analytical data of K-Ar ages on biotites of the intrusive and dyke rocks from the south-iveslern part of the Poiana Pască Massif (South Carpathians)* Sample No. Rock type % K %C** 40Ar rad io-» g/g Age (m.y.) (±1-) 5 PR Granodiorite porphyry 6.61 22 .3 37 .61 80.3±2.4 6 PR Quartz diorite porphyry 4 .69 38.8 26 .63 80.1 ±2 .4 9 PR Granodiorite porphyry 6 .09 23 .6 35 .10 81,3±2.4 13 PR Granodiorite 5 .76 30 .4 30.77 75 . o 2 .3 14 PR Granodiorite 6.97 18.6 34.88 70 ,8±2.1 25 PR Granodiorite porphyrv 5 .68 29.6 32 .92 81 .74- 2 .0 27 PR Granodiorite 7 .035 17 .3 39 .83 80 ,0±2.4 28 PR Granodiorite 5.40 20 .0 28 .26 74.04-2.2 29 PR Granodiorite 6 .54 14 .6 36 .59 79 .0 — 2 .4 31 PR Granodiorite 6.46 15 .2 35 .94 78.5±2.4 32 PR Granodiorite 5.88 13.3 31.29 75 .2±2.3 33 PR Granodiorite 2 .54 27 .5 13.42 74 ,6±2.2 34 PR Granițe porphyry 7.19 20 .4 37 .45 73.6±2.2 37 PR Dacite 4.48 34 .3 22 .05 69 .7±2.1 38 PR Granodiorite porphyry 5.33 21 .3 27 .76 73.6±2.2 * Analyst M. Soroiu; ** Contamination. Institutul Geological României 3 CHLORITIZATION OF BIOTITES AND. IȚS BEARING ON K-AR AGES 135 in the Ruschița region, yet on a much smaller scale. On the lower line the samples of several bodies of the Ruschița alignment are plotted (13PR, 14PR. 32PR, 33PR, 34PR, 38PR). Sample 6PR from Ruschița is situated right between the two lines, so that it could eventually represent an independent phase of less importance. Sample 28PR. Fig. 2 — K-Ar diagrams for biotite concentrates of the Alpine igneous rocks (banatites) from the south-western part of the Poiana Rusca Massif. □ , intrusive bodies of the Ruschița alignment ; △ , intrusive body of Tincova ; dykes. should actually lie on the upper line. The reason why it does not fit in rests on the fact that the biotite concentrate contains a greater percentage of impurities, which influenced the K and Ar determinations negatively. The same explanation is valid for samples 37PR and 38PR, which belong to the Ruschița Group. A careful examination of the correlation between the K-contents of biotites and the calculated ages emphasizes the general tendency of increasing ages with decreasing K-contents. Such inverse relations are mentioned from several other places (e.g. Hopkins, Silberman, 1978), where they were attributed to a gain of extraneous argon by the rocks or minerals subiect to age determinations. In this view, the K-Ar diagrams of Figure 2 would be nothing but Harper isochrons. both show- ing small amounts of excess argon in the biotites under consideration. However, this can hardly be accepted. According to Harper (1970), excess argon in coeval rocks is constant, irrespective of their K-contents. In our case that would mean either that biotites had from the very beginning nearly the same K-contents as those actually determined, or that by potassium loss an equivalent loss of radiogenic argon occur- red. The first alternative can be ruled out, because the biotites in question are almost all partially chloritized. Their K-contents, generally Institutul Geological României 136 C. STR'UTINSKr et al. 4 less than 7% (Tab.), are good evidence in this respect (Wilson, 1972). The second alternative may be unacceptable, as well, for the reasons displayed further on. Discussion and Conclusions In case of the analysed biotites it has been proved, optically, as well as by X-ray diffraction, that the potassium decrease is generally reflecting their degree of chloritization. It should be mentioned that the biotite concentrates were obtained from generally unaltered rocks, and that chloritization, incipient but frequent, is due to weathering rather than to hydrothermal metasomatism, so that thermal events younger than the moment of consolidation may be excluded. Admitting now that the chloritization process is responsible for the increase of the K-Ar ages, there is seemingly no need any longer to resort to an extraneous source for the excess argon. According to Giletti (1971), the distribution of /,()Ar in a mineral is a function of the parțial pressure of this gas in the host rock. If, for any reason, during the history of the rock, the parțial pressure increases up to a certain degree, incorporation of 40Ar in the considered mineral would occur, and in this case “extraneous” excess argon would accumulate. Otherwise, different diffusion rates of potassium and argon during the chloritization process should be regarded as another mode of argon accumulation. Supposing the diffusion rate of potassium to be higher, there will be a relative enrichment of argon in the chloritized biotite, leading to the accumula- ion of what should be called “native” excess argon. A reason for the relative inerția of argon in the crystal lattice of biotite subject to chloritization would be expanding tendency of the lattice, as a con- sequence of potassium substitution by brucite layers (Troger, 1967). As a response, an increase of the parțial pressure of argon in the rock must be inferred, not as much as to permit incorporation of argon by the biotite lattice, but sufficient to lower the diffusion rate from within it. In practice this process seems to operate down to contents of about 4% potassium. Beyond this threshold a rapid expulsion of argon is noticed, indicated by the downward bending of the straight lines on the K-Ar diagrams (Figs. 2, 3, 4). This process is triggered most probably by the generation of fissures and cracks in the rock, at a moment when the resistance of mineral aggregates fails against the increasing pressures developed by the chloritization process. Such fissures, transecting the whole rock in from of a tiny veined network, have been observed microscopically in sample 33PR. The fissures are often filled with chlorite migrated from pseudomorphs after horn- blende and biotite. From our hypothesis it clearly evolves that the credibility of a K-Ar biotite age rises with the increase of the K-coritents, that is as chloritization approaches zero. Within a series of determinations on the same geological body, whose age, obtained on the purest biotite, should Ă Institutul Geologic al României XJGRZ 5 CHLORITIZATION OF BIOTITES AND ITS BEARING ON K-AR AGES 137 be the oldest, represent only an acceptable upper limit of the real age. Nevertheless, it should be stressed that such age interpretations apply only to rocks sufficiently young, or, at least, which prove that they did not undergo any other thermal event after the time of their formation. i0Ar m m i xlC*g I 2500 j 2000-i 1500' 1000 S00- 0 Fig. 3. — K-Ar diagram for biotite concentrates of the Central Srednogorie, Bulgaria (acc. to Boyadjiev and Lilov, 1981). Cal- cula ted ages (m.y.) in brackets. Ar 10 moie/g 91 7' 3- ■ 36-5'61.8: Fig. 4 — K-Ar diagram for biotite concentrates of the Utuado and San Lorenzo batholiths, Puerto Rico (acc. to Cox et al., 1977). Cal- culated ages (m.y.) in brackets. Similar interpretations as for the Poiana Ruscă Massif can be performed, for instance, for the Upper Cretaceous intrusions from Cen- tral Srednogorie-Bulgaria (Boyadjiev, Lilov, 1981) or Puerto Rico (Cox et al., 1977), or for the Tertiary ones from South Park-Breckenridge (USA) (Bryant et al., 1981). The k-Ar diagram for the Alpine intrusions nstitutul Geologic al României 13S C. STRUTINSKI et al. 6 from Central Srednogorie (Fig. 3) points out that they are coeval arid do not exceed 76 m.y. Similarly, as concerns the Utuado and San Lorenzo batholiths from Puerto Rico, the K-Ar diagram (Fig. 4) shows their cogenetic character and sets the upper limit of their age at 67,5 m.y. There is no evidence of two magmatic phases in case of the San Lorenzo Batholith, in spițe of K-Ar ages on hornblende con- centrates. It has to be mentioned that hornblende ages are subiect to greater errors than biotite ages, because of the very small K and Ar contents implicated, in connection with chloritization, biotitization or other alteration processes, which may produce serious and uncontrollable perturbations in the activity of hornblendes as “geological clocks”. Some othet- cases in which the credibility of hornblende ages is doubted are cited b.y Rice et al. (1982). As for the South Park-Breckenridge region (Bryant et al., 1981), the cliscrepancy between biotite ages of 44 to 50 m.y. and zircon, sphene and apatite ages of 35-42 m.y. may of course be due to excess argon, but not derived from Precambrian base- ment, as the.authors presume, but by internai accumulation of “native’’ argon, as emphasized in this paper. REFERENCES Eoyadjiev S. G., Lilov P. I. (1981) Potassium-argon Age Determinations of Alpine Intrusions in the Central Srednogorie. C. R. Acad. tmlg. Sci., 34/4, 549-551, Sofia. Bryant B., Marvin R. F., Naeser Ch. W., Mehnert H. H. (1981) Ages of Igneous Rocks in the South Park-Breckenridge Region, Colorado, and their Relation to the Tectonic History of the Front Range Uplift. U. S. Geol. Surv. Prof. Paper, 1199-C, 15-35. •Cox D. P., Marvin R. F., M’Gonigle J. W., Mclntyre D. H., Rogers C. L. (1977) Potassium-Argon Geochronology of some Metamorphic, Igneous, and Hydro- thermal Events in Puerto Rico and the Virgin Islands. J. Res. U.S. Geol. Surv., 5/6, 639-703. Giletti B. J. (1971) Discordant Isotopic Ages and Excess Argon in Bio'tites. Earth Planet. Sci. Lett., 10, 157-164. Harper, C. T. (1970) Graphical Solutions to the Problem of Radiogenic Argon-40 Loss from Metamorphic Minerals. Eclogae Geol. Helv., 63/1, 119-140. Hopkins D. M., Silberman M. L. (1978) Potassium-Argon Ages of Basement' Rocks from Saint George Island, Alaska. J. Res. U.S. Geol. Surv., 6/4, 435-438. Jankovie SI. (1977) Major Alpine Ore Deposits and Metallogenetic Units in the North-Eastern Mediterranean and Concepts of Plate Tectonics. In : Metallo- geny and Plate Tectonics in the NE Mediterranean. Univ. Belgrade, 105-171. Krăutner H. G., Krăutner FI. (1972) Report, archives of the “Banat” Geological Enterprise of Prospections and Exploration, Caransebeș. . Institutul Geologic al României 7 CHLORITIZATION OF BIOTITES AND 1TS BEARING ON K-AR AGES 139 Rice C. M., Lux D. R., Macintyre R. M. (1982) Timing of Mineralization and Related Intrusive Activity near Central City, Colorado. Econ. Geol., 77, 1655-1666. Strutinski C., Soroiu M., Catilina R., Paica M., Ocheană G. (in press) Potassium- Argon Geochronology of the Alpine Igneous Activity in the South-Western Part of the Poiana Ruscă Massif. Troger W. E. (1967) Optische Bestimmung der gesteinsbildenden Minerale. Teii 2. Textband. Schweizerbart. XI-|-822. Wilson M. R. (1972) Excess Radiogenic Argon in Metamorphic Amphiboles and Biotites from the Sulitjelma Region, Central Norwegian Caledonides. Earth Planet. Sci. Lett., 14, 403-412. Institutul Geological României Institutul Geological României Petrologie-Mineralogie TYPOMORPHISM OF SOME ORE MINERALS AND A PVT CLASSIFICATION OF CERTAIN ORE DEPOSITS BY GHEORGHE UDUBAȘA1 The following considerations include data on some Alpine ore deposits genetically related to Laramian and Neogene magmatites in Romania. The two calc-alkaline magmatic provinces show different dis- tribution areas (Fig. 1) and the main magmatic events are productive. Mineralizations are known both in volcanic and subvolcanic or hypabis- sal environments. In some parts of the distribution areas of the Neo- gene magmatites there occur together typical lava flows and subvolcanic bodies. Shallow depth hypabyssal or subvolcanic andesites rnay hardly be distinguished from the volcanic rocks of the same petrographic type. The subvolcanic mineralizations are characterized by a greater vertical extent as compared to those genetically related to the volcanic struc- tures. This is why an attempt was made to find out some typomorphic features of the mineralizations formed in two major settings : volcanic and subvolcanic or hypabyssal (Udubașa et al., in press). This papei’ represents a further research on this topics. Typomorphic Assemblages of Oxide Minerals in Igneous Rocks This discussion includes mainly igneous rocks of intermediate composition. In the study areas the rocks exhibit a nearly continuous variation of texture, from holocrystalline to porphyritic (with glassy matrix) rocks. The accessory opaque minerals are magnetite, ilmenite, maghernițe, sphene and hematite, occurring in nearly fresh or slightly transformed rocks. Rutile becomes important as the alteration proceeds (Udubașa, 1982). Pseudobrookite appears only in highly oxidized vol- canics. The gradual oxidation of the primary oxide minerals in igneous rocks is largely 'described by Haggerty (1976). Magnetite (mgt) is more homogeneous in volcanic rocks (especially in lava flows) but sandwich and trellis type ilmenite (Hm) lamellae 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 București 32. Romania. Institutul Geological României 142 G. UDUBAȘA 2 Fig. 1 — Distribution areas of Laramian (a) and Neogene (b) magmatites in Romania. AM, Apuseni Mountains, EC, East Carpathians, SC, South Carpathians, SZ, subvolcanic zone of the EC Neogene volcanic chain. Subvolcanic and hypabyssal rock areas and the discussed ore deposits : RS, Rotunda-Strîmbu, Ți, Țibleș, To, Toroiaga, Institutul Geological României 3 TYPOMORPHISM OF SOME ORE MINE'RALS 143 or separate grains are not rare. In such rocks it is the maghernițe (mgh) which seems to be a very frequent and typical alteration product of the mgt in nearly fresh or slightly altered rocks. In most cases mgh forms coronas around mgt grains or irregular veinlets along the joints ; it may be sometimes overlooked if no oii immersion is used. More complex features shows the mgt richer in Ti : nearly concentric hands of varying colour shades (from blue to grey) completely replace the mpt grains (Fig. 2, II b and c). Maghernițe has been often described in volcanic rocks (Katsura, Kushiro, 1961 ; Buddington, Lindsley, 1964 ; Ramdohr, 1975 ; Dankers, 1978 ; Freer, O’Reilly, 1980 etc.). However, its apperance in some intrusive rocks is also mentioned (Davidson, Wyllie, 1968 ; Czamanske, Mihalik, 1972 ; Gasparini, Naldrett, 1972 etc.). Magnetite grains in subvolcanic or hypabyssal rocks are more complicatedly featured. The sandwich and trellis type ilm lamellae are abundantly developed. In addition, very fine, ulvospinel (usp)-derived Um lamellae may be observed in places. The most typical feature of such (nearly fresh or slightly autometamorphicaly altered) rocks is the development of the secondary sphene. The sphenitization is also occurring on the fine, asp-derived ilm lamellae and the replacement is sometimes zonally evoluted (Fig. 2, I a). The secondary sphene has not been observed in samples of lava flows. In turn, mgt in some hypabys- sal rocks may contam mgh as regular spots obeying the crystallographic planes in mgt. Elsewhere sphene was often observed in intrusive rocks (Davidson, Wyllie, 1968 ; Czamanske, Mihalik, 1972 ; Gasparini, Naldrett, 1972 ; Tsusue, Ishihara, 1975, etc.) ; it has been very rarely mentioned to occur in some basalts (Basta, Shaalan, 1974). Breccia Formation The best developed mineralized breecias are known in some por- phyry copper (especialiy of Neogene age) and in some base metal ore deposits (Laramian and Neogene). At Rodna the breccia formation re- presents an intramineralizaion proeess and it seems to have appeared after the main ore phase was formed. The breccia is andesitic in cha- racter and bears both fragments of metamorphic limestones (partly re- placed by ore) as well as fragments of ores belonging to the first phase and metamorphosed ores of Blazna-Gușet type. The Baia de Arieș ore deposit also exhibits andesitic breccia with metamorphic limestones, whereas the breccia occurring at Bocșa-Săcărîmb is nearly purely andesitic in lithology ; it developed in an older lava flow situated some tens of metres over the hypabyssal body of quartz microdiorites. The subvolcanic body at Coranda-Hondol is enveloped at the top by brec- ciated Cretaceous black shales and sandstones. A similar constitution has the mineralized breccia at Rotunda-Strîmbu. At Rușchița the brec- cia seems to represent a mixed formation of both eruptive and tectonic origin. Less developed breecias are present at Julești-Valea Fagului. No breccia at all is known at Toroiaga (Bor&ș -et1 al.1, 1982). Foi' more -.details see Udubașa et al. (in press). , , Institutul Geological României IGR Fig- 2 — Types of oxide mineral intergrowths in subvolcanic (I) and volcanic (n> rocks. Institutul Geological României 5 TYPOMORPHISM OF SOME ORE MINERALS 145 Ore Mineral Assemblages in Ores The ore deposits under discussion have a lead-zinc character ; copper-rich ores or copper enrichment show those at Toroiaga, Julești- Valea Fagului and Țibleș (southern part). Sphalerite and galena together with pyrite (and chalcopyrite) are the dominant ore minerals. There occur aJso some sulphosalts (among them bournonite predominates) as. late differentiates or late phases. Some porphyry copper systems are accompanied by base metal ore veins as late formations ; the ores in such veins always contain iron poor sphalerite, e.g. Bolcana-Troița, Metaliferi Mts ; South Țibleș etc. Pyrrhotite (po) as separate aggregates is present only at Țibleș. Rodna and Toroiaga ; commonly it occurs within the multiphase inclu- sions in sphalerite (sph), too. Pyrite (py) is always present but it is less frequently occurring in the copper-rich, bornite bearing ores at Julești-Valea Fagului as well as in the nearly pure lead-zinc ores from Rușchița. The same is true for arsenopyrite. Galena is an ubiquitous mineral and bears some sulphosalts at Rodna, Toroiaga, Coranda-Hondol and Bocșa-Săcărîmb. Chalcopyrite is abundant at Toroiaga (as an early mineral associated with po and py) and at Julești-Valea Fagului (as- sociated with bornite). At Bocșa-Săcărîmb there were observed some chalcopyrite crystals in vugs. Sphalerite exhibits the most complicated features. It contains vary- ing iron contents (from 1 up to 15 wt.-% Fe), and, accordingly, inclu- sions of different compositions. The iron rich (10-15wt.-% Fe) sph bears multiphase inclusions containing chalcopyrite (cp), pyrrhotite (po), chalcopyrrhotite or the intermediate solid solution (iss)- of the Cu-Fe-S system, cubanite (cb) and mackinawite (mck). These minor phases are differently textured and are of varying dimensions (Fig. 3). The com- plexity of inclusions is decreasing as the iron content in sph decreases : the sph with 3-6 wt.-% Fe contains only cp (Baia de Arieș ; the ores contain also alabandite) or cp-j-tss (Bocșa-Săcărîmb) and the iron poor 1 a, a grain of mgt with usp-derived fine ilm lamellae, zonally transformed into sphene; granodiorite, Țibleș Neogene igneous complex ; I b, sandwich type ilm lamellae in mgt partly altered to sphene ; lamprophyre, dyke swarm of Liassic age, East Făgăraș Mts ; I c, trellis type ilm lamellae ; the mgt “islands” are sphenitized ; microdiorite, Rotunda-Stnîmbu Baia Mare area ; I d, sandwich type ilm lamellae completely transformed into sphene ; monzodiorite, Țibleș igneous complex ; II a, mgh developed in a mgt grain with fine ilm lamellae ; Neogene pyroxene andesite, Baia Mare Area, N Romania ; II b, banded mgh-timgh develop- ed on a homogeneous mgt grain ; Neogene pyroxene andesite. Baia Mare area ; II c, “scaly” hematite formed on mgt via mgh with preservation of ilm lamellae ; lava flow of Neogene quartz andesite, Bocșa-Săcărîmb ; II d, timgh formed at the borders of a ilm grain ; Neogene pyroxene andesite, Baia Mare area. 1, mag- netite ; 2, ilmenite ; 3, sphene ; 3a, sphene (in I a only) ; 4, maghernițe ; 5, titano- maghemite ; 6, hematite. Institutul Geological României 1-16 G. UDUBAȘA 6 sph at Coranda-Hondol, Rușchița (with 1-2.5 wt.-% Fe) bears only cp and occasionally mck. Two-phase inclusions consisting of cp+bn were observed in the sph from the Julești-Valea Fagului ores. Fig. 3. — Types of inclusions in sphalerites : A-D, iron rich sph (10-15 wt.-% Fe) ; E, sph with 6 wt.-% Fe ; F-G, iron poor sph (1.0-2.7 wt.-% Fe). The greater inclusions in B and C reflect țhe derivation of the coexisting minerals from the high T iss ; the po is grown in a phase resembling cp, not distinguishable from the cp of the laths (B) ; coexisting cb and mck developed on a sol-sol matrix with lanceolate cp laths suggesting a paramorphic transformation of a high Ț phase. The smaller inclusions contain only frozen assemblages, in which mck does not occur togețher with iss (cpo) as cb sometimes does (in B). A, Rodna ; B, Toroiaga ; C, Țibleș ; D, Rotunda-Strîmbu ; E, Bocșa-Săcărîmb ; F, Coranda-Hondol ; G, Julești-Valea Fagului. 1, chalcopyrite (cp); 2, “chalcd- pyrrhotite” or iss; 3, cubanite (cb) ; 4, pyrrhotite (po); 5, mackinawite (mck)•; 6, bornite (bn). Institutul Geological României 7 TYPOMORPHISM OF SOME ORE MINERALS 147 Some Typochemical Features In order to distinguish the volcanic from the subvolcanic mineral assemblages, the diagrammatic representation of some minor elements contained by the main sulphides was used (Udubașa et al., in press). The most interesting diagram is given in Figure 4. The subvolcanic sph concentrates into a relatively well delimited field, no matter that the- Cu Fig. 4. — Cu-Mn-Cd diagram for sphalerite. 1, subvolcanic sphalerites ; 2, sphalerite from other ore deposits (mainly of voi-, canic setting) ; 3, field of subvolcanic sphalerites. sphalerite is iron rich or iron poor. However, the iron rich sph plots mostly towards the Mn corner whereas the iron poor sph plots towards the Cd corner. The Mn : Cd ratio, is thus fairly constant, reflecting a typical feature of the subvolcanic sph, i.e. an “equilibrium concentration” of these elements. The Ag-Bi-Sb diagram does not discriminate the volcanic and sub- volcanic galenas. Most of the plottings concentrate at corresponding Institutul Geological României 148 G. UDUBAȘA 8 values of the compounds AgBiS2 and AgSbSo (Fig. 5). However, the field of plottings is much larger, showing the extent of solubility of Ag, Bi and Sb in natural galenas. The space towards the Bi-Sb edge is practically free (less than 4% of total plottings) suggesting a very limited solubility of the BiSb pair, as inferred from the experimental Fig. 5. — Ag-Sb-Bi diagram for galena : A, the evolution trend from Laramian (4) to Neogene (5) ; B, the behaviour of galenas from low T to high T assemblages (arrows) in Laramian and Neogene ore deposits. 1, subvolcanic galenas ; 2, average values of subvolcanic galenas ; 3, other galenas (mainly of volcanic setting) ; 4, (in A) field of Laramian galenas ; 5, field of Neogene galenas. data of Amcoff (1976) too. The Laramian galenas concentrate towards the AgBi edge whereas the Neogene galenas towards the AgSb edge ; however, galena from high-T assemblages of Neogene age tends to migrate to higher Bi contents too. The trend is not only temperature dependent but indicates also that the galena seems to be geochemically much more linked to the age and regional characteristics of the ore deposits than the sph is. Institutul Geological României TYPOMORPHISM OF SOME ORE MINERALS Discussion The ore deposits under discussion are genetically related to Lara- mian and Neogene subvolcanic and hypabyssal rocks of andesitic com- position Consolidated at various depths. In such cases one can admit that the total volatile pressure (Pv) of the postmagmatic Systems was roughly equilibrated by the lithostatic pressure (P i). The primary oxide minerals in the related igneous rocks indicate for all cases a relatively low fot. The assemblage mpt+sphene seems to be a typomorphic feature of the non-erupted rocks (generally slight- ly altered) as against the typical lava flows constantly exhibiting the assemblage mgt-\-(ti)mgh. This fact points to a low Pco2 as shown by the sphene stability diagram of Schuiling and Vink (1967), within the consolidating and decompressing magmatic systems. In some cases, e.g. the Toroiaga igneous complex, mgh has been observed forming regular spots in the inner parts of the mgt grains (high T mgh 2) ; sphene is, howver, rather frequently occurring too. The greater fo2 in this case correlates with the high T massive deposition of cp (bearing sph stars) prior to the sph and gn deposition, The “excess” copper in these ores might have originated also in the remobilisation (at least partly) of the pre-existing metamorphosed ores of Lower Paleozoic age intruded by the Neogene andesitic rocks and cut by the hydrothermal vein ores. If the sph geobarometer (Scott, 1973 ; Scott, Barnes, 1971 ; Lusk, Ford, 1978 ; Hutcheon, 1980 ; Shimizu. Shimazaki, 1981 etc.) is applied to such ore deposits, it is interesting to note an inverse relationship between T and Pv. High T assemblages containing po, apy, iron-rich sph with multiple inclusions of cp, iss, po, cb and mck seem to associate with low Pv postmagmatic environment, i.e. ores at Toroiaga, Țibleș and Rodna (if skarn minerals are present then the ores are subsequently formed). Low T assemblages with iron poor sph bearing inclusions of cpimck may further be ascribed to high Pv conditions, i.e. ores at Rușchița and Coranda-Hondol ; such ores associate with large scale breccia formation suggesting high volatile pressure in the postmagmatic fluids. The other deposits containing sph with moderate iron content, i.e. Baia de Arieș and Bocșa-Săcărîmb, may be regarded as formed at intermediate T and Pv; they show also mineralized breccia. TABLE 1 Iron content in sphalerite and related mineral assemblages as funclion of T and fs2 Mukaiyama, Izawa 1971) This study Mole %FeS Assemblages Mole % FcS Assemblages* >23 14-23 9-14 0-12 < 1 cp, cb, hpo high T 1< cp. hpo •1 cp, py, mpo cp, py cp, bn, py low T hi nv fs2 14-25 10-12 . 1.5-2.7 Sh f52 1-2 cp, iss, cb, po, mck cp, po, iss cp, mck cp, bn’ * as inclusions in sph; all assemblages contain py too. ' L Institutui Geological României 150 G. UDUBAȘA As Mukaiyama and Izawa (1971) showed for some Japanese ore deposits the sph-bearing assemblages are temperature dependant (Tab. 1). If such a T arrangement is correlated with the Pv regime of mineral deposition, as shown by the iron content in sph and by the presence of breccia in certain ore deposits, one can obtain a classification of mineral assemblages in terms of T and Pv (Tab. 2). Such a treatment TABLE 2 The PVT grouping of the ore deposits prescnled in this study Pv, T estimated Ore deposits Main characteristics High T, low Pv Intermediate T and Pv Low T, high Pv Toroiaga Rodna Țibleș Rotunda-Strimbu Bocșa-Săcărimb Baia de Arieș Coranda-Hondol Rușchița Țibleș (south) Julești-Valeâ Fagului Bolcana-Troi(a* No breccia formation 17 — 25 mole % FeS in sph Multiphase inclusions in sph (see Table 1) Sphalerite has a nearly constant Mn: Cd ratio, but Mn is statistically slightly enriched Galena is slightly enriched in BiAg Abundant breccia formation 5 — 10 mole % FeS in sph Two-phase inclusions in sph (cp, iss) Abundant breccia formation 1—4 .5 mole % FeS in sph Inclusions in sph consist of cp, mck Sphalerite has a nearly constant Mn: Cd ratio, but Cd is statistically slightly enriched Galena is slightly enriched in SbAg * Pb-Zn ore veins cutting the porphyry coppcr System. of facts allows to attenuate the apparent discrepancy between the experimental data regarding the relation of the iron content in sph and its T of formation. This is not an attempt to revive the sph geo- thermometer. but to find out an explanation for the iron rich sph occurring in high T and low P assemblages. The model presented above can be applied only to subvolcanic and hypabyssal environments, which are complementary assured by the typomorphic assemblage mpt+sphene in the related igneous rocks (as against the stabilized assemblage mgt-\-(ti)mgh, currently occurring in lava flows). 2 epo (chalcopyrrhotite) or iss as used in this paper is a phase having an intermediate colour between po and cp ; it is lighter than the cb, mostly isotropic, but sometimes becomes slightly anisotropic (gradual transformation into cb ?) es- pecially when mck is appearing (see Fig. 3 B). The phase is somewhat similar to the talnakhite but it does not tarnish and the optical properties fit well with those of epo described by Ramdohr (1975). However, it is clear that the iron rich sph contains inclusions of a high T solid solution which decomposes step by step by decreasing T, giving cp-\-cb, cp+po or cp+cb+mck (metastable assemblage), or the quenching products — the iss itself — occurring in relatively quickly cooled ores. If TYPOMORPHISM OF SOME ORE MINERALS 15 f REFERENCES Amcoff O. (1976) The Solubility of Silvei-, and Antimony in Galena. N. Jb. Miner. Mh. 6, 247-261, Stuttgart. Basta E. Z., Shaalan M. M. B. (1974) Distribution of Opaque Minerals in the Tertiary Volcanic Rocks of Yaman and Aden. IV. Jb. Miner., Abh. 121, 25-102, Stuttgart. Eorcoș M.. Andăr P., Andăr A., Berza T. (1982) Gsochimia mineralizațiilor poli- metalice din cîmpul minier Toroiaga (Baia Borșa, Munții Maramureșului). D. S. Inst. geol. geofiz.,. LXVII/2, 55-82, București. Buddington A. F., Lindsley D. H. (1964) Iron-titanium Oxide. Minerals and Syn- thetic Equivalents. J. Petrol., 5, 310-357, London. Czamanske G. K., Mihalik (1972) Oxidation During Magmatic Differentiation, Finn- marka Complex, Oslo Area, Norway : Part 1, The Opaque Oxides. J. Petrol-, 13, 439-509, London. Dankers P. H. M. (1978) Magnetic Properties of Dispersed Natural Iron Oxides of Known Grain Size. Diss. State Univ. Utrecht, XIII-[-142 p., Utrecht. Davidson A., Wyllie P. J. (1968) Opaque Minerals of Some Diabase-Granophyre Associations in Pennsy.lvania. Econ. Geol., 63, 950-960, Lancaster. Freer R., O’Reilly W. (1980) The Diffusion of Fe2+ lons in Spinels with Relevance to the Process of Maghemitization. Mineral. Mag,, 43/331, 889-899, London. Haggerty S. E. (1976) Opaque Mineral Oxides in Terrestrial Igneous Rocks. In : D. Rumble III (ed.) Oxide minerals. Miner. Soc. America, Short Course Notes, voi. 3, Hg 101-Hg 300, Blacksburg, Va. Hutcheon J. (1980) Calculated Phase Relations for Pyrite-Pyrrhotite-Sphalerite: Correction. Amer. Mineral., 65, 1063-1064, Washington. Katsura T., Kushiro I. (1961) Titanomaghemite in Igneous Rocks. Amer. Mineral., 46, 135-145, Menasha. Lusk J., Ford C. E. (1978) Experimental Extension of the Sphalerite Geobaro- meter to 10 kbar. Amer. Mineral., 63, 516-519, Washington. Mukaiyama H., Izawa E. (1971) Assemblages of Sulfide Minerals in Hydrothermal Deposits : The System Cu-Fe-Zn-S. Mineral. Soc. Japan, Spec. Pap. 1 (Proc. IMA-IAGOD Meetings ’70, IMA Voi.), 271-272, Tokio. Prevot M., Remond G., Caye R- (1968) Etude de la transformation d’une titano- magnetite en titanomaghemite dans une roche volcanique. Bull. Soc. fr. min. crist., 91, 65-74, Paris. Ramdohr P. (1975) Die Erzmineraiien und ihre Verwachsungen. Acad. Verlag. 1277 p., Berlin. Schuiling R. D., Vink B. W. (1967) Stability Relations of Some Titanium-minerals (Sphene, Perovskite, Rutile, Anatase). Geoch. Cosmoch. Acta, 31, 2399-2411, Belfast. Institutul Geological României 152 G. UDUBAȘA S2 Scott S. D. (1973) Experimental Calibration of the Sphalerite Geobarometer. Econ. Geol., 68, 466-474, Lancaster. — Barnes H. L. (1971) Sphalerite Geothermometry and Geobarometry. Econ. Geol. 66, 653-669, Lancaster. Shimizu M., Shimazaki H. (1981) Application of the Sphalerite Geobarometer to Some Skarn-type Ore Deposits. Mineral. Deposita 16, 45-50, Berlin. Tsusue A., Ishihara S. (1975) “Residual” Iron Sand Deposits of Southwest Japan. Econ. Geol. 70, 706-716, Lancaster. Udubașa G. (1982) Rutile of Postmagmatic Mineral Formation. In : G. C. Amstutz et al. (eds.) Ore Genesis — the State of the Art. 784-793, Springer, Berlin- Heidelberg-New York. Institutul Geological României Gisements ORE TEXTURE AND STRUCTURE OF SULPHIDE-IRON OXIDES OF THE PRECAMBRIAN ALTlN TEPE DEPOSIT, DOBROGEA (ROMANIA) BY ION BERBELEAC *, AVRAM ȘTEFAN 1 Introduction Among the great diversity of stratiform metamorphosed hydro- thermal-sedimentary ores in metamorphic schists the sulphide-iron oxide Altîn Tepe deposit represents a particular type. The peculiarities of ore textures and structures observed in polished hand specimens and polished sections help us to solve some problems regarding especially the origin and metamorphic processes of ore. Geological Setting The geological characteristics of the ore deposit are given in a number of works (Codarcea, Petrulian, 1948 ; Gurău, 1970 ; Mureșan, 1969. 1972 ; lanovici et al., 1971 ; Berbeleac et al., 1983). The investigated deposit is situated in the Upper Precambrian metamorphic schists (1600-850 m.y.) which form a regionally extended belt trending north-westwards. Several geological units are parallel to the belt : northwards there are unmetamorphosed Paleozoic (Carapelit Formation — Permo-Carboniferous) and Mesozoic rocks (Triassic-Upper Cretaceous) ; southwards lies the greenschist series of Upper Precam- brian age (800-575 m.y.) which underwent a low-grade metamorphism. while north-eastwards there occur Triassic rhyolitic rocks. The rocks of the Altîn Tepe Series represent a normal monoclinal flank with north-western strike (N 35-65° W). The B axis dips by 30-45° towards the south-east. The greenschist series overthrusts the Altîn Tepe Series and a great number of faults are present. According to the age the Altîn Tepe Series may be subdivided in two lithostratigraphic units : 1) the lower unit (Fig. 1 a), over 2 500 m thick, which includes high grade metamorphosed sediments 1 Institute of Geology and Geophysics. str. Caransebeș 1, 78344 Bucharest. Institutul Geological României 154 I. BERBELEAC, A. ȘTEFAN 14 (gneisses, amphibolite, quartz biotite, etc.), plutonic (gabbro, diorite) and volcanic (tuffs, basaltic lavas, etc.) rocks and 2) upper unit, probably 150-200 m thick, also high grade metamorphosed but strongiy retro- morphosed, consisting of quartz-feldspar-chlorite schists (80-100 m, Fig. 1, b, c) interlayered with quartz-muscovite-biotite+garnet schists, quartz-chlorite-sericite schists and amphibolite schists in the lower part. Fig. 1 — Stratigrapbic column of the Altîn Tepe Series (a-c) and the geometry of ore lenses at levei —750 m(d). a, Baspunar-AItîn Tepe zone ; b, upper unit at levei —750 m in the area of lenses nos. 1 and 2 (o). 1, a, gneiss, micaschist, biotite quartzite, etc.; b, amphibolite; 2, upper unit t .3, Greenschist Series ; 4. a, chlorite-quartz schist ; b, chlorite-feldspar-quartz schist; 5, a, massive ore lenses ; b, disseminated ore ; 6, disseminated pyrite- ore ; 7, disseminated sulphide ore ; 8, sulphide-iron oxide ore ; 9, fault. L I, L II, lense number.- and sericite-chlorite quartz schists and chlorite-albite schists with minor intercalations of quartzite, quartz-feldspathic schists and amphibole schists in the upper part (70-100 m, Fig. 1, b, c). The ore deposit lies in the upper part of the upper unit. The presence of staurolite and gârneț in the rocks of the Altîn Tepe Series points to the metamorphic amphibolite facies. Ore Deposit At present the mining works reach the levei of -750 m (580 m below sea levei) and a recent borehole has reached the ore at the depth of 530 m below this levei. It means that on the plane of plunge (30-45° SE) the ore deposit was controlled along more than 3 km. 15 ORE TEXTURE AND STRUCTURE ALTÎN TEPE DEPOSIT 155 Two types of mineralization occur in the Altîn Tepe deposit : 1) sulphide-iron oxides massive ore lenses, obviously related to the chlorite-sericite quartz schists, quartz-aibite-epidote+barite schists, quartz-sericite schists and other types of rocks and 2) disseminated pyrite-chalcopyrite+sphalerite, galena ore, which lies both in quartz- sericite schists and chlorite-quartz+albite schists from inside massive ore lenses or from a halo in their hanging wall and footwall (Fig. Id). The massive ore forms four small lenses (nos. 1, 2, 3, 4) in the upper levels of the deposit and three small lenses (nos. 1, 2, 3) in the lower part of the deposit. The dimensions of the massive ore lenses are small and on the strike the length ranges between 30-80 m, while the thickness varies between 2-18 m. Ore bodies form either alternations of banded highlv impregnated to compact pyrite-chalcopyrite+sphalerite, galena with magnetite+sul- phides, hematite or with quartzitic, sericitic or chloritic albite schists which are poorly mineralized. The dissemination bodies (IA. 1B, 2A, 2B, 3A, 3B) are related especially to quartz-rich serici te schists and appear at the exterior of the massive ore or at different levels of the upper part associated w’ith chlorite-quartz+albite schist and amphibolite schist. This type of ore is larger than the massive ore and consists mainly of pyrite, minor chalcopyrite. very small amounts of sphalerite and galena and accident- ally magnetite. The authors think that the original ore deposit has a hydro- thermal-sedimentary origin, being later modified by prograde and retro- grade metamorphism. Ore Texture and Structure Many prominent features of the Altîn Tepe ore are. in the authors’ opinion, compatible with the pro- and retrograde metamor- phism. These features suggest many similarities to the ore bodies described by Vokes (1969), Suffel et al. (1971) and Lawrence (1973). Some of these characteristics of ore metamorphism are generally commented upon by other authors (Stanton, 1972 ; Shadlum. 1982). Before describ- ing the ore polymetamorphism from Altîn Tepe, we remind and point out the fact that the ore bodies are situated within a retrogressive sequence of rocks. Prograde Ore Banded texture. The most striking primary textural feature of the ore is usually the fine compositional banding ranging from 0.1 to 10-15 cm in thickness (Fig. 2 b). However, many compositional bandings between 15-150 cm in thickness are known in massive ore lenses, while others, ranging between 3-20 cm in thickness are found in dis- seminated ore (Fig. 2 a). The layering is structurally concordant with the ore host-rock contacte and with the bedding primary origin. The most typical peculiarity of textures is the presence of numerous alter- nating rhythms or microrhythms with the same or different structures Institutul Geological României 156 I. BERBELEAC, A. ȘTEFAN 16 BO 00 o £ ££ jHfU Institutul Geologic al României IGR/ 17 ORE TEXTURE AND STRUCTURE—AiTlN TEPE DEPOSIT 157 U U U \lGR/ Institutul Geological României 158 I. BERBELEAC, A. ȘTEFAN 18 and mineralogica! composition. The layered sulphide and iron oxide bands in massive ore lenses and sulphide bands in disseminated ore, are interlayered with schist bands (Fig. 2 c). In the almandine-amphibolite facies the competent minerals, such as quartz, pyrite and magnetite from banded massive ore, are frequently stretched, become discontinuous and form boudins. Sometimes even schistose rock fragments or muscovite, sericite and chlorite are de- tached, contorted and rounded up by tectonic rolling (Fig. 3 a, b). Even thin bands of quartz-pyrite and quartz-magnetite+barite ore are laminated or completely detached. In connection with this, pyrite and magnetite “bulls”, which are rounded or nearly rounded, are present. In our opinion this type of texture rnay be assumed as a retrogressive texture. The insignificant presence of these textures, typically composed of “mixed” ore, in lense no. 2, rnay be due to the decrease of the retromorphism degree towards the lower parts of the upper unit — se- quence of the Altîn Tepe Series. In prograde ores the average structure ore is medium- and coarse- grained (Fig. 3 c). It is not uncommon to see pyrite and magnetite crystals as much as 2-3 mm in size. Chalcopyrite and sphalerite are minor constituents, being comparatively medium-grained. It is important to underline that in the above-mentioned structure persist all the main assemblages : pyrite-quartz ; magnetite (hematite)-quartz-barite and pyrite-chalcopyrite-sphalerite (galena)-quartz. Some heterogeneous struc- tures which have been observed in the ore rnay be due to the variation in the inițial mineralogicail-chemical compositions and metamorphic processes. For instance the poikiloblastic structures for magnetite, sulphide, quartz or any silicate are present (Fig. 4). Resorption, re- crystallization and the structures involving co-recrystallization of sul- phides and gangue minerals have been noticed. The co-recrystallization of chalcopyrite with quartz, muscovite. marked by smoothly curved or curvilinear interphase boundaries are sometimes remarkable. Also, chalcopyrite shows broad twin lamellae (Fig. 9). This mineral as well as sphalerite serve frequently as cement for magnetite and pyrite ag- gregates (Fig. 5). Retrograde Ore Mesoscopic characteristics of the ore from the retrograde zones are best seen on polished slabs under a binocular microscope. The ore is practically brecciated and intersected by numerous stress zones ; the fissures are filled by plastic injections or “filter pressed” chalcopyrite. Like the retrograde ore from the Broken Hill sulphide ore bodies (Lawrence, 1973) the fragments of wall rocks and prograde ore are prominent in the retrograde ore of Altîn Tepe. Breccia texture. A very common and characteristic type of ore from lenses 1 and 3 are breccia textures. These textures consist of two principal types : 1) “bull texture" formed by medium and coarse pyrite, magnetite, quartz and silicate fragments, rather closely paeked in a Institutul Geological României 19 ORE TEXTURE AND STRUCTURE—ADT1N TEPE DEPOSIT 159 matrix of chalcopyrite, sphalerite and galena (Fig. 3 b) and 2) breccia texture, which consists of very fine-grained minerals (Fig. 3 a, Fig. 6). The latter type appears locally, generally along the longitudinal faults or shearing zones (Fig.-10). The breccia textures represent especially more than 80% from the total volume of the lenses 1 and 3. The main features of these textures are the following : 1) the banded aspect which consists of rhythms of mixed ore composed of pyrite and magnetite “bulls” and fragments of rocks or other minerals in a matrix of sulphides, quartz and barite ; 2) the disappearance in general of the bed primary origin of ore, initially marked by well-defined bands of uniform mineralogical- chemical compositions and the appearance of local enrichments ; 3) the presence of intrusive deformations which are responsible for cataclastic ore and slipping microfolds (Fig. 6) and 4) the existence of a great homogeneity of the ore structures. The breccia texture, which consists of fine-grained ore, shows a slight orientation and bandings (Fig. 3 b). This ore has a remarkable number of inclusions, which differ in composition : quartz-magnetite+ +barite ; quartz-sericite-chlorite schists, milky quartz, relict pyrite and magnetite porphyroblasts. The inclusions vary from large blocks, es- pecially of milky quartz and quartz-sericite-chlorite schists ; some of these are severely folded and crenulated, others are rounded or angular in shape (quartz) (Fig. 7). Chalcopyrite+galena and rarely sphalerite show injections, especially into quartz-magnetite-|-barite ore and milky quartz. The sources of the ore fragments are the quartz veins from the country rocks or from massive ore and the barren rocks. The breccia cement of fine-grained ore is very rich in chalcopyrite and sphalerite. Although galena is a minor constituent, here it shows the highest content. We have previously mentioned the relict prograde texture and structure of the ore within the lenses 1 and 3. (Fig. 10 a, c). Between ihe relics of prograde ore and retrograde ore there is a transition zone marked by homogeneous. pyritic or iron-oxide ore, but with breccia texture. A common and characteristic feature of this ore is the existence of the slight signs of flowage and particularly of shearing. As a result of retrograde metamorphism the inițial structure of the ore was partly subsequently modified. The principal modifications of massive ore consist in : 1) the decrease of the grain-sizes (0.1-0.5 mm) ; 2) the substructures of chalco- pyrite and galena ; 3) complex superimposed twinning of magnetite and chalcopyrite (Figs. 8, 9) ; 4) the presence of chalcopyrite inclusions (exsolution) within sphalerite ; 5) the fine dispersed sulphides in gangue minerals : 6) the increase of the degree of martitization in magnetite and 7) the appearance of small euhedral pyrite crystals in massive breccia ore (0.1-0.5 mm). As regards the disseminated ore we point out that the pyrite aggregates or isolated grains have been subject to fracturing and crush- ing. Texture and structure peculiarities of these aggregates show quite distinctly their formation in connection with mylonitization processes. . -A Institutui Geological României \igrX 160 I. BERBELEAC, A. ȘTEFAN 20 Fig. 10 — Details of the ore lenses. 1, chlorite-quartz + feldspar schist ; 2, chlorite-quartz schist and sericite-quartz- schist ; 3, amphibolite and chlorite-quartz feldspar-epidote schist ; 4, quartz blocks : 5, prograde ore with relics of retrograde ore ; 6, retrograde ore ; 7, magnetite ore : L 1, 2, 3 — lense number ; mining levels —650 and —750 m. Institutul Geologic a României 21 ORE TEXTURE AND STRUCTURE-ALTlN TEPE DEPOSIT 161 In some cases the growth of pyrite has been disturbed, showing elongat- ed shapes or “en echelon” distribution. The pyrite and sphalerite deposition, like in massive ore, was obviously accompanied by brecciation and partly corroded by abrasive Solutions of later pyrite, quartz and barite. This pyrite was immediately redeposited as fine skeletal grains. Conclusions 1. The Altîn Tepe ore deposit lies within a retromorphic sequence in the neighbourhood of an important overthrust and is composed of predominantly quartz-sericite-chlorite mylonitized schists. Initially the rocks of this sequence of the upper unit of the Altîn Tepe Series have been metamorphosed in amphibolite facies. 2. Both types of massive and disseminated ore preserve the peculiarities of pro- and retrograde metamorphism. The effects of the retrograde metamorphism are generally more visible in the massive ore of lenses 1 and 3 and the surrounding disseminated ore. 3. The most essential texture and structure ore peculiarities are the following : a) the rhythmically stratified textures, with fine to coarse interstratification of sulphide (especially pyrite) with layers of quartz- magnetite+barite and quartz-sericite-chlorite schists ; b) they preserve in general the inițial limits between the ore layers and schists and the ore homogeneity and c) the presence of the ore medium-coarse grano- blastic structure. 4. The typicai peculiarities of retrograde ore consist in : a) the breccia texture with slight aspect of banded texture, which shows two principal aspects : the "bull texture” which consists more often of rounded grains of pyrite, magnetite and quartz in a matrix of plastic sulphide and gangue minerals ; b) the breccia texture with very fine- grained sulphide in cement and different fragments of quartz is asso- ciated with faults and shear zones and c) the fine-grained granoblastic structure and the superimposed twinning of the magnetite, chalcopyrite and sphalerite. 5. The textural and structural features of the Altîn Tepe ore de- posir show many similarities to other ores from Broken Hill, Australia (Lawrence, 1973), Norway (Vokes, 1969), Kholodninskoe, U.S.S.R. (Shad- lum, 1982) etc. REFERENCES Berbeleac I., Ștefan A., Andăr A., Zămîrcă A., David M.. Dumitru E., Nițu (in press) Mineralogy, Textures and Geochemistry of Altîn Tepe Massive^" Sulphide-Iron Oxides Deposit. Central Dobrogea. D. S. Inst. geol. geofiz., București. Codarcea Al., Petrulian N. (1948) Report, archives of the Geological Institute, Bucharest. H - e. 667 162 I. BERBELEAC, A. ȘTEFAN 22 Gurău A. (1970) Structura în budine eșalonate a zăcămîntului Altîn Tepe-Movila Săpată. D. S. Inst. geol., LVI/5, București. lanovici V., Dumitriu Al., Andăr P. (1971) Considerații chimico-statistice asupra genezei mineralizației de la Altîn Tepe. D. S. Inst. geol., LVIII/2, București. Lawrence L. J. (1973) Polymetamorphism of the Sulphide Ore of Broken Hill, NSW, Australia, Mineral. Deposita, 8, p. 211-236. Mureșan M. (1969) Studii asupra zăcămîntului de pirită cu magnetit de la Altîn Tepe (Dobrogea centrală). I. încadrarea genetică a mineralizației. D. S. Com. Geol., LIV, 2 (1966-1967), București. — (1972) Studii asupra zăcămîntului de pirită cu magnetit de la Altîn Tepe (Dobrogea centrală). II. Poziția stratigrafică a mineralizației. D. S. Inst. geol., LVIII/2 (1971), p. 25-51, București. Shadlum M. T. (1982) Ore Textures as Indicators of Formation Conditions of Mi- neral Paragenesis in Different Types of Stratiform Lead-Zinc Deposits. In : Ore Genesis — The State of the Art. Berlin. Stanton R. L. (1972) Ore Petrology. Mc Graw Hill, New York, p. 713. Suffel G. G., Hutchinson W. R., Ridler H. R. (1971) Metamorphism of Massive Sulphides at Manitonwadge, Ontario, Canada. Soc. Mining. Geol. Japan, Spec. Issue, p. 235-240 (Proc. IMA-IAGOD, Meetings, 270 IAGOD voi.). Vokes F. Mj (1969) A Review of the Metamorphism of Sulphides Deposits, Maniton- wadge, Ontario. Soc. Mining Geol. Japan, Spec. Issue 3, p. 235-240/Proe. IMA-IAGOD Meetings ’70, IAGOD voi.) Institutul Geological României Gisements PORPHYRY COPPER SYSTEMS IN THE SOUTH APUSENI MOUNTAINS — ROMANIA by SERGIU BOȘTINESCU 1 Introduction The Badenian-Sarmatian calc-alkaline magmatism in the South Apuseni Mts (Metaliferi Mts) evolved in an area with complex tectonic structure, consisting of Precambrian and Paleozoic metamorphic rocks, Mesozoic island arc ophiolites, Mesozoic deposits, Upper Cretaceous- Paleogene and pre-Badenian magmatites and Miocene deposits. The magma access ways, partly corresponding to the deep fractures bordering Miocene basins are most of all NW-SE oriented. Thus, several well individualized zones are delimited : Baia de Arieș, Roșia Montană- Bucium, Stănija-Zlatna, Căraciu-Brad-Săcărîmb and the Mureș Valley. The prevailing andesitic volcanism resulted in the emplacement of some explosive products and in the formation of a lot of simple or very complex apparata, partly preserved in certain places ; moderate- ly sized subvolcanic hodies have been emplaced at depth, typically by the end of the volcanic activity. Significant metallogenetic processes are related to the Sarmatian phase of this activity, resulting in some impregnations within andesitic bodies, breccias and host rocks, more or less complex vein systems, metasomatic replacements with metallic minerals ; gold-silver mineral- izations prevail at the upper levels, grading at depth to a dominantly lead-zinc character. The subvolcanic realm is characterized by mainly porphyry copper deposits, partly turned to account. Among these, the mineralizations from Deva (Borcoș et al., 1972) and Poieni (lonescu, 1974) have been initially ascribed to the porphyry copper type. The other occurrences, mainly identified during the se- venties, some by geophysical methods, have been the subject of local studies, among which those concerning the structures : Poieni (lonescu et. al., 1975 ; Petrulian et al., 1978), Bolcana (Udubașa et al., 1978 ; 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. A Institutul Geologic al României JGR/ S. BOȘTINESCU Boștinescu et al., 1980), Valea Morii (Borcoș et al., 1980) ; Musariu (Borcoș et al., 1980), Voia (Berbeleac et al., 1982), or with a regional synthesis character (lanovici et al., 1977 ; Boștinescu et al., 1981 ; Vlad, 1981 ; Andrei, 1981 ; Boștinescu et al., 1983). A general view of the porphyry copper mineralizations in the Metaliferi Mts may be outlined based on the present available geological data which are summarized here below. Main Features : Deva, Tarnița The porphyry copper structures in the South Apuseni Mts gene- rally have common features, but differ in some details, some of which suggesting two evolutionary trends — Deva and Tarnița ; the summary of their geological features is shown in Table 1. Distribution Excepting the northernmost structure — Baia de Arieș — the genetic conditions required for the generation of more or less evolved porphyry copper systems have been attained everywhere in the area where (Fig.) the Neogene volcanism occurs. Fig. — Synthetical model of a por- phyry copper structure. 1, metamorphites or ophiolites ; 2, Mesozoic and Neogene deposits; 3, early volcanites ; 4, subvolcanic body: a, axial zone ; 5, breccias, breccifiations ; 6, mineralized zone; 7, inner alteration zone ; 8, outer alteration zone; 9, veins ; 10, late andesitic flows ; 11, topographic surface during the emplacement time; 12, present-day topographic surface. Thus, in the Roșia Montană-Bucium Zone, the Poieni and Tarnița structures are known ; in the Stănija-Zlatna Zone : Valea Tisei, Măgura Poienii, Trimpoele ; in the Brad-Săcărîmb Zone : Rovina, Colnic, Musa- riu, Valea Morii, Bolcana, Voia ; in the Mureș Valley Zone : Deva. \ Institutul Geologic al României IGR/ 3 PORPHYRY COPPER SYSTEMȘ-APUSBNI MOUNTAINS 165 As a whole, the distribution of the porphyry copper systems in the South Apuseni Mts is confined to a NW-SE trending area, which extends towards the NW up to a line that joins Roșia Montană and Brad ; towards the SE, its limit passes near Zlatna and Deva ; the domain of porphyry copper occurrences is thus larger in the Mureș Valley and closes in the Baia de Arieș Zone. Geological Setting The upper levels of the basement of the zone with copper mine- ralizations consists of crystalline schists or ophiolitic formations, ap- parently the only important element differentiating them in what concerns the predating geological setting. This basement usually underlies Cretaceous sediments often in flysch facies, with ages ranging between Aptian and Senonian and Miocene detrital rocks. The above mentioned formations are crossed and overlain by the products of the Tertiary volcanism, represented by various intrusions and extrusions. It is frequently obvious that the porphyry copper structures are confined to the vicinity of faults, usually in their intersection points. In each case, the existence of at least one volcanic or subvolcanic episode, previous to the porphyry copper emplacement suggests the same ways of emplacement and the rather late genesis of the latter. The regional faulting sometimes favours the isometric character of the areal distribution of rootings. The mineralized intrusion occupies therefore a position near the axis of the whole zone. Thus, a central type structure appears, the development of some vein systems emphasiz- ing the above mentioned symmetry, as it is specially the case in the Poieni, Bolcana and Deva zones. The mineralized subvolcanoes seem to have finished their evo- lution which is strongly similar at comparable depths under the topo- graphic surface at the emplacement time. This evolution implies the appearance of some breccia formations. In the deep zones of some structures, the surrounding rocks have been modified by the thermal contact metamorphic processes. The alteration-mineralization processes favoured by characteristical cracks and brecciations are largely developed. The evolution of the magmatic phenomena in some porphyry copper structures is ended with the emplacement of some small sized intrusions. Petrography The petrographical features of rocks implied in the formation of porphyry copper structures vary between close limits. AU these rocks are andesites or quartz bearing andesites with hornblende whifle all the other mafics may be biotite and/or hyper- sthene, sometimes augite. The three main petrographic types — hornblende andesites, horn- blende andesites with biotite, hornblende andesites with pyroxene — Institutul Geological României 166 S. BOȘTINESCU 4 TA Main characters of porphyry coppcr Neogene pre-volcsmism formations Structural type Pclrographic types prc-orc volcanics | mincra- | lized por- 1 Phyry) post-orc volcanics 1 Poieni Macstrichtian flysch Campanian wildflysch Precambrian metamorphism central a am a am a am bi a am px 2 Tarnița ' Albian flysch Baric magmatites? a am a am unknown 3 Valea Tisei Albian flysch Ophiolitcs aam aam bi aam px aam unknown 4 Măgura Poienii Albian flysch Ophiolitcs aam aam unknown o Trîmpocle Miocene sediments Crctaceous deposits Ophiolitcs? aam a am unknown 6 Rovina Albian flysch Ophiolitcs a am a am px a am unknown 7 Colnic Albain flysch Ophiolitcs central a am a am px a am unknown 8 Musariu Badcnian sediments Albian flysch Ophiolitcs a ani a am bi a am px a am bi a am px 9 Valea Morii Miocene sediments Albian flysch Ophiolitcs a am a am bi a am px a am px unknown 10 Bolcana Miocene sediments Ophiolitcs Mctamorphitcs central a am a am bi a am a am 11 Voia 12 Deva Miocene sediments Ophiolitcs? Miocene sediments Turonian-Scnonian sediments Paleozoic metamorphism central a am bi a am a am bi a am a am bi a am a am a am px Abbrcviations : a-andesitc; fr-fresh: am-amphibolc; bi-biotite; px-pyroxcne; kf-potash fcldspar; cl-chlorite; act-actinotc; ep-epidotc; cm-clay minerals; ser-sericite; alu-alunite; anh-anhydrite: zc-zcolites; cp-chalcopyrite; py-pyrite; bn-bornile : mgt-magnetite ; cc-chalcosinc; ino-molybdenitc; po-pyrrhotine; ttr-tetrahedrite. Institutul Geologic al României PORPHYRYCOPPER SYSTEMS-APUSENI MOUNTAINS 167 BLE 1 Systems in the South Apuseni Mts Breccias, breccifi - ations Contact pheno- mena Alteration — mineralization Base metal veins Axial zone ) Inncr zone | Outer zone 1 importan 1 present frequent kf, bi, py, cp, mgt, mo, bn, ttr (anh, ze) cm, ser, py cm, py, alu minor impor- tant present frequent kf, el, act, py. cp. mgt, (anh) kf, cl, bi py. cp, mgt (anh) kf, cl, cp, py. cp, (anh) cl, cm, py cm, py presen t abun- dau t unknown kf, cl, bi, ep, act, py; cp cm, cl, ser, py abun- dant present i n s u f f i c i c n 11 y k n o w n present rescnt present 9 kf, cl, ep, act, bi, py, cp cm, cl, py present impor- tant unknown frequent kf, cl, act, py. mgt, cp, po, (anh) kf, cl, bi py. cp. mgt, po (anh) kf, cl, cp, py. cp, mgt, po, (anh) cl, cm, py arg, py present present unknown 9 kf, bi, act, ep, py, mgt, cp cm, cl, ser, py impor- tant present present kf, cl, ep, py, cp, act, bi el, cm, py cm, py abun- dau t present unknown kf, cl, act, ep, bi, py, cp, mgt, ru cl, cm, py cm, py abun- adnt presen t unknown kf, bi, cl, py, cp, mgt, bn, ru,(anh) cm, cl, py cm, py impor- tant present present kf, cl, ser, py, ep, (anh) cm, cl, py, alu impor- tant abun- dai! t brec- cia-pipe unknown frequent kf, bi, bn, cp, mgt, cc, (py, anh) cm, mgt minor Institutul Geological României 168 S. BOȘTINESCU 6 represent the early volcanites, the mineralized intrusion as well as the subsequent magmatic emplacement. Usually, the structures are typically porphyric, sometimes weakly expressed in the deeper zones. The coarse-grained structure of the mineralized subvolcanic bodies is the main feature which distinguishes them, when fresh, from the other intrusions. The mining works and mainly the two relatively deep drillings made in the Musariu and Deva structures which reached the absolute depth of approximately 1200 m, underline the gradual passage towards the porphyry microdiorite facies while in places the structures may be even dioritic. Fissurations, Brecciations An advanced fissuration, within a horizontally and vertically limited zone is characteristic for the mineralized intrusions. This zone is not generally found within sterile porphyries. The intensity of this phenomenon may be moderate, i.e. Tarnița, but can form crack-breccia aspects — Poieni and Bolcana breccias. The stockwork developed within the body on the Băilor Brook from Deva contains microfissures with orientations statistically con- formable to those of the two main faults in the area (NW-SE and WSW-ENE) which intersect each other in the ore zone, remembering the situation from Chaucha, Ecuador (Goosens, 1973). The subvolcanic intrusion border with host rocks mainly at up- per levels is the site of various brecciations, sometimes at microscopic scale. Fragments are angular to very rounded, consisting of andesites from the subvolcanic body, from the host rocks or both of the former and of the latter. The breccia matrix is only a small part of the rock body and is in făct represented by a microbreccia. At Rovina, some of the structural aspects suggest brecciation in a partly plastical stage of some local magmatic injections. At Poieni, Bolcana and Deva, some penetrations of fluid tuffitic material resemble those described in the Venice Alps (De Vecchi, De Zanche, 1974). Some of the features, mainly of the Bolcana structure, suggest a quite incipient breccia pipe type column. But at Deva the mineralized andesitic-microdiori'tic body has resulted into a breccia pipe consisting of variously sized andesite-microdiorite and host rocks fragments as well as an earlier breccia fragment. Several processes have been claimed for the genesis of such for- mations ; at Deva, the breccia pipe is the result of tectonic crushing described by Butler (1913) and Kuhn (1941), but mainly of the repeated collapse imagined by Perry (1961). Contact Phenomena In the neighbourhood of the subvolcanic intrusions, the deeper parts of the sedimentary host rocks may undergo the effects of contact metamorphism. Institutul Geological României \ 16 R/ PORPHYRY COPPER SYSTEMS_ APUSENI MOUNTAINS 169 The Albian formations at Tarnița and the Miocene rocks at Musa- riu and Voia (mainly their argillitic sequences) are affected in this way ; thus, some biotite hornfelses with a restricted areal development appear. The al terna tions consist of recrystallization of the primary minerals and the blastesis of minute biotite crystals, uniformly dispersed within the rock. Some more advanced stages of the metamorphic process have been revealed at Tarnița, resulting in andalusite and sillimanite bearing biotite hornfelses (Valentina Răduță, oral eommunication). Alteration — Mineralization The alteration processes display very well expressed zonality. mainly controlled by the distance from the intrusion axis and less by structural elements ; the lithologic control is less important. In the South Apuseni Mts, these processes, more than any other features, tend to discriminate between the Deva and Tarnița porphyry copper structures. The subvolcanic body axis corresponds to a discontinuous zone where the coarsely crystallized rock is practically unaltered. At Deva and Poieni andesites contain biotite with a deuteric aspect and at Tar- nița the axial zone has suffered a weak propilitization, mainly represent- ed by chloritization. Anyhow, for most of the mineralized intrusions belonging to the Tarnița type, the hydrothermal alterations seem to be superimposed over a previous late magmatic propilitization. Towards the outer zone we can outline two alteration areas equi- valent to those of feldspar stability and destruction respectively, pre- viously described by several authors. Within the inner zone corresponding to the potash silicate facies of the main genetic models (Lowell, Guilbert, 1970 ; Hollister, 1975 ; Hollister, 1978), the paragenetic assemblages of the Deva type contain potash feldspar and biotite, together with chalcopyrite, pyrite, bornite, magnetite, molybdenite, sometimes rutile, while at depth anhydrite and locally zeolites appear. The widely developed outer zone is characterized by the presence of clay minerals and pyrite. Sericite, which frequently appears in the argillization zone, some- times tends to be better represented towards its limit with the inner zone, which in the Poieni structure is more obvious ; this concentration corresponds to the phyllitic facies of the reference regions (Lowell, Guilbert, 1970), although it has not the same areal development and individualization. Alunite is formed within the argillization zone from Poieni and Voia. Institutul Geological României 170 S. BOȘTINESCU 8 Quartz is abundant in all alteration zones both as a metasomatic product and as veins. Pyrite has a characteristical behaviour in the Deva ore, being practically absent at middle levels of the mineralized column. For the Tarnița type, in the inner alteration zone the potash feld- spar and neoformation biotite are associated with chlorite. actinote, albite and epidote. Sometimes a zonal succession is obvious within this zone ; from the inner to the outer zone successively follow assem- blages with actinote, biotite and epidote, the albite being more important towards the borders. Anhydrite appears at depth, sometimes in large amounts. Metallic minerals are represented by pyrite (sometimes pyr- rhotite). chalcopyrite, magnetite ; bornite and molybdenite are very sub- ordinate or sporadic. In the outer zone, the main neoformations consist of clay minerals while pyrite is constantly present. Typical for the Tarnița type structures is the presence of chlorite in the argillization zone. Its concentration in the inner zone marks a subzone which could be as well an equivalent of the above mentioned phyllitic facies of alteration, when the iron excess characteristically modifies neoformation parageneses. Chloritization is sometimes very intense, and selectively emphasizes the primary structure of meta- somatized rocks. Quartz is also an ubiquitous hydrothermal product in this type of mineralization. Even in the inner alteration zone the argillization and sometimes sericitization processes generally affect tectonized rocks. Vein Mineralizations The mineralized intrusion is crossed mainly at Tarnița and Bol- cana by fascicles of veins or small veins with a predominantly lead- zinc character. They cross the copper mineralization and represent a final stage of the metallogenetic activity associated with the subvol- canic body. Otherwise, as for example at Musariu and Valea Morii, gold-silver veins are widely developed, belonging to complex systems, important at the metallogenetic district scale. In some structures of central type (Colnic and Bolcana), the vein systems have less clear relationships with the subvolcanic body. For the Bolcana veins, a zonality of gold-silver and base metal characters was delimited (Cioflica et al., 1966), whose inner term is identified in the copper rich nature of mineralizations associated with the subvolcanic intrusion. X. igrV Institutul Geological României 9 PORPHYRY COPPER SYSTEMS-APUSL'Nl MOUNTAINS 171 Geochemical Data Some geochemical features are typical for the porphyry copper mineralizations from the Metaliferi Mts. For example, the Sr/Ba ratiO' is constantly near 1, but concentrations of the two elements are higher for the Deva type. The Zn/Pb ratio is approximately 14, con ten ts in the Deva type being also higher ; the Deva ore is an exception,. as the Pb concentration is rather high (Zn/Pb = 3), In ores of the Deva Group the Mo/Cu ratio is high, while in those belonging to the Tarnița Group the values of the Au/Cu ratio increase. Thus, Kesler’s (1973) two classes of porphyry copper (CuMo and CuAu) are present ; the author attributes them to continental setting and to island arc setting respectively, which apparently correspond to the Deva and Tarnița types of the Metaliferi Mts. According to Sillitoe (1979), gold accumulation in porphyry copper deposits was favoured in the proximity of their present crustal setting. Although there are not proofs, the gold source of the Tarnița type porphyry copper could be related to the ophiolitic formations. As Sillitoe (1979), suggests, the concentration of gold in these ores is connected to the geochemical processes which determine iron enrich- ment within the feldspar stability field. Concluding Remarks The porphyry copper occurrences in the South Apuseni Mts, controlled by NW-SE fractures, are confined to a north-east trending zone, which parallels the main structural elements in the area. These occurrences show very similar essential features, but some aspects evidently separate them into two distinct trends, correspond- ing to the Deva and Tarnița types. The Poieni, Deva and to a lesser degree Bolcana structures be- long to the first type, while Tarnița, Valea Tisei, Trîmpoele, Rovina, Colnic, Musariu, Valea Morii and Voia belong to the second ; Măgura Poienii is not completely known. These two main types correspond to an ophiolite basement (Tar- nița) or to an area where ophiolites are absent (Deva). The structural, petrologie and alteration-mineralization features of the porphyry coppei’ systems in the Metaliferi Mts, mainly those of the Tarnița Group, are similar to several examples of island arc setting. They rnay hardly be matched in the known genetic models (Tab. 2). The Deva type resembles Lowell and Guilbert’s model, while the Tarnița type is ascribed to the dioritic model, with the difference that large areas of argillitic alteration occur in the Metaliferi Mts. Institutul Geological României \ 16 R/ 172 S. BOȘTINESCU 10 TABLE 2 .4 comparison between porphyry copper systems of the Metaliferi Mts and the main “porphyry copper” models Features 1 Lowcll and Guilbcrti Dioritic model model (after Hollister 1975) Metaliferi Mts Intrusion origin Mineralized intrusion quartz-granodiorite monzonite sienite-monzonite diorite Other present intrusions quartz-diorite diorite quartz diorite Alteration Central potash (orthoclase- potash (orthocla- potash (orthoclase-biotite; biotite and/or or- se-biotite and/or or- orthoclase-chlorite-acti- thoclase-chlorite) thoclase-chlorite) note-bioti te-epidote) Outside the central zone phyllitic (quartz- propilitic (chiori- argillitic (sometimes clay Outside the phyllitic zone Outside the argillitic zone sericite-pyrite) argillitic propilitic (chlorite- epidote) te-sericite or chio- ri te-epidote) mincrals-sericite or clay mincrals-chlorite) Diffuse pyrite in potash and phyl- in potash zone or in potash zone (except litic zones in both Deva) and in argillitic zone Mineralization Quartz in fissures common sporadic common Orthoclase in fissures common sporadic rare Albite in fissures traces common rare Magnetite scarcc common common (sometimes abun- dant) Pyrite in fissures common common common (except Deva) Molybdenite common rare sporadic Chalcopyrite/bornite ratio 3 or more 3 or less much more than 3 (subu- nitary at Deva) Chalcopyrite dissemina- tion present important present, sometimes im- portant Gold rare important impor tant Structurc Breccia-pipe type can appear rare column only at Deva Stockwork type important important common REFERENCES Andrei J., Calotă C. (1975) Etude geophysique des corps andesitiques de Roșia- Poieni et de Bucium-Tamița (Monts Metalliferes), â l’aide du modelage des sources des champs potentiels. Rev. roum. geol. geophys. geogr., Geophys., 19, București. Institutul Geological României 11 PORPHYRY. COPPER SYSTEMS—APUSENI MOUNTAINS 173 Berbeleac I., Zămîrcă A., David M., Vanghelie I., Ene I. D., Dumitrescu M., Astăniloaiei I. (1982) Report, archives of the Institute of Geology and Geo- physics, Bucharest. Borcoș M., Boștinescu I., Colios E., Mîndroiu V. (1972) Report, archives of the Institute of Geology and Geophysics, Bucharest. — Berbeleac I., Gheorghiță I., Bratosin I., Zămîrcă A., Anastase L., Verdeș Gr., Stănescu I. (1980) Geochemical Remarks on the Valea Morii Porphyry Cop- per Ore Deposit (the Metaliferi Mountains). D. S. Inst. geol. geofiz., LXIV, București. Boștinescu S., Vlad C., Bratosin I. (1980) Report, archives of the Institute of Geology and Geophysics, Bucharest. — Udrescu C., Anastase S. (1983) Report, archives of the Institute of Geology and Geophysics, Bucharest. Butler B. S. (1913) Geology and Ore Deposits of the San Francisco Region, Utah. V. S. Geol. Survey Prof. Paper, 80. Cioflica G., Jude R., Udubașa G. (1966) Caracterele structurale și mineralogice ale complexelor filoniene de la Măgura-Troița (Munții Metaliferi). St. cerc. . geol., geofiz., geogr., Geol., 11, București. Goosens P. J. (1973) Structural Control and Hydrothermal Alteration Pattern of Chaucha Porphyry Copper, Ecuador. Mineral. Deposita, 8. Hollister V. F. (1975) An Uppraisal of the Nature and Source of Porphyry Copper Deposits. Min. Sci. En., 7. — (1978) Geology of the Porphyry Copper Deposits of the Western Hemisphere. AIME, New York. lanovici V., Vlad I., Borcoș M., Boștinescu S. (1977) Alpine Porphyry Copper Mineralization in West Remania. Mineral. Deposita, 12. lonescu O. (1974) Mineralizația cupriferă de tip diseminat de la Roșia-Poieni (jud. Alba). St. cerc, geol., geofiz., geogr., Geol., 19, București. — Soare C., Gheorghiu M. (1975) Contribuții la cunoașterea zăcămîntului cu- prifer Roșia-Poieni. Alterații hipogene. St. cerc, geol., geofiz., geogr., Geol., 20, București. Kesler S. E. (1973) Copper Molybdenum and Gold Abundances in Porphyry Copper Deposits. Econ. Geol., 68. Kuhn T. H. (1941) Pipe Deposits of the Copper Creek Area, Arizona, Econ. Geol., 36. Lowell J. D., Guilbert J. M. (1970) Lateral and Vertical Alteration Mineralization Zoning in Porphyry Ore Deposits. Econ. Geol., 65. Petrulian N., Steclaci L., Jude R., Popescu R., Cioran A. (1978) Contribuții la studiul mineralogic și geochimic al mineralizației cuprifere de la Roșia- Poieni (Munții Metaliferi). St. cerc, geol., geofiz., geogr., Geol., 23, București. Sillitoe R. H. (1979) Some Thoughts on Gold-Rich Porphyry Copper Deposits. Mineral. Deposita, 14. , Institutul Geologic al României 174 S. BOȘTINESCU 12 Udubașa G., Istrate G,, David M., Neacșu V., Bratosin I., Vanghelie I-, Andăr P. (1978) Study, archives of the Institute of Geology and Geophysics, Bucharest. Vecchi G. De, Zanche V. De (1974) Fluidization and Tuffization in the Western Venetian Alps. Boli. Soc. Geol. It., 93. Vlad Ș. (1981) Monoascendant and Polyascendant Porphyry Copper Systems. Rev. roum. geol., geophys., geogr., Geol., 25, București. Institutul Geologic al României S. BOȘTINESCU- Porphyry Copper Systems - South Apuseni Mountains DISTRiBUTION OF PORPHYRY COPPER OCCURRENCES IN THE SOUTH APUSENI MOUNTAINS Imprim.Atei -In st-Geol.Geof ANUARUL INSTITUTULUI DE GEOLOGIE Șl GEOFIZICĂ. VOL. LXIV -X'_:A Institutul Geological României \IGRZ Gisements ALPINE METALLOGENY IN ROMANIA BY GRAȚIAN CIOFLICA ', ȘERBAN VLAD 2 Introduction The purpose of this paper is to discuss metallogeny in association with the evolution of tectonics and magmatism during Alpine time on the Romanian territory. It provides therefore an outlook on the metal- logenetic development during a complete cycle by taking into account the ore types associated with successive intracontinental rifting (North Dobrogea, Ditrău), spreading areas (South Carpathians), subduction related settings (South Apuseni Mts, East and South Carpathians), collision and post-collision related settings (East and South Carpathians, South Apuseni Mts) (Fig. 1). Metallogenesis Related to Intracontinental Rifting The Ditrău alkaline massif (East Carpathians) with related car- bonatites and associated Mo ores was emplaced in a Mesozoic intra- continental rift. The alkaline massif is a quasi-ring-like intrusive (Anas- tasiu, Constantinescu, 1980) and exhibits a complex structure : the innermost part is built up of foid rocks, surrounded discontinuously by syenite and monzonite rocks ; hornblendite and diorite rocks are confined to the north-western margin of the composite pluton, and granites and alkali granites occur especially at the contact with the basement (Fig. 2). These rocks belonging to the main magmatic event are associated with lamprophyre, microsyenite, even foid, alkali granițe and aplite dykes. Albitite segregations and carbonatic veins with sulphide minerals are found in places. Mo-bearing carbonatites are developed commonly as veins, but also as nests, bands, veinlets and dissemina- tions. Carbonatites and related ores formed discontinuously from the late ortho-magmatic to the hydrothermal stages. In the north (Constan- tinescu et al., 1983) ilmenorutile, ilmenite, monazite, tapiolite. columbite and sulphide minerals are the characteristic association within diorite and hornblendite rocks. whereas xenothime, sulphides and niobotan- talates are common within alkali syenite rocks found in the eastern and Southern parts of the massif. 1 University of Bucharest, Department of Geology, Bd. N. Bălcescu 1, 70111 Bucharest. 2 Ministry of Geology, str. Mendeleev 36—38, 70169 Bucharest. ' a Institutul Geologic al României JGR/ Fig. 1 — Distribution of Alpine magmatism in Romania (modified from Cioflica et al., 1980). 1, short-lived rift-related igneous rocks ; 2, ocean floor spreading-related igneous rocks ; 3, subduction-related Mesozoic (Lower Jurassic-Neocomian) magmatism ; 4, subduction-related Senonian-Paleocene magmatism (banatites) ; 5, subduction-re- lated Neogene volcanics. TCF, Transcarpathian flysch ; CN, Central East Car- pathian Nappes ; BF, Black Flysch nappes ; Tn, Transylvanian Nappe ; Ch N, Ceahlău Nappe ; FN, Flysch Nappe ; IFM, inner flank of molasse; OFM, outer flank of molasse ; SGN, Supragetic Nappe ; GN, Getic Nappe ; SN, Severin Nappe ; DA, Danubian Autochthon ; NAM, North Apuseni Mountains ; SAM, South Apuseni Mountains ; TD, Transylvanian Depression ; ND, North Dobrogea orogenic system ; EP, East European Platform ; MP, Moesian Platform. Fig. 2 — Geology and struc- ture of the Ditrău alkaline mas- sif (acc. to Anastasiu, Constan- tinescu, 1980). 1, hornblendite ; 2, diorite; 3, syenite, alkali syenite, monzo- nite, monzodiorite; 4, foid rocks ; 5, granițe, alkali gra- nițe ; 6, carbonatites with re- lated ores ; 7, faults. 3 ALPINE METALLOGENY IN ROMANIA 177 The North Dobrogea area evolved during Alpine times as an aulacogen-like failed arm in xelation with active rifting developed into the Tethys Ocean (Vlad, 1978). It became. inactive before reaching the stage of ocean-floor spreading and was filled by clastics and, especially, carbonate prevailing sediments. The lower part of the sedimentary suc- cession was penetrated by bimodal (basaltic-rhyolitic) magmatism. The mineralization is stratabound within Spathian calcareous-terrigenous turbidites penetrated by volcanics. It consists of carbonate-hosted and, of lesser extent, rhyolite-associated ores as follows : stratiform sedi- mentary barite bodies formed within minor submarine depressions ; small Ba + Pb-Zn veins in steeply dipping fractures mostly along the crests of anticlines ' restricted Fe-bearing infiltration skarns in the vicinity of the Luncavița-Consul Line ; Pb-Zn + Ba, F stockworks in K-altered rhyolites. Metallogenesis Related to Ocean Floor Spreading Areas Ophiolites of the South Carpathians are related to the Severin Nappe. They were considered of ocean floor type according to geo- dynamic interpretations (Rădulescu, Săndulescu, 1973). An elongated basin with oceanic crust acted between the Getic and the Danubian realms. It promoted basaltic flows and pyroclastics associated with Lower Sinaia Beds during Lower Cretaceous times. The Severin Nappe which contains them is tectonically emplaced between the Getic Nappe and the Danubian Autochthon. It migrated completely from the roots during Upper Cretaceous compressions, when collision between Getic and Danubian realms was reached. The metallogenesis related to these obducted ophiolites yielded Cu-pyrite ores at Baia de Aramă. Cioflica et al. (1981) provided geological and geochemical evidence to characterize these ophiolites as tholeiitic ocean floor basalts formed in a small ocean setting. A$pordingly the related ore deposition was ascribed to the Joma type of Pearce and Gale (1977). The Cu-pyrite ores are located in a lava unit of prevalent basaltic character. The basalts that exhibit in places pillow structure contain small size stratiform pods of massive chalcopyrite, with subordinate amounts of early pyrite and subsequent sphalerite in quartzose gangue'. The massive ore is commonly underlain by pyrite + chalcopyrite, sphalerite stockworks (Fig. 3). Fig. 3 — Section through mi- neralized ophiolites from Baia de Aramă (acc. to Cioflica et al., 1980). 1, crystalline schists of the Getic Nappe ; 2, serpenWnite protrusion ; 3, ophiolite complex (a, upper ophiolites ; b, lower ophiolites ; c, mineralization) ; 4, Cretaceous black argillite; 5, Sinaia Beds ; 6, Upper Creta- ceous flysch of the Danubian Unit; 7, thrust ; 8, fault. 12 — C. 6«7 Institutul Geological României 178 GR. CIOFLTCA, Ș. VLAD 4 Metallogenesis of Subduction-Related Settings The Mesozoic magmatic rocks of the South Apuseni Mts are loca- ted between crystalline schists of the North Apuseni Mts and of the South Carpathians. They derived from .a tri-stadial magmatism, that is first stage-tholeiite series (Lower Jurassic-Callovian) and second stage-calc-alkaline series (Upper Callovian-Neocomian) representing island arc magmatism, and third stage-spilitic complex (Barremian- Lower Aptian ?) representing active marginal basin magmatism (Cioflica et al., 1980). The related metallogenesis consists of Fe-Ti-V and Ni late mag- matic segregations in gabbroic intrusions and Cu-pyrite veins and stockworks in basaltic lavas of the tholeiite series, whereas the calc- alkaline series comprises Mn volcano-sedimentary ores. The Fe-Ti-V segregations occur in layered gabbroic bodies (e.g. Căzănești-Ciungani) as nests, lenses and disseminations consisting of titanomagnetite and ilmenite. The Ni ores are found at Ciungani where a small size metallic pod contains pyrrhotite, pentlandite and sporadic chalcopyrite and magnetite. The Cu-pyrite volcanogenic ores associate with bașalts and fall in the Gjersvik type of Pearce and Gale (1977) (Cioflica et al., 1981). At Pătîrș (Fig 4) the mineralization consists of pyrite + chalcopyrite veinlets and a massive pyrite pod, surrounded by a disseminated pyrite halo. At Căzănești-Ciungani, Almășel, Roșia Nouă, Corbești and Pietriș similar Cu-pyrite ores (veins, stockworks) are controlled by various fractures and' brecciated basalts. Mn volcano-sedimentary ores are as- sociated with jaspers at Șoimuș-Buceava-Pîrnești and Godinești. The Senonian-Paleocene calc-alkaline magmatic belt (banatites) related to distinct subduction-related settings runs from the Apuseni Mts to the South Carpathians. The magmatic emplacement was tecto- nically controlled and exhibits a specific polystadial character : 1) vol- canics consisting of andesite, dacite, rhyolite rocks and associated pyro- clastics ; 2) subsequent intrusive stage divided into three phases : a) early minor diorite bodies ; b) plutons and subvolcanic bodies of monzo- diorite, diorite -> granodiorite and granodiorite granițe composi- tion ; c) final acidic dykes and concurrent basic and lamprophyre dykes. The intrusions of the main intrusive event were accompanied by recrystallization and metasomatism. The latter produced significant re- placement zones with widespread mineralization inside and around Fig. 4 — Section through mi- neralized ophiolites from Pătîrș (acc. to Cioflica et al., 1980). 1, ophiolites (a, unmineralized ; b, pyrite impregnations ; c, pyrite -j- chalcopyrite stock- work) ; 2, Gossan ; 3, Creta- ceous flysch ; 4, reversed fault. Institutul Geological României O ALPINE METALLOGENY IN ROMANIA 179 bodies of the main magmatic event of subsequent dykes. Porphyry cop- per of Lowell and Guilbert type and skarn deposits prevail, whereas vein deposits occur scarcely (Cioflica, Vlad, 1980) (Fig. 5). The North Apuseni Mts sub-belt is characterized by major grano- diorite — granițe magmatism and widespread base metal deposition. Fig. 5. — Distribution of the Senonian-Paleocene magmatism and ore deposits in Romania (acc. to Cioflica, Vlad, 1980). 1, igneous bodies belonging to the granodiorite -> granițe evolution line : a, plutons and subvolcanic bodies ; b, volcano- plutonic complex ; 2, igneous bodies (plutons and subvolcanic bodies) belonging to the monzo- dioritic, dioritic -> granodiori- tic evolution line ; 3, petrogene- tic alignment. ; 4, Banat-Poiana Rusca Mts sub-belt ; 5, Drocea- Metaliferi Mts sub-belt; G, North Apuseni sub-belt; 7, Cu-Pb line ; 8, complex-Pb, Zn line ; 9, direction of subduction. E r w UT A 3 C 0 1 ! 3 4 f 6 ’l io rl The well-expressed zoning is represented by the complex zone of the Bihor-Gilău (Mo, Bi, W, Cu, Co, Ni, Pb, Zn, B and Fe ores assoeiated with skarns), followed landwards by the base metal zone (hydrothermal Pb-Zn ores in the Vlădeasa Massif and Cornițel-Borod Depression). The South Apuseni Mts sub-belt with transverse position with regard to the adjacent Banat-Poiana Ruscă and North Apuseni Mts sub- belts is represented by monzodiorite, diorite -> granodiorite magmatism with Cu-impregnated and Fe skarn deposits and granodiorite -> granițe magmatism with Pb-Zn and Mo vein deposits. The Banat-Poiana Ruscă Mts sub-belt is represented by the inner zone (South Banat) with monzodiorite, diorite -> granodiorite mag- Institutul Geological României 180 GR. CIOFLICA, Ș. VLAD 6 matism and Cu-Mo porphyry and skarn deposits (e.g. Moldova Nouă), and landward, by the outer zone (North Banat-Poiana Ruscă) with gra- nodiorite -> granițe magmatism and Fe, Pb-Zn skarn deposits (e.g. Dognecea, Ocna de Fier) or restricted Mo-porphyry occurrences (e.g. Oravița). The well expressed Cu(Mo) -> Mo -> Fe, Pb-Zn transverse zoning is characteristic of the Andean-tvpe subduction related setting (Vlad, 1979). The Neogene magmatism consists of calc-alkaline products of mainly andesitic type related to westward subduction of the eastern Fig. 6 — Deposits in 1, Neogene magmatism the South Apuseni Mountains (modified from Giuseă et al., 1969). (necks, dykes ; lavas not represented) : 2. Miocene molasse ; 3, pre-Tertiary basement ; 4, veins ; 5. porphyry copper ; 6. faults. basin (Rădulescu, Săndulescu, 1973). It developed within the inner part of the Carpathians (Fig. 1) and consists of the East Carpathians volcanic arc and volcanic occurrences along NW-SE and E-W alignments within the mature island arc structure of the South Apuseni Mts. Subvolcanic bodies which penetrated the volcanics promoted recrystallization of surrounding rocks as well as metasomatism. The related metallogenesis is of hydrothermal type and yielded commonly Au-Ag, base metal and Cu ores with subordinate amounts of Hg, exhalative S and Fe (siderite) (Giușcă et al. 1969 ; Borcoș et al., 1980). The ores occur commonly as veins and stockworks which are intimately controlled by fractures and breccia pipes. The South Apuseni Mts (Fig. 6) are characterized by Au-Ag veins and stockworks ; they are found within volcanics and associate with Institutul Geological României \ ig rZ ALPINE METALLOGENY IN ROMANIA 181 base metal veins, porphyry copper Systems of stockwork or breccia- pipe type and peripheral Hg occurrences. The host volcanics filled tec- tonically controlled Tertiary sedimentary basin which crosses the ma- ture Mesozoic island arc. Porphyry copper deposits are of peculiar character for the Tertiary metallogeny and were assigned to the diorite model (lanovici et al., 1977). They contrast with the Senonian-Paleo- cene systems by lack of skarnization halo replaced by peripheral Au-Ag and Pb-Zn. The porphyry systems show a Cu-Au character (Tarnița, Rovina, Valea Morii, Musariu) and a Cu-'Mo(Au) character (Deva, Roșia Poieni). Fig. 7 — Deposits in the Oaș-Gutii Mountains (modified from Giușcă et al., 1969). 1, Neogene volcanics ; 2, Neogene molasse ; 3, Paleogene flysch ; 4. veins, stock- works ; 5, fault; 6, overthrust ; 7, anticline axis. The Southern margin of the Gutîi Mts contains significant ore deposits (Fig. 7). In the northern part of the Oaș Mts mineralizations occur between Tarna and Bicsad. In these regions base metal veins prevail ; it is noteworthy that the deeper parts of this setting may promote porphyry copper metallogeny. In the Țibleș-Toroiaga Mts sulphide mineralization is related to subvolcanic bodies, whereas in the Rodna Mts they connect with breccia pipes or replace crystalline limestones. In the Harghita-Gurghiu-Călimani Mts only Hg, S, Fe (siderite) and restricted Au-Ag and base metal ores are known up to the present. It is however likely that porphyry copper systems may develop at depth (Peltz et al., 1982). 182 ALPINE METALLOGENY IN ROMANIA Metallogenesis of the Passive Margin-Related Settings The sedimentary Fe deposit from Căpuș occurs within epicon- tinental sediments found north of the Gilău crystalline massif, as limo- nitic and glauconitic ores (Vinogradov et al., 1963). Metallogenesis of the Continental Collision-Related Settings In the eastern part of the South Carpathians, Supragetic (East Făgăraș Mts) and Getic crystalline schists (Leaota Mts) are cut in spe- Fig. 8 — Continent-continent col- lision-related ore deposition in the eastern South Carphathians (acc. to Vlad, Dinică, 1984). 1, continent-continent collision-re- lated granite-alkaline granițe plu- ton ; 2, continental crust ; 3, up- per mantie; 4, Lower Cretaceous flysch + obducted ophiolites ; 5, molasse ; 6, ores (a, Co-Ni ; b, base metal ; c, gold). cific areas by numerous minor veins that contain Bi minerals, Co-Ni sulphides and arsenides, base metal minerals and gold. The spațial distribution of the ores strongly suggests a periplutonic arrangement within the contact aureole of two presumed deep-seated plutons. Re- gionally, the ore occurs along a NNE-SSW alignment which is to be related to the above mentioned plutons ; accordingly, it is however li- kely that a deep-seated continent-continent collision belt of Erzgebirge or Cornwall type runs in the east South Carpathians (Vlad. Dinică, 1984) (Fig. 8). Metallogenesis Related to Post-Collision-Related Settings At Jitia (East Carpathians) base metal ores of diagenetic and partly epigenetic nature are found within Miocene sediments. Conclusions The Alpine ore deposition in Remania was intimately connected with magmatic and other controlling factors during the Mesozoic- Cainozoic cycle of early intracontinental rifting, ocean floor spreading, subduction, continental collision and post-collision rifting. Unevolved settings were assigned to the early intracontinental rifting. The North Dobrogea aulacogen-like Trough exhibits a charac- teristic Triassic bimodal magmatism and Ba-Pb-Zn and Fe metallo- geny ; the metals resulted by means of concentration from the sialic crust during rifting and hot brines formation. The Ditrău alkaline pluton and associated carbonatites with Mo deposits, occurred above a ther- mal dome in continental environment ; it is likely that Mo and associa- ted metals were subtracted from the sialic crust by the alkaline melts. <) GR. CIOFLrCA, Ș. VLAD 183 Various evolved settings promoted significant metallogenesis during Alpine times. The deposits formed in oceanic setting are repre- sented by Cu-pyrite volcanogenic ores from Baia de Aramă (South Carpathians). Subsequent compressions yielded various deposits related to pulsative subduction events. Thus, the closing of the South Apuseni Mts basin gave rise to island arc volcanics with associated deposits : Fe-Ti-V and Ni late magmatic segregations, Cu-pyrite volcanogenic ores. Following the suture of the island arc to the North Apuseni Mts sialic block, sedimentary Fe deposits formed on the north-western pas- sive continental margin of the paleo-basin. A rather complex subduction which promoted also an Andean type magmatic arc in Banat-Poiana Ruscă gave rise to banatitic igneous rocks and associated metallogenesis. During the main magmatic event two evolution lines developed differentially. The monzodiorite, diorite granodiorite acted as Cu carrier from the deep-seated source, that is upper mantle-subducted oceanic crust. The granodiorite gra- nițe magmatism mobilised various metals from the sialic crust by palyngenesis ; it is situated landwards and yielded Mo, base metal 'deposits. The Tertiary subduction inferred from specific evidence gave rise to externai andesite arc (East Carpathians) with Au-Ag and base metal metallogenesis and to internai andesite occurrences (South Apuseni Mts) wherein Au-Ag and porphyry copper metallogenesis prevails. It is to be mentioned that Cu metallogenesis sequences derived from deep-seated sources (upper mantie, subducted oceanic crust) taking into account both scale metallogeny and ore formation within restricted deposits (e.g. porphyry systems and the Baia Sprie xenothermal de- posits). Pb-Zn, Mo, Au-Ag sequences derived simultaneously from sialic environments by palyngenesis. The higher Au contents of South Apu- seni Mts mineralizations are presumably due to remobilisation from island arc tholeiites, too. Co, Ni, Bi, Ag, Au, Cu mineralizations and related magmatic- tectonic features from the Leaota-Făgăraș Mts provide evidence for interpreting such settings as continental collision magmatism and rela- ted metallogenesis. The post-collisional event of the Southern East Carpathians promoted sedimentary Pb-Zn metallogenesis at Jitia, in connection with the Lower Miocene molasse. Finally, intracontinental basalts (7,3 + 0,6 m.y, according to Rădulescu et al., 1981) are charac- teristic of late post-collisional rifting and lack in metallogenetic im- portance. REFERENCES Anastasiu N.. Constantinescu E. (1980) Structure du massif alcalin de Ditrău, Anal. Univ. București, XXIX. Borcoș M., Peltz S., Stan N., Berbeleac I. (in press) Neogene and Permian Vol- canism in the Apuseni Mountains and the East Carpathians. D. S. geol. geofiz., LXVIII/1, București. jA, Institutul Geologic al României igr/ 184 ALPINE METALLOGENY IN ROMANIA 10 Cioflica G., Vlad Ș. (1980) Copper Sulphide Deposits Related to Laramian Mag- matism in Romania. European Copper Deposits, Betgrade. — Lupu M., Nicolae I., Vlad ,Ș. (1980) Alpine Ophiolites of Romania: Tec- tonic Setting, Magmatism and Metallogenesis. An. Inst. geol. geofiz.. LVI, București. — Vlad Ș., Nicolae I., Vlad C., Bratosin I. (1981) Copper Metallogenesis Re- lated to Mesozoic Ophiolites from Romania. Symp. Mafie Ultram. Compl., Athenes 9—11, 1980, IUGS Pr. no. 169, 2. Constantinescu E., Anastasiu N., Garbașevschi N., Pop N. (1983) Contribution â. la connaissance des aspects paragenetiques de la mineralisation associee au massif alcalin de Ditrău. An. Inst. geol. geofiz., LXII (Trav. Xlle Congr. Assoc. Geol. Carp.-Balk.), București. Giușcă D., Cioflica G., Udubașa G. (1969) Metallogenesis Associated to Neogene Volcanism in the Romanian Carpathians. Rev. roum. geol. geophys. geogr., Geol., 1, București. lanovici V., Vlad Ș., Borcoș M., Boștinescu S. (1977) Alpine Porphyry Copper Mineralization of West Romania. Mineral. Deposita, 12. Pearce J. A., Gale G. H. (1977) Identification of Ore Deposition Environment from Trace Element Geochemistry of Associated Igneous Host Rocks. In. Voie. Proc. in Ore Genesis. Inst. Min. Met. Geol. Soc., London. Peltz S., Peltz M., Botar N. (1982) Observații litogeochimice și implicații metalo- genetice în aria vulcanică Găineasa (craterul Seaca-Tătarca, Munții Gur- ghiu). D. S. Inst. geol. geofiz., LXVII,'2 (1979—1980), București. Rădulescu D. P., Săndulescu M. (1973) The plate Tectonics Concept and the Geological Structure of the Carpathians. Tectonophysics, 19, 3, Amsterdam. — Borcoș M., Peltz S., Istrate G. (1981) Subduction Magmatism in Romanian Carpathians. Guide to Excursion A 2. Carp.-Balk. Geol. Assoc. 12th Congr., Bucharest. Vinogradov C., Barbu I. Z., Hesselman A. (1963) Contribuții la cunoașterea zăcă- mintelor sedimentare de fier de la Căpuș (reg. Cluj). St. cerc, geol., Acad. RPR, 2, București. Vlad Ș. (1978) Metaiogeneza triasică din zona Tulcea (Dobrogea de nord). St. cerc, geol., geofiz., geogr., Geol., 23, București. — (1979) A Survey of Banatitic (Laramian) Metallogeny in the Banat Region. Rev. roum. geol. geophys. geogr., Geol., 23, București. — Dinică I. (in press) Mineralizațiile filoniene din cristalinul de Leaota. Con- siderații preliminare. St. cerc. geol. geofiz., geogr., Geol., București. Gisements THE TECTOSTRUCTURAL FACTOR, A FUNDAMENTAL CRITERIUM TO OUTLINE THE METALLOGENETIC (PETROMETALLOGENETIC) PROVINCES — EXEMPLIFICATION ON THE ROMANIAN TERRITORY BY IOAN MÎRZA 1 The first observations and studies on provinces and metallogene- tic epochs were made at the beginning of our century ; this idea was developed by de Launay (1913) in Europe, Emmons (1913) and Spurr (1923) in America. Subsequently, many other researchers dealt with this question which became not only interesting, but also useful. Among them, we can speak of Stanciu (1930), Lindgren (1933), Blondei (1938), Hills (1947), Turneaure (1955), Bateman (1956), Routhier (1963), Pe- traschek (1965), Jankovic (1967), Vokes (1971), etc. The Soviet geolo- gists had an important contribution to this question, starting by Obrucev, Fersman, and continuing by Smirnov, Bilibin (1955), Smirnov (1959), Magakian (1959, 1967), Tatarinov (1967) and others. The notions of province, its subunits (sub-province, district, me- talliferous field, deposit, ore body), and metallogenetic epoch are widely discussed in literature, but without finding a common reference point for all cases, in order to define their content. We consider the metallogenetic provinces as geostructural spațial units, remarked by a structogene evolution, magmatism and specificai metallogeny, and the metalogenetic epochs as geochronological sequences during which metallization took place. A new stage in the study and interpretation of metallogenetic provinces is connected to the idea of general tectonics, to which many researches had important contributions (Noble, 1970, 1974 ; Turneaure, 1971 ; Sillitoe, 1972 ; Closets, 1972, etc.). According to this theory, the metallogenetic provinces are some spațial units which reflect the geostructural domain where petrometal- logeny manifests itself, by outlining for the magmatic domain : pro- vinces of lithosphere compression ; provinces of compression zones (sub- duction), namely the Alpine type and the island arc type ; provinces of the hot regions, the oceanic type (weaklier expressed) and the con- 1 „Babeș-Bolyai“ University, str. Kogălniceanu 1, Cluj-Napoca. < M Institutul Geologic al României 186 I- MIRZA tinental type. Here, the metallogeny of the tectono-magmatically acti- va ted zones can be added (Șceglov, 1979). According to the geological time of formation, we can separate pangeic (petrometallogenetic) metallogenetic provinces, whose genesis is previous to the detachment of the metallized surface from the origi- nating continent, and post-pangeic ones, formed after the detachment of the continental plates from the primitive block. The result is the migration of the metallogenetic provinces, what de Closets (1972) has called “la derive des gisements” (the deposit drift). Provinces and Magmato-Metallogene Epochs on the Romanian Territory Long time after the first study of professor Stanciu (1930), entitled “The mineral provinces of Romania”, the problems of the relationship between the metallization time and space of the Romanian territory were a theme requested by many geologists (Socolescu, 1961 ; Dimi- trescu, 1961, 1972 ; lanovici et al., 1966 ; Rădulescu, 1966 ; Rădulescu et al., 1970 ; Lucea, 1967 ; Codarcea-Dessila, 1968 ; Savu et al., 1970 ; Giușcă, 1974 ; Mârza, 1981, 1982). The tectonic-magmatism-metallization causality relationship im- poses the substantiation of the concept of magmato-metallogenetic (or metallogenetic) province on the tectostructural criterium ; in this case, the activated mobile or stable tectonic structures are the origin of magma formation and concentration. The largest tectostructural zones of the earth crust correspond to the magma to-metallogene belts ; pro- vinces and sub-provinces, etc. are encompassed by their segments (sub- divisions). From the funcțional type point of view, the geostructures activate as spreading zones, compression zones and stable zones, each with characteristical magmatism and associated metallogeny. According to the geostructural criterium, which was substantiated on general tectonics concept (Rădulescu, Săndulescu, 1973 ; Bleahu et al., 1973) the following provinces associated with the geostructural units (petrometallogene) of the Romanian territory are to be mentioned (Mârza, 1982) : provinces of stable units ; provinces of mobile units ; provinces of rift zones ; provinces of subduction zones. Taking into account the common geological evolution of the boun- dary territories between Romania and the neighbouring countries, the formation of metallogenetic (petrometallogenetic) provinces was regar- ded in a unitary framework (Fig.). Provinces of Stable Zones 1. The province of the East European Platform : the Moldavian Platform sub-province ; 2. the Moesian Platform province : the Wal- lachian sub-province ; the South Dobrogea province ; the Central Do- brogea sub-province. Provinces of Mobile Zones 3. The Carphathian Crystalline province : the East Carphathians sub-province ; the South Carpathians sub-province ; the Apuseni Mts province ; 4. the North Dobrogea Orogene province. M Institutul Geological României icRy 3 TECTOSTRUCTURAL FACTOR METALLOGENETIC PROVINCES 187 Provinces of Rift Zones (Riftogene) 5. The Balkan province of gabbro-peridotitic complexes : the North Danubian sub-province of Paleozoic ultrabasic magmatites, be- longing to the Balkan-Anatolian-Iranian (Tethys) magmato-metallogene belt. corresponding to the Paleozoic and old Alpine ultrabasic magmati- tes (over 4000 m) ; 6. The metallogenetic province associated to the Mesozoic ophiolitic magmatism from the Apuseni Mts : the Highiș sub- province, sulphide mineralizations ; the Drocea-Mureș sub-province ; the Trascău sub-province. Provinces of Subduction Zones (Subductogene) 7. The metallogenetic province associated to the banatitic (La- ramian) magmatism ; it belongs to the Dacian-Balkan-Transcaucasian- Iranian Belt, associated to the Laramian magmatism and developed on about 4500 km long : the Banat sub-province ; the Poiana Ruscă sub- province ; the Apuseni Mts sub-province ; 8. The metallogenetic pro- vince of the Carpathian neoeruptive chain : the Bbrzsbny-Zempleny (Tokaj) sub-province in Hungary ; the Vihorlat (Czechoslovakia)-Gutin sub-province ; the Toroiaga-Căliman-Harghita sub-province ; 9. The metallogenetic province associated to the neo-magmatism from the Apuseni Mts, characterized by native gold deposits (telluriums), porphyry copper and less polymetallic ones : the Arad-Săcărîmb district ; the Stăniia-Zlatna district ; the Roșia Montană-Bucium district. The Baia de Arieș metallogenetic field. Main Metallogenetic Epochs on the Romanian Territory The geological evolution of the Romanian territory has numerous phases or epochs with magmato-metallogene activity, which took place from the Precambrian to the Pliocene (Tab.). The Precambrian epochs belong to the Prebaikalian epoch (Cadomian). The basic idea with important metallogenetic significances presen- ted in this paper is considered to be the connection of the endogene (petrometallogene) metallogenetic provinces with the geostructural units which from a unitary type of developing the geological processes ; ac- cording to their genotype, both the petrogenesis and the associated metallogeny are pointed out by distinct notes (chemism, mineralogy, metallogenetic phase, deposit form, etc.). The geostructural individua- lity of metallogenetic provinces is marked as well by metallization (or petrometallogene) epochs. Therefore, there are monocyclic and polycyclic regions, the latter being tectono-magmatically reactivated during various phases. In a geostructure, the epochs alternate in time and superpose in space. Institutul Geological României Main endogene metaUogenetic epochs corresponding to prooinces of ihe Romanian territory and generated mineral resources Institutul Geological României Bălrina and volca- nogene-scdimenta- ry series Carboniferous Someș Series , f Biharia Series Reflected metallo- geny Au-Valea lui Stan (Lotru) Fe-(oxidc-carbonatic) Poiana Ruscă Sulphides (Pb-Zn), Mun- celul Mic-Muncehil Mare- Velcl (Poiana Ruscă) Talc dolomites (Poiana Ruscă) ultrabasites (Cr, Ni, Pt), Sebeș Mts and Almăj t c matites (Gilău Mts) Sulphides (Pb—Zn±Cu), Sirrin rl-1 barili 1 oln deasa) Metabasitcs with magne- tite, ilmenite, chalcopy- rite (disseminations) Mainly hydrothermal mi- neralizat ions associated with medilic magmatites locatcd in crystalline (Trascău-Băișoara, Ciu- cea-Remeți) Complex sulphides in the sedimentary border (Băi- șoarasector) Pegmatites, migmatites Magnetitc-hematile, su- Dordinatcly sulphides (lu- lia), sulphides (Pb-Zn), barite (Somova- Minerii) 1 Cr (Banat) Asbestos (Banat) Hydrothermal (me- tamorphosed) volcanogene-sedi- menlary Hydrothermal- metamorphic Orthomagmatic Metamorphic Volcanogene-sedi- Orthomagmatic Hydrothermal Metamorphic Hydrothermal skarn Hydrothermal Orthomagmatic Hydrothermal-me- tamorphic Island arc(?) ff Orogene Tectonomagma- tic activation Orogene Island arc Spreading zone Tectonomag- matic Orogene Tcctonomagma- tic activation (?) Spreading zone 9 Dcvonian 7 Sudete ? < l Rifcan Laramian Prebaikalian Paleokimmerian Paleozoic Apuseni Mts North Danubian 4. North Dobrogea vrogenc provincc 5. Gabbro peridoti-j tic complexes Balkan provincc 1 Institutul Geological României L'- Conlinues in Yugo- slavia (Bor, Maij- danpek etc.) Hun gary = Basites with sulphides (Highiș) Vanadiferous titanomag- nelite (Ciungani) Sulphides (Pb-Zn) Vorța?; sulphides (Cn), Valea Lun- gă?; Ciungani Mn-l'e (Troaș-Pirnești) Mn (Pădurea Turzii, Buru) Fe, Mo, Cu, Pb-Zn (Ocna de Fier, Dognecea, Ora- vița, Șasea Montană, Mol- dova Nouă) Pb-Zn (Cu), Poiana Ruscă Cu-Mo-Bi (Băi(a), Fe (Bă- ișoara) and Cu-Pb-Zn (Vlă- deasa) Complex sulphides depo- sits Complex sulphides depo- sits Au(Oaș-Baia Marc), Hg in Soviet Union Sulphides (Pb-Zn±Cu), Toroiaga, Țibleș, Rodna; Hg-Sintimbru (Har- ghita); S-Ncgoiul Româ- nesc (Căliman) Volcanites with sulphi- des (Birgău), magmati- tes (Ciceu, Dej) and zeo- litic volcanic tuffs ie Hydrothermal Orthomagmatic Hydrothermal Volcanogenc-scdi- mcntary ” (?) Hydrothermal skarn > » »» Hydrothermal Hydrothermal (lo- eally skarn) -r Subduction zone - * * Spreading zone (island arc) »> Ci Paleoalpine (Ta-V-Q ,» >> Laramian Neogene >» >» Ol Higliiș Drocea-Mureș Trascău Banat Poiana Ruscă Apuseni Mts BOrzsony Zemplăny Vihorlat-Gutin Toroiaga-Căli- man-Harghita 6. Metallogenetic provincc associated with the ophiolitic magmatism from the Apuseni Mts 7. Metallogenetic provincc associa- ted with the bana- titic magmatism (Laramian) 8. Metallogenetic provincc of the Car pathian Neocrup- tive Chain Institutul Geological României Institutul Geological României 192 I. MIRZA 8 Institutul Geological României 9 TECTOSTRUCTURAL FACTOR . METALLOGENETIC PROVINCES 193 Fig. — Endogene metallogenetic (petrometallogenetic) provinces on the S. R. Romania territory, as compared to structural units. 1, East European Platform province, at the Moldavian Platform sub-province ; 2, Moesian Platform province ; 2 a, Wallachian sub-province ; 2 b, South Dobrogea sub-province ; 2 c, Central Dobrogea sub-province ; 3, Carpathian Crystalline pro- vince ; 3 a, East Carpathians sub-province ; 3 b, South Carpathians sub-province ; 3 c, Apuseni Mts sub-province; 4, North Dobrogea Orogene province ; 5, Balkan province of gabbro-peridotitic complexes ; 5 a, North Danubian sub-province of Paleozoic ultrabasic magmatites ; 6, metallogenetic province associated with the Mesozoic ophiolitic magmatism of the Apuseni Mts ; 6 a, Highiș sub-province ; 6 b, Drocea-Mureș sub-province ; 6 c, Trascău sub-province ; 7, metallogenetic province associated with the banatitic magmatism (Laramian) : 7 a, Apuseni Mts sub-province; 7 b, Poiana Rusca sub-province ; 7 c, Banat sub-province ; 8, metallogenetic province of the Carphathian neoeruptive chain ; 8 a, Borzsbny- Zempleny sub-province (in Hungary, continued on the Soviet Union territory) ; 8 b, Vihorlat-Gutin sub-province; 8 c, Toroiaga-Căliman-Harghita sub-province; 9, metallogenetic province associated with neomagmatism in the Apuseni Mts. REFERENCES Bilibin I. A. (1955) Metallogeneticeskie provinții i metallogeniceskie epohi. Gos- geoltehizdat, Moskow. Bleahu M., Boccaletti M., Manetti P., Peltz S. (1973) The Carpatian Arc, A Con- tinental Arc Displaying the Features of An ’Tsland Arc“. J. Geophys. Res., 78, 23, 5025—5032. Blondei F. (1938) La repartition regionale des gisements mineraux. Bull. Soc. Geol. Fr. (5), 8, 147—160, Paris. Closets F. de (1972) La derive des gisements. Sci. Avenir, 300. Codarcea-Dessila M. (1968) Considerații asupra etapelor metalogenetice prealpine din Carpații Orientali. St. cerc, geol., geofiz. geogr., Geol., 13 2, 423—430, București. Dimitrescu R. (1961) Provincii și epoci metalogenetice în R.P.R. Rev. minelor, XII 6, 258—262, București. Emmons S. F. (1913) Ore Deposits. Am. Inst. Min., 5, New York. lanovici V., Rădulescu D., Dimitrescu R., Krautner H., Mirăuță O. (1966) La carte metallogenique de la Roumănie, echelle 1 :2 500 000. Rev. roum. geol., geophys. geogr., Geol., 10 2, 149—160, București. Jankovic S. (1967) Metalogenetske epohe i rudonosna podrucja Jugoslavia, Beograd. Edit. Rudarsko-geoloski fakultet u Beogradu i Rudarski institut Beograd (Zemun). I.aunay de L. (1913) Trăite de metallogenie. Gîtes mineraux et metalliferes. Edit. Ch. Beranger, Paris. Lucea V. (1967) Le magmatisme et la metallogenie du territoire de la Roumănie. St. Vniv. „Babeș-Bolyai“, Geol.-Geogr., 1, 7—15, Cluj. • Magakian I. G. (1967) Tipî rudnîh provinții i rudnîh formații S.S.S.R. Zap. Vs. Mineral. Obșc., II, 5, 557—583. Mârza I. (1982) Geneza zăcămintelor de origine magmatică. I. Edit. Dacia, Cluj- Napoca. Noble J. A. (1970) Metal Provinces of the Western United States. Bull. Geol. Soc. Am., 81, 1607—1624. 13- c. 667 Institutul Geological României 194 I. MlRZA 10 Petraschek W. E. (1965) Typical Features of Metallogenic Provinces. Econ. Geol., 60, 8, 1620—1634. Rădulescu D. (1966) Einige Bemerkungen iiber den Begriff „metallogenetische Provinz". Mineral. Bag. Forsch., 4, 11. Rădulescu D., Săndulescu M. (1973) The Plate-tectonics Concept and the Geolo- gica! Structure of the Carpathians. Tectonophysics, 19, 3, 155—228, Amsterdam. Routhier P. (1963) Les gisements metalliferes Ed. Masson et Cie, Paris. Sillitoe R. H. (1972) Relation of Metal Provinces in Western America to Sub- duction of Oceanic Litosphere. Geol. Soc. Am. Bull., 83, 813—818. Smirnov V. I. (1959) Essais de subdivision metallogenique du territoire de l’U.R.S.S. Bull. Soc. Geol. Fr. (7), 1, 5, 511—526, Paris. Socolescu M. (1961) Observații asupra metalogenezei și zonalității în provinciile metalogenetice ale Carpaților Orientali și Baia Mare. Rev. minelor, XII/1, 30—37, București. Stanciu V. (1930) Provinciile minerale ale României. Rev. Muz. min. Univ. Cluj, III, 2, 1—32, Cluj. Șceglov A. D. (1979) Fundamentals of Metallogenic Analysis. MIR, Moscow. Tatarinov P. M. (1967) Condițiile de formare a zăcămintelor de minereuri metali- fere și nemetalifere. Edit. tehnică, București. Turneaure F. S. (1955) Metallogenic Provinces and Epochs. Econ. Geol., 50, 38—98. 4 JA Institutul Geological României \ IGRZ Gisements GEOLOGY OF THE MAIN COAL BASINS IN ROMANIA BY SERGIU NĂSTĂSEANU1 In the Romanian territory, in the Hercynian and Alpine structural setting, there are coal basins of geosynclinal, intermediate, inter- and intramountainous types. The size of deposits and the quality of coal have been determined by the different geological conditions under which developed the humito-genetic provinces that succeeded during five time intervals : Upper Carboniferous, Lower Jurassic, Upper Cre- taceous, Oligocene-Lower Miocene and Middle Miocene-Lower Pleisto- cene (PI.). One notes the following petrographic types of coal : anthra- cite. bituminous coal, subbituminous coal f’Hartbraunkohle") and lignite (”Weichbraunkohle“). Geosynclinal Basins In different geosynclinal units belonging to the Southern segment of the Carpathian Orogen, accumulated coal deposits preserved in five basins (PI.) as follows : Reșița (1), S ir inia (2), Mehedinți (3), Codlea- Vulcan (4) and Rusca Montană (5). These basins have been extensively investigated (Antonescu, Năstăseanu, 1977 ; Bițoianu, 1973 ; Năstăseanu, 1964. 1978, 1979 ; Năstăseanu et al., 1973, 1981 ; Răileanu, 1953 ; Semaka, 1970, etc.) and it has been concluded that only the first two ones are more important. Reșița Basin Inside the South Carpathians there are partly superposed coal basins located in the basement of the Hercynian molasse Westphalian- Autunian) and in the Early Lower Jurassic deposits. W estphalian-Autunian The Hercynian molasse consists of continental-lacustrian deposits (2000—2500 m thick) and lies unconformably over the pre-Sudetian metamorphic formations. It is partly detached off the metamorphic basement and involved, from west eastwards, in some overthrust units : Reșița (upper unit), Dealu Vremii, Lupac and Semenic (lower unit). The molasse deposits of the first three units include several dis- tinct conformable lithostratigraphic members. The Doman Beds consist of breecias which contain coarse-grained cobbles of crystalline rocks and are probably of Westphalian C age. They 1 Institute of Geology and Geophysics. str. Caransebeș 1, 78344 Bucharest. 196 S. NASTASEANU 2 represent the base of the molasse deposits in the Reșița (Fig. 1 a) and Lupac (Fig. 1 b) units. Fig. 1. — Correlation of coal-bearing formations in the Reșița and Sirinia basins. 1, breccias ; 2, conglomerates ; 3, sandstones ; 4, siltites ; 5, clays ; 6, bituminous clays ; 7, refractory clays ; 8, marly limestones ; 9, limestones ; 10, coal ; 11. volcano-detrital rocks; 12, rhyolites and ignimbrites ; 13, basalts and andesites; 14, metamorphic rocks : 15, overthrust plane ; 16, geological boundary ; 17, unconformity. Institutul Geological României 3 GEOLOGY OF THE MAIN COAL DEPOSITS IN ROMANIA 197 The Lupacu Bătrîn Beds are mainly of sandy-conglomerate na- ture and consist of at least four energetic bituminous coal layers, 0.30—3 m thick, in the Lupac Unit (Fig. 1 b), as well as of unimportant lenses in the Reșița Unit (Fig. 1 a). The paleoflora association (Neurop- teris gigantea, N. ovata, Pecopteris feminaeformis, etc.) reported from both units points to the Westphalian D and Stephanian A—B ages of these beds. The Lupac Beds consist of black siltites with frequent ferruginous spherolites and include three energetic bituminous coal layers. 0.30— 8 m thick, also reported from the Lupac Unit (Fig. 1 b). The abundant fossil flora (Annularia stelata, Calamites suckowi, Pecopteris arborescens, Sphenophyllum longifolium, etc.) accounts for the Stephanian C—D age. The black shales horizon contains usually Walchia and Callipteris conferta remains, species of Florinites and Potoneisporites genera, macro- and microflora typical of the Autunian. The sandy-conglomerate complex, with shales and red siltite in- terlayerings, occurs at the top of the molasse deposits. It includes the same macro- and microflora associations as the preceding horizon. As regards the Semenic Unit, the lithostratigraphic members men- tioned above are no longer recognized, while the conformity of the molasse deposits is interrupted by a sedimentation gap corresponding to the Stephanian B—D. In the abandoned deposit at Secu (Fig. 1 c) were exploited four layers of coking bituminous coal, 0.30—2 m thick, belonging to Westphalian D and Stephanian A. The coal layers overlie Lower Westphalian deposits 250 m thick. At Secu, the metamorphic rocks of the coal layers are unconformably overlain by the red sandy- conglomerate complex which contains Walchia and Callipteris conferta, typical of the Autunian. Lower Jurassic The Lower Jurassic rocks (300—450 m) overlie unconformably the Hercynian molasse and the metamorphic formations of the Semenic Unit. The Hettangian (ht) and the Sinemurian (si) are represented by a psammo-psephitic complex with rare interlayered refractory clays, clays, coaly shales and coal layers. The Anina deposit (Fig. 1 d) consists of eight layers of coking bituminous coal, while the abandoned Doman deposit (Fig'. 1 e) contained only three energetic bituminous coal layers ; the thickness of the layers varies between 0.30—3 m. The macro- and microflora associations (Pterophyllum rigidum, Podozamites mucronatus, Aletopteris dentata, Nilssonia orientalis, Chasmatosporites major, Mono- sulcites minimus, Cerebropollenites mesozoicum, etc.) point to the age of the coal complex. The Pliensbachian (pl) and the Toarcian (tc) are represented by a complex of argillaceous oii shales with thin sferosiderite interlayer- ings and coal lenses ini places. The age of the oii shales has been stated based on a rich palynological association (Auritulinosporites scanicus, Todisporites major, Foraminisporites jurassicus, Cyathidites australis, etc) as well as on ammonite remnants (Grammoceras fallaciosum). Aale- nian (aa)-Lower Callovian (cl i) marly limestones occur conformably. Institutul Geological României 198 S. NASTASEANU -I The coal-bearing formations in the Reșița Basin are characterized by complex structure, as a result of several tectogenetic phases, out of which the Laramian one was the most important ; it is then that the nappes were emplaced and numerous N—S or NNE—SSW tiending reverse faults were formed. Post-Laramian tectonica is mainly charac- terized by vertical and/or subvertical faults. Sirinia Basin Outward the South Carpathians, overlying the Inner Danubian Unit, there are the same coal-bearing formations, characterized by slightly different lithofacies as compared to those typical of the Reșița Basin. W estphalian-Autunian The Hercynian molasse (2000—2500 m) consists of two superposed rock complexes delimited by an unconformity : a lower discontinuous terrigenous complex underlying an upper volcano-sedimentary complex. The terrigenous complex overlies unconformably the pre-Sudetian metamorphic formations. It is built up of conglomerates, sandstones, siltites, coal shales and coal (energetic bituminous coal). To sedimentary rocks igneous rocks (basalts and andesites) associate in places. At Baia Nouă (Fig. 1 f), in a small tectonized syncline, was mined a coal layer (1—40 m thick) at the base of the terrigenous complex and directly overlain by Autunian rhyolites. The paleoflora association (Neuropteris gigantea, Mariopteris sauveuri, Sphenophyllum cuneifolium, etc.) points to the Westphalian C and D age of the coal layers in the Baia Nouă exhausted deposit. In the Camenița (Fig. 1 g) and Dragosela (Fig. 1 h) valleys there is another lens-like coal layer (0.30—3 m thick), located at the top of the complex and including a macroflora association, similar to that one reported from Secu, typical of Westphalian D and Stephanian A. The volcano-sedimentary complex exhibits varied lithological features : it consists, at the base, of conglomerates and sandstones with siltite and red clay interbeddings and fresh water limestone lenses in places ; in the middle, terrigenous rocks are less numerous and soon replaced by igneous rocks (tuffs and agglomerates), while at the top, there are ignimbrite and rhyolite flows. Isolated flora debris (Walchia) point to the Autunian age of this complex. Lower Jurassic Older formations are unconformably overlain by Lower Jurassic formations represented by two facies : a well represented detrital facies and a partly carbonate facies, more limited and deprived of coal. The detrital facies (500—700 m) includes three lithostratigraphic complexes assigned to Hettangian-Sinemurian, Pliensbachian and Toarcian. 5 GEOLOGY OF THE MAIN COAL DEPOSITS IN ROMANIA 199 The Hettangian and the Sinemurian consist of sandy-conglomerates coarse grained at the base and fine grained at the top, with frequent interbedded coal shales and coal layers. The Cozla deposit (Fig. 1 i) includes three layers of coking bitu- minous coal, 0.30—5 m thiek, while the Bigăr deposit (Fig. 1 j) includes five layers of energetic bituminous coal, 0.30—2 m thiek. The age of these coal deposits has been stated according to the paleoflora associations similar to the ones reported from the Reșița Basin. The Pliensbachian is represented main'ly by argillaceous-siltic rocks which include marine fauna (Gryphaea cymbrium, Aequipecten aequi- valvis, etc.). The Toarcian is sandy at the base (Lespezi Beds) including am- monites (Dactylioceras semicelatwm) and argillaceous-siltic at the top (Zamonița Beds). It is conformably overlain by sandy rocks (Moșnic Beds) of Aalenian age. Its structure Consolidated during the same main tectogenetic phases (Pfaltzic, Austrian and Laramian) as the Reșița Basin. This is characte- rized by numerous reverse faults, along which the western compartments overthrust the eastern ones. The coal deposits are also affected by post- Laramian vertical and/or sub-vertical faults. Intermediate Basins Outward the Carpathian Orogen (PI.) it is to note the Dacic (6) and Moldavian (7) basins. Their basements include both outer orogen units and inner sectors of neighbouring platforms (Moesian, Scythian, East European). The Neogene formations in these basins include lignite deposits, but only the Dacic Basin is worth studying. Dacic Basin The area bordered by the Carpathians, the Balkans and the Măcin Mts is the Neogene sedimentation area of the Dacic Basin. There are numerous studies regarding this basin, but in view of a concise account only syntheses have been used (Andreescu, 1972 ; Marinescu et al., 1981 ; Motaș et al., 1974 ; Pană et al., 1981, etc.). The Neogene molasse (5000—15000 m) consists of marine deposits with evaporites, at the base, and limnic deposits with coal, at the top. In the Romanian territory this basin covers two major units : 1. the Carpathian Foredeep, including the Wallachian Subunit, between Trotuș and Argeșel valleys, and the Getic Subunit, west of Argeșel Valley ; 2. the Moesian Platform, including the northern Danubian sector and the Southern Dobrogea. The coal-bearing formations are of Meotian, Pontian, Dacian, Ro- manian and Lower Pleistocene age. They show great lithofacies varia- tions, depending on the underlying tectonic unit. The thickness of coal deposits is reduced (200—500 m) in the Moesian Platform and increases Institutul Geological României 200 S. NASTASEANU fi gradually, from south northwards, to thousands of meters (5000— 8000 m) in some areas of the foredeep. The Meotian starts with marls or- sandstones including Congeria, Psilunio, Teodoxus, etc., then a Dosinia layer overlain by sands con- Fig. 2. — Correlation of coal-bearing formations in the Dacic Basin. 1, gravels ; 2, sands and sandstones ; 3, sandy clays ; 4. marls. taining different species of the genera Psilunio and Congeria. In the Trotuș, Valley Basin (Fig. 2 a) the Meotian rocks contain unimportant coal lenses. . The Pontian'is mainly represented by marls abunding-in limno- cardiid, dreissenid. and viviparid faunas which- point to the Odessian, Institutul Geological României 1 GEOLOGY OF THE MAIN COAL DEPOSITS IN ROMANȚA 201 Portaferrian and Bosphorian. The Pontian formations include several thin and lens-iike coal layers ; 1—3 interlayerings, 0.10—2-m thick, have been reported at Rîmnicul Sărat (Fig. 2 b), Valea Dîmbovița-Valea Argeșel (Fig. 2 e) in the Wallachian Subunit and at Schitu Golești (Fig. 2 d) in the Getic Unit. The Dacian consists of mainly sandy rocks abunding in mollusca (lymnocardiids, dreissenids, unionids, viviparids, etc.). Its base (Getian) is defined by the Pachydacna beds, while its top (Parscovian) is represen- ted by the Psilo don beds. The Romanian is represented by clays, sands and gravels. Its base (Siensian) includes the beds with Unio sturdzaie, Potomida saratae and Viviparus bifarcinatus ; the middle part abunds in sculpted unionid genera and subgenera (Rugunio, Rytia, Cuneopsidea, Pristinunio, Psilu- nio, etc.), while its top is represented by the Cîndești Beds (gravels) also present at the Lower Pleistocene level. The Dacian and Romanian formations include ca 21 coal layers, 0.10—9 m thick, the most important belonging to the Parscovian (layers IV—VII) and the Siensian (layers VIII—X) of the Getic Subunit (e.g. Motru, Fig. 2 e ; Rovinari, Fig. 2 f). In the Wallachian Subunit, the coal layers abund in places, less than 0.50 m thick (e.g. Rîmnicu Sărat, Fig. 2 b), or are rather scarce, 0.50—1.50 m thick (e.g. Valea Dîmbovița- Valea Argeșel, Fig. 2 c). On the Moesian Platform the coal layers are few, 0.10—3 m thick and occur mainly in the Dacian formations. The coal deposits in the Wallachian Subunit are obviously influ- enced by salt tectonics. Salt pierces the whole cover of Neogene rocks, in places, and generates diapir folds including almost vertical coal layers. These folds are normalized westwards, in the Getic Subunit. exhibiting slightly dipping flanks, or disappear completely in the Moe- sian Platform, where the Dacian formations include two big elevation areas and two sinking areas due to the positive and negative movements of the pre-Neogene tectonic compartments. Inter- and Intramountainous Basins The post-Laramian tectonic depressions which divided the Car- pathian belt included several basins (Pi.) : Pannonian (8), Petroșani (9), Almaș-Agrij (10). Transylvanian (11), Hațeg (12), Țara Birsei (13), Borsec-Bilbor (14) and Comănești (15) basins. The first two are most important and will be described in the following lir.es by considering the latest studies (Marinescu et al.. 1981 ; Moisescu et al., 1979). Pannonian Basin The Pannonian Basin is located among the Carpathians, the Alps and the Dinarids and only a reduced area lies in the Romanian ter- ritory. The coal-bearing formations are Badenian. Sarmatian, Pannonian s. str. and Pontian in age. Their thickness is of 2000—2500 m in the lowered tectonic compartment and much less in the elevated ones. Institutul Geological României 202 s. nastAseanu 8 The Badenian starts with coarse-grained continental formations (breccias, gravdls, sands) ; then follows a paralic facies (marls, clays, limestones, tuffites) which abunds in fossil specimens (Pycnodonta, Corbula, Cardita, Arca, Cyprinide, etc.). Extended coal interlayerings characterize the Langhian, such as : the Țebea-Brad deposit includes three subbituminous coal layers, 0.20—3.60 m thick ; the Bozovici de- posit consists of 11 layers, 0.20—3 m thick and the Caransebeș deposit (Fig. 3 a) contains three Jignite layers, 1—4 m thick. The Sarmatian is frequently represented by detrital and carbonate rocks, rich in fossils (Ervilia, Abra, Pirenella, etc.), as well as a clayey- marly facies with coal, such as in the Borod gulf. The Borod deposit (Fig. 3 b) consists of two lens-like lignite interlayerings, 1—2 m thick. The Pannonian s. str. (Malvensian) consists of clayey-sandy rocks with fossils (Origoceras fuchsi, Congeria banatica, etc.), is well deve- loped all over the basin and includes only minor lignite lenses. The Pontian formation stands out as the most important as re- gards both its great thickness (100—1500 m) and the large number of lignite interlayerings, belonging to the Portaferrian especially. It con- sists of gravels, sands (bituminous in places), sandstones, tuffites and clays abunding in congerias, lymnocardiids and ostracods. The best known coal accumulations occur in the following regions : Șimleu Sil- vaniei (Fig. 3 c), containing 27 coal layers, out of which 19 are 0.50— 3 m thick ; Beiuș, containing two lens-like layers, 1.5—2.50 m thick ; and Lugoj (Fig. 3 d), with ten layers, 0.50—3.60 m thick. The coal deposits exhibit a simple structure, the Neogene rocks forming slightly dipping wide anticlines and synclines. Petroșani Basin This basin lies in the South Carpathians and consists of molasse deposits in continental-lacustrian facies, accumulated during the Oligo- cene-Lower Miocene interval. It contains the most important bituminous coal (partly coking) deposits in the country. The coal-bearing formations are 1800—2000 m thick and belong to the Chattian and Aquitanian which succeed conformably (Fig. 3 e). The Chattian consists of : 1) basal conglomerate horizon, unconfor- mably overlying the older formations ; 2) middle sandy-argillaceous horizon, including 18—21 coal layers, 0.50—30 m thick, characterized by a rich paleontological content (Corbula giba, C. carinata, Gobraeus protractus, Glyptostrobus europaeus, etc.) and 3) upper sandy horizon deprived of coal. The Aquitanian is represented by a lower argillaceous-sandy hori- zon including Crassostrea, Tellina, Mytilus aquitanicus, etc., with five to eight lens-like coal layers, 0.20—0.80 m thick, and an upper sandy horizon with marine fauna (Chlamys gigas, etc.). The Petroșani deposit exhibits a simple structure, characterized by several ENE—WSW trending anticlines and synclines, affected by vertical or subvertical faults. Institutul Geological României 9 GEOLOGY OF THE MAI'N COAL DEPOSITS IN ROMANIA 203 Fig. 3. — Correlation of coal-bearing formations in the Pannonian Basin and synthetic lithostratigraphic column of the Petroșani deposits. 1, oii shales ; 2, tuffite ; 3, gypsum. REFERENCES Andreescu I. (1972) Contribution â l’etude du Dacien et du Romanien de la zone de courbure des Carpates Orientales. D. S. Inst. geol., 58/4 (1971), 131—151, București. Institutul Geological României 204 S. NASTASEANU 10 Antonescu E., Năstăseanu S. (1977) Contributions palynologiques ă la connaissance du Permien du Banat. D. S. Inst. geol. geofiz., LXIII, 1976. 73—1)4, București. Bițoianu C. (1973) La flore du Carbonifere superieur de la Roumănie. C. R., 2, 115—127, 7 I.K.K., Krefeld. Marinescu F., Ghenea C., Papai'anopol I. (1981) Stratigraphy of the Neogene and the Pleistocene Boundary. Guidebook to Excursion A 6, 12th Congr. Carp.- Balk. Geol. Assoc., Bucharest. Moisescu V., Chivu M., Dragu V., Mărgărit E. (1979) Studiul faunei de moluște egeriene din bazinul Petroșani. Mem. Inst. geol. geofiz., XXIX, București. Năstăseanu S. (1964) Prezentarea hărții geologice a zonei Reșița-Moldova Nouă. An. Corn. Geol., 49 1 (1962), 291—342, București. — (1978) Considerations preliminaires sur l’existence d’un systeme de nappes alpines dans la zone de Reșița ă Lupac (Banat). D. S. Inst. geol. geofiz., LXIV (1977), 89—106, București. — (1979) Les formations sedimentai,res paleozoîque superieures et mesozoîques du Banat. Rev. roum. geol., geophys. geogr., Geol., 23/2, 159—166, București. — Stănoiu I., Bițoianu C. (1973) Corelarea formațiunilor hercinice (Westphalian • Permian) din partea vestică a Carpaților Meridionali. An. Inst. geol., LX (1971), 71—109, București. — Bercia L, lancu V., Vlad S., Hârtopanu I (1981) The Structure of the South Carpathians (Mehedinți-Banat Area). Guidebook to Excursion B 2, 12th Congr. Carp.-Balk. Geol. Assoc., Bucharest. Pană L, Enache C., Andreescu I. (1981) Fauna de moluște a depozitelor cu ligniți din Oltenia. I. P. „Oltenia", 275 p., Craiova. Răileanu Gr. (1953) Cercetări geologice în regiunea Svinița-Fața Mare. Acad. R.P.R., Bul. șt. Secț. biol., agron., geol., geogr., 5/2, 307—409, București. Semaka Al. (1970) Geologisch-Paladbotanische Untersuchungen im SO-Banater Danubicum. Mem. Inst. geol., 11, 79, București. S- NĂSTĂSEANU- Gcology of thc Main Coal Deposits Romania Imprim. Atei.Inst.Geol.Ge of ANUARUL INSTITUTULUI DE GEOLOGIE £1 GEOFIZICĂ. VOI LXIV m s ti t ut-u-l-&^o log te- a l-Româm-e-4 igrZ Gisements THE EVOLUTION OF THE HYDROCARBON FIELD DISTRIBUTION IN THE MOESIAN PLATFORM BY DUMITRU PARASCHIV 1 Stratigraphically, the Moesian Platform basement, Consolidated at the end of Proterozoic, underlies a more or less complete sedimentary sequence, the age of which ranges from the Cambrian (?) to the Quater- nary. The sedimentary cover of the platform may reach thicknesses of 10 000 m, consisting of an alternation of terrigenous and carbonatic for- mations, most of them of marine origin. The prospection and exploration activity, performed up to now within the platform, allowed the discovery of about 140 oii and gas structures. Hydrocarbons are stored in the Devonian, Permo-Triassic, Dogger, Malm-Lower Cretaceous, Senonian, Badenian-Sarmatian, Meo- tian, Pontian and even Dacian formations. The major idea which backed this hydrocarbon prospection and exploration activity was that the Moesian Domain represents a quiet and almost continuous accumulating area, beginning with the Cam- brian. The sedimentary character changed over long periods, namely the large alternance of terrigenous and carbonatic sequences, the for- mation or reactivation of some ruptural accidents and the gradual fading of the positive and negative forms inherited from the basement level, were the main events which occurred in the quiet and unitary evolution of this domain. The geological and geophysical data gathered during a first stage of researches pointed out a pattern according to which the general sedimentary deposit arrangement is of a faulted monocline falling in steps in front of the Carpathians. Some geologists have extended this image to the whole sedimentary sequence, while others have fully accepted it, at least from the Jurassic. As far as the hydrocarbon pool formation and distribution is concerned, it was gene- rally (Paraschiv, 1979) and even exclusively (Pătruț et al., 1983) agreed that the oii and gas were generated and entraped during the Sarmatian- ’ Research and Designing Institute for Oii and Gas, str. Toamnei 103, Bucharest. ■A Institutul Geologic al României \ IGRZ 205 D. PARASCHIV Pliocene subsidence and as such the huge monocline sectioned by rup- tural accidents controlled the accumulation distribution (Fig. 1). In time, the economic potențial of this geological conception began to decrease. At the same time, a vast volume of data accumulated and, together with the progress of fundamental researches and the ”noncon- formist” distribution of some pools, made possible new ideas and inter- pretations, to be applied in prospection and exploration designing. Within the new conception, the history of the Moesian Platform comes out in a much more dynamic development, very complex and non-unitary. When outlining this image, some essential elements to be referred to later on, have been taken into account. As regards the profound structural aspect, the Moesian area is not a unitary one. At least two big crust segments make it up : the western ,part of the Biack Sea Microplate, between the lanca-Palazu and Belciugate faults, and the Moesian Microplate west of Belciugate Fault. Constituted in their turn of several blocks, those microplates manifested themselves through dynamical and geothermal differentiated regimes which brought about variations in the deposit thickness and the facies distribution and even in the rock diagenesis (the incorporated organic matter included). One may say that this deep structure, proper to the Moesian area, is responsible for the detail variations of the sedi- mentary cover constituion and of the diagenesis of the organic matter. The major features, very much as the whole ensemble evolution of the territory under discussion, have to be connected with the rela- tions established and which followed between the two main geodynamic factors of a total importance : the Euro-Asian continental Block — which acted from the east, and the African continental Block which acted from the south. In rhythmical expansion, those geodynamic giants exerted alternatively their influence on the area between the Carpa- thians and the Balkans. The action of the global factors determined the displaying of the sedimentary basins- the facies zones, the major struc- tural lines, the fluid dynamics and the preferențial zones of hydrocar- bon accumulations, elements which were lain perpendicularly on the pushing direction of the blocks. At the same time, the displacement of 'the respective plates started and varied connections between crust segments of all sizes took place within the Moesian area. The alternative predominance of the pressure exerted by the two big plates makes necessary the separation of several evolution periods in the Moesian Platform history, since during each stage the surfaces of oii interest were oriented and distributed in a different way. During the periods when the forces from the eastern part imposed themselves, the preferențial accumulating zones were generally oriented N—S, and when the pressure from the south was predominant, the pools aligned themselves to some E—W tendencies. Another essential element considered is that the hydrocarbon could be formed and accumulated not only during the Neogene but also during other stages of the platform history, beginning with the Paleo- zoic and up to the Pliocene. This hypothesis is backed among others also by the fach that the pools discovered on the Bulgarian territory are situated in regions in which the Neogene is absent or is very Institutul Geologic al României 'GR Institutul Geologic al României 208 D. PARASCmv -1 weakly developed. Doubtless. within each stage of evolution, fluid re- mobilizations and parțial or total pool redistributions previously formed. were produced. Owing to these reasons, the more recent evolution stages and more particularly the last one, appear more prolifical, but this fact has also to be related to the older formation phases. The actual structure dating back from the Badenian if not earlier, was completed under the pressure of forces coming from the south which started the platform underpushing process. Consequently, its northern margin sunk continually in front of the Carpathians in a iracture. Concomitantly, the sedimentation was resumed in hyper-sub- sidient regime. The Neogene deposit isopachs, the facies zones and the major strctural lines (fractures) are displayed E—W, perpendicularly on the pushing force direction. The stratigraphic terms follow from the south to the north very much as the facies evolution. As a result, the organic matter diagenesis more prominent on the sunken northern margin of the platform decreases southwards. The lateral migration sense was the same from north to south, the pools displaying on E—W oriented alignments (Fig. 1). As it will be seen later on. the Neogene evolution stage of the Moesian Platform determined the re-dynamization of the previously accumulated and formed fluids and their parțial re-distribution along the newly created structural elements east-westward. Another stage of evolution in the Moesian Platform history cor- responds to the Cretaceous and Jurassic. During this time the Euro- Asian Plate was much more active in comparison with the African one ; thus the Moesian area developed under the influence of pressures exerted from the east. The sedimentary basins, the isopachs, the facies zones, as well as the main productive alignments seem to have been oriented N—S, NW—SE or NE—SW. Possible to have been noticed from the very beginning of the Jurassic, such tendencies were locally extended up to the Eocene ; proof of it is that the Lom Basin goes on northward close to the town of Craiova, and the Varna Depression is passing beyond the parallel of the locality of Slobozia. A better studied stratigraphic sequence — seen its economic importance — is that one belonging to the Albian. On close examination of Figure 2, one can see that both the lithofacies evolution and the denu- dation were controlled by the displacement of the Euro-Asian conti- nental Block. Thus. in the western sector of the platform, pelitic pelagic deposits were accumulated ; the gritty-calcareous facies is predominant in the central sector ; while the gritty-siltic rocks are predominant in the eastern part. The denudated surfaces are also oriented N—S. Pro- bably, the hydrocarbons generated by the pelagic sequence migrated laterally in the gritty-calcareous rocks. In fact, the surface of economic interest of the Albian is related to the gritty-calcareous facies zone. In the geological context under review, it is difficult to admit that the productive alignments of the Albian were subject to other inițial tendencies than those trending N—S. It is true that some pools and, first and foremost. those on the Corbii Mari-Petrești structure appear as stretched east-westward. but they are hydrocarbons re-distributed during the Neogene ; proof of Fig. 2. — Albian lithofacies and hydrocarbon pools located in this formation. line marking the disappearance of the Albian ; 2, Upper Albian in pelagic facies ; 3, Albian in calcareous-gritly facies 4, Lower-Middle Albian in gritty-siltic facies ; 5. hydrocarbon popi; 6, pericarpathîan line. 14 — c. 6S7 Institutul Geological României 210 D. PARASCHIV it is that the above-mentioned structure is produced by the Sarmatian as well. But on other structural elements in the gritty-calcareous facies zone, hydrocarbons are to be found only in the Albian. More than that, in the Buzescu-Nenciulești sector, the unproductive Sarmatian is not involved in the tectonics proper to the Albian gas-bearing deposits. a fact suggesting that the first phase of the hydrocarbon accumulations in the respective zone took place before the Miocene, maybe, the end of the Cretaceous. Similarly, the Cretaceous deposits, older than the Albian were studied ; the same goes for those belonging to the Malm, which, togeth- er, make up a plate almost exclusively carbonatic. Figure 3 shows the Barremian-Aptian distribution and facial differentiations of these terms. The respective picture is very much similar to that of the Albian, namely N—S orientation of surfaces covered by Barremian-Aptian deposits as well as the zones affected by denudation. The western sub- basin — more developed and made up of micritic limestones — is divided by a limestone zone with intraclasts and reefs NE—SW orien- ted. The eastern sub-basin strongly fragmented by erosion is aligned NW—SE together with its appended areas. Hydrocarbon pools, obviously controlled by NW—SE tendencies in the eastern sub-basin, also under- went Neogene ”corrections“ more particularly in the Ciurești perimetre. According to the reference material (Costea et al., 1978, Vinogradov et al., 1978) the rock distribution and the facies evolution of the Lower- most Cretaceous and Malm deposits are very much alike with those of the Mesozoic stratigraphic sequences discussed before. At the level of the Jurassic terrigeneous sequence '(the Balș For- mation), the isopachs map (enclosure 4) shows the NW—SE disposition of the main lines and implicitly of the basin depocentre. Hydrocarbon pools are more often encountered on the margin of the basin, corres- ponding, however, to thicknesses over 100 m. Obviously, subject to some directions parallel to the basin’s axis (NW—SE), some of the pools (Ciurești, Oporelu) also bear the mark of the Neogene re-dynamîzation. The elements under discussion may state that most of the pools located in the Cretaceous (Senonian. Albian, Neocomian) and Jurassic (Malm, Dogger) are displayed along some zones or alignments oriented N—S, NW—SE or NE—SW in accordance with the sedimentary basin dynamics of the respective periods. One can also see some exceptions, namely E—W orientations suggesting older accumulation re-distribution during the Neogene. There are also some other discrepancies, such as subtle traps (lithological variations of porosity and permiability). The Eokimmerian diastrophism marks .an important change in the evolution of the Moesian Platform, namely posterioi’ to the respective event, the area under discussion developed unitarily, while prior to the Jurassic, the eastern sector (the Black Sea Plate) continually under- went the influences of the Euro-Asian continental Block ; the western sector (the Moesian Microplate) being alternatively subject to the pres- sure of the two plates. In fact, productive formations older than the Jurassic, i.e. Triassic and Devonian, are known up to now only west of Bucharest meridian. Institutul Geologic al României 7 HYDROCARBON FIELD DISTRIBUTION- MOESIAN PLATFORM 211 Institutul Geological României 212 D. PARASCHIV "8 Fig. 4 — Isopach map of the Balș Formation and its hydrocarbon pools. line marking the Balș Formation disappearance ; 2, isopachs ; 3, hydrocarbon pool ; 4, pericarpathian line. Institutul Geological României 9 HYDROCARBON FIELD DISTRIBUTION-MOESIAN PLATFORM 213 The Triassic deposit distribution, the evolution of these facies and a number of ,plicative structural elements (E—W oriented) seem to point out that the western half of the Moesian Platform was subject to pres- sures coming from the south. The hydrocarbon pools, however, have a -chaotic spreading. This is probably due to the fluid re-dynamizations and re-distributions, following the Triassic. As a matter of fact, most of the accumulations located in the Triassic form common hydrody- namic units with those in the Dogger. On the other hand, the study of the lithostratigraphical terms of the Triassic is still unsufficient and a further action will bring out additional data useful in this respect. However, it is to be expected that the “sealed” pools of the Triassic will follow the E—W tendency. Only one productive structure was discovered in the Devonian, therefore the reconstruction of the old tendencies cannot benefit by the necessary fundamental elements. One may say, however, that both the Devonian and the Triassic belong to some stages of different evolution. Besides geological arguments, it is to be stressed that the curve indi- cating the degree of the organic matter transformation shows an impor- tant threshold and gradient change at the boundary between the Permo-Triassic and the Devonian. This implies notable changes in the geodynamic and geothermal regime of the platform at the respective moment. The distribution of the hydrocarbon pools seems to be more and more difficult to decipher starting from the present situation to the past. Nevertheless, some tendencies in their distributions are forsee- able. It is, however, a fact that the zones and the preferențial accumu- lation alignments have undergone particular changes in the geological past and that the conception regarding their prospection and explora- tion has to take into account such situations. REFERENCES Costea I., Comșa D., Vinogradov C. (1978) Microfaciesurile Cretacicului inferior din platforma moesică. St. cerc, geol., geofiz., geogr., Geol., 23/2, 299—311, București. Paraschiv D. (1979) Platforma moesică și zăcămintele ei de hidrocarburi, Edit. Acad. R.S.R., 195 p., București. Pătruț I., Butac Al., Balteș N. (1983) Main Stages of Hydrocarbon Generation and Accumulation on the Romanian Territory of the Moesian Platform. An. Inst. geol., geofiz., LX (Trav. XII-e Congr. Assoc, Geol. Carp-Balk.), 315—323, București. Vinogradov C., Costea I., Comșa D. (1978) Microfaciesuri jurasice superioare din platforma moesică corelate cu depozite sincrone din zone învecinate. St. cerc, geol., geofiz., geogr., Geol., 23/1, 65—72, București. Institutul Geological României Institutul Geologic al României Gisements ON THE NATURAL DEGASIFICATION OF THE HYDROCARBON- BEARING DEPOSITS IN ROMANIA BY DUMITRU PARASCHIV1 The detailed geological mapping (sc. 1 : 25.000) performed in all sedimentary basins of Romania has led to the Identification of about 1.000 points with oii and gas natural seepages associated with formation waters, H2S, CO2, N2, etc. (Tonescu, 1953). This large number of occur- rences is on the one hand an indication of the petrologenous and petro- liferous potențial of the respective sedimentary basins, and on the other hand an image of the proportions and stage reached by the natural depletion process of pools. The recently drawn synthesis map (PI. I) shows that hydrocarbon occurrence distribution at the surface is ununiform, both spatially and in point of rock age, where they are to be found. First and foremost, it would be worth stressing that out of the total of 1,000 points with seepages, 73% represent oii springs associated •or not with gas or formation water, and only 27% are gas emanations, mud volcanoes included. Most of the gas occurrences are grouped in the Neogene basin of Transylvania, proved up to now to be exclusive gas- bearing, as well as in the Getic Depression, together with the Pliocene zone of the Carpathian Bend. This means that the gas seepages are -associated — with small exceptions — to the deposits of Sarmatian- Pliocene age, more rarely Badenian, while the oii is present in zones where deposits older than the Sarmatian or Badenian, crop out. This remark is apt to bring under discussion the stage of the organic matter diagenesis and hydrocarbon forming, namely that the oii window begins as a rule from the basis of the Sarmatian-Pliocene or even of the Badenian downwards. In other words, both in the Carpathian Flysch and Foredeep, in the internai depressions, the Lower Miocene, Paleogene and Cretaceous deposits have reached the maturation corresponding to the oii generation. The above-mentioned remark comes to prove generally the geo- chemical, biostratigraphic and petrographic investigation results, but to 1 Research and Designing Institute for Oii and Gas, str. Toamnei 103, Bucharest. 216 D. PARASCHIV a certain extent, in disagreement with the hydrocarbon physical state of the undepleted pools, discovered at depth in the afore-mentioned formations. It refers to the fact that in the pre-Badenian reservoirs, there are also free gas aceumulations, but particularly associated gas (gas cap). Under these circumstances, the gaseous hydrocarbon penury at surface would be also explained by the advanced stage of the podi depletion in the sense that the gas diffusion phase is almost consumed, the large majority of the aceumulations being in the advanced depletion stage, namely the oii leakage or oxidation and even the associated water drainage. In accordance with what we stated above, it might be admitted. that a first major remark, allowed by the analysis of the hydrocarbon occurrences at surface, is the hydrocarbon generating potențial and the physical state belonging to some formations, as well as to the pool depletion stage. This is due to the fact that the degasificaiion should not be understood and treated separately, it actually representing a first depletion stage, beginning with the gas diffusion, going on with the oii and associated water drainage, and ending with the oii reser- voir and source rock denudation. Out of the 1,000 seepages, 68% occur at the Neogene level, 26% in the Paleogene and 6° n in the Cretaceous. In the deposits older than the Cretaceous, oii springs or gas emanations were not evinced, although numerous pools were discovered at depth in such formations. This si- tuation is due to the denudation which has affected to a greater extent the deposits of recent age, upper situated, and ever less, the sedimen- tary sequences of older age. The third and the most important ascertained fact is held out by the occurrence distribution, according to the tectonic peculiarities of facial-structural units of oii interest. If out of the total number of pro- ductive structures discovered up to now (about 560), 55% belong to the Carpathian Domain and 45% to the foreland, the seepage average at surface is completely different. namely 98.5% in the folded zones and only 1.5% in the outer Carpathian zone. Therefore, within the Moesian Platform, characterized by a strong disjunctive tectonics, through the existence of about 130 pools (out of which 42 of gas) located in the Devonian-Upper Pliocene stratigraphic interval, only four hydrocarbon seepages were pointed out, and in the North-Dobrogea Promontory, where 11 pools were discovered, hydrocarbons do not occur at surface. This sharp differentiation has its origin in the tectonic movement complexity and proportion, the crust segment seismicity within the studied areas included ; these movements have led to the deformation, fragmentation, raising and then the denudation of the hydrocarbon prospective sedimentary formations. Such processes took place in the past, but they are still continuing. A proof of it is the recent crust movement map (Cornea et al., 1979). Comparing the hydrocarbon seepage distribution at surface to the neotectonic movements (PI. I), one may notice that almost all oii and gas occurrences at surface correspond to the zones affected by positive crust movements. Most of such points are registered between lines +1 and +4 mm each year, which means that the main agent of the pool depletion is the denudation. which, in Institutul Geological României IGR 3 HYDROCARBON FIELD DISTRIBUI’ION-MOESIAN PLATFORM 217 its turn, is stimulated and controlled by the crust movements. Besides, the large majority of oii springs and gas emanations occur in valleys- a fact stressing the distructive role of erosion. But within the valleys, the gravity, namely the land sliding, decurs actively enough. The refe- rence material (Tonescu, 1953) mentions numerous cases of appearance or disappearance of occurrences as a consequence of strata sliding. For instance, at Suslănești (Argeș) gas emanations due to the slope gravity processes were noticed. At Gura Drăgănesii, Păltinișu-Nehoiu and Badila, the mud volcanoes, previously known. have vanished as a result of land sliding. The depletion of oii and gas accumulations has been proved more active where the region raising was associated with the strata fractura- tion, which facilitated and accelerated the gas diffusion and oii and formation water drainage. In keeping with the mapping. more than half of hydrocarbon occurrences at surfaee lie along some disjunctive accidents. Out of them mention should be made of the oii springs and gas emanations along the tectonic line, putting into contact the flysch zone with the Miocene one (Tg. Ocna. Tg. Trotuș), of the seepages close to the Cașin-Bisoca Fault, of the accidents within the flysch zone (Slă- nic Moldova, where H>S, CO2 emanations are added) and of Zîmbroaia, Podeni, Valea Dulce, Ocnita. Lăculețe-Glodeni, Slănic-Prahova, Sările- Valea Rea, Plopeasa, Berca-Beciu-Arbănași, Govora- Măldărești, Pie- trari, Cîlnic, Aiud (in Transylvania), etc. At the same time .with the hydrocarbons, the moffete gas (CO21 N2, Ne. etc.) emanated both in the flysch zone and in the Transylvanian Depression. The plicative elements — with all their range of shapes — from domes to overlapping folds — accelerated the pool degasification. The depletion processes were more active in the case of the broken folds, namely in the circumstances of plicative and disjunctive element asso- ciations. Thus, a large number of occurrences were noticed along some anticlines, as those of Rotilești, Berca-Beciu-x\rbănași, the axis of the Homoriciu Spur (Cătiașu) and of the Văleni Spur, of Ursei (Vișinești Fault), Stîrmini, Ciocadia, Pitic, Voitești, Ruși (Transylvania), Beclean- Someș, as well as along numerous salt diapirs. as for instance : Turda, Apostolache, Vulcănești, Buștenari- Doftana, Cîmpina, Telega. Cîmpi- nița, Slătioarele, etc. The most important effects on the gas diffusion, generally, and the screen destruction, especially, seem to have been had by the seis- micity, namely the earthquakes. One may reach this conclusion by examining the oii and gas occurrence distribution map (PI. I) and the isoseismal line mao and one may find out that the maximum density of hydrocarbon seepages occurs at the Carpathian Bend (Vrancea), where the maximum seismal values (8.9) are also encountered. It would be possible that the earthquakes reactivate the fault network. cause other new disturbances, and accelerate the slope gravity processes, thus facilitating the oii and gas drainage to surfaee. One of the classical forms covered by the pool degasification in Romania is represented by mud volcanoes. Most of them were identi- fied in the Neogene Transylvanian Depression. north-west of the Getic Depression, and at the Eastern Carpathian Bend (PI. I). In Transylvania, Institutul Geological României 218 D. PARASCHIV 4 the volcanoes are to be found in the gas-bearing dome zones, subject to denudation. In the Getic Depression the respective phenomenon is usually associated to the folded anticlines. At the Carpathian Bend, the volcanism determined by the gas emanation is particularly controlled by disjunctive accidents, among which the Andreieșu and Berca-Arbă- nași faults are noticed. The crater cone, made up of the overflowed and deposited mud, all-around the occurrences, varies between some centimeters and 6—8 cm high, its maximum radius being of 25 mm (at Soroștin in Transylvania). Worth mentioning is that the quasitotal of mud volcanoes in Ro- mania cropped up on valleys within the major river beds and the river terraces. This means that the fluids (water and mud) brought about by gas, mainly come out of ground water sheets. The most intensive present-day processes of natural depletion of hydrocarbons take place, as mentioned above, at the Eastern Carpathian Bend, and, more particularly, in the Berca-Arbănași anticlinal zone (PI. II). There, the detailed maps showed a normal and continuous sequence of deposits, beginning with the Meotian, present in both axial peaks of the structure and ending with the Romanian, filling the adja- cent synclines. The Meotian is formed of mari, siltstone, sand, calca- reous sandstone and, more rarely, limestone alternation, grouped in 27 complexes cumulating 600—800 m in real thickness. The Pontian, also terrigenous, comes out somewhat more pelitic than the Meotian espe- cialiy in its third lower part. The Pontian thickness is between, 1,100— 1-500 m. The Dacian is noticed by a variation of lateral facies, some- what stronger in comparaison with that found out at the lower term level. In point of lithography, the marls, siltstones, sands and coaly schist interbeddings and coals are predominant, the respective ensemble totalling 500—600 m. The Romanian is made up of sands with clayey interbeddings or schists and coals, marls and tuffaceous sandstones, gravei, 1,500 m thick. These deposits are characterized by crossed bed- ding, more especialiy towards the upper arenitic-psephitic part of the sequence. Structurally, the Berca-Arbănași zone appears as an anticline (PI. II), 30 km in length. It is axially affected by two longitudinal faults, which, in their turn, are crossed and disconnected by other transversal disjunctive accidents. The longitudinal system of faults has a hesitant peculiarity, which determined the inversion of the rela- tions between the anticlinal flanks from one end to the other of the structure. In this way, at Arbănași, the eastern flank somewhat raised overlaps the western one, while at Berea the western flank appears higher showing a slight tendency of overlapping the eastern one. The strata dips are of 35—85° and the whole network of faults seems to be tight. The hvdrocarbon accumulations are stored in the Meotian sands. In the Southern end of the structure, gas was identified in the Sarma- tian too. The number of productive layers differs from one block to another, both on the eastern flank — more proliphic — and the western flank. The gritty reservoirs contain oii in most cases, but they are also saturated with free or associated gas. o HYDROCARBON FIELD DtSTRIBUTION-MOESIAN PLATFORM 219 The existence of numerous faults and the Meotian outcrop (or its raised position) saturated by hydrocarbons have led to the parțial and local deterioration of the protecting screens and, consequently, to the pool depletion. Therefore, in the folded axial zone of the anticline, mud volcanoes occur grouped in four sectors called ”La Fierbători", ”Pîclele Mari", ”Pîclele Mici-1 and ”Valca Arbănașului“ (PI. II). The gas emana- tions have led to the formation of some cones and craters the heights of which vary between some centimeters and 2.5 m. The gas erupts rhythmically and with variable force, entailing waters, mud, rock frag- ments and some oii. The volcanism intensity of this type increases during the rainy periods, whence the conclusion that both pool fluids and fresh waters participate in the respective process. The mud over- flows the crater cones and by drying it deposits on their flanks, which are gradually raising. The material such sedimented consists, among others, of rock fragments and even clay blocks, sandstones and gypsum, ranging in age from Burdigalian up to Pontian included (Ciocîrdel, 1959). The diversity of rocks. brought about by gas, and their ages sug- gest different relationships between the hydrocarbon source (Meotian) and the other stratigraphic terms, along the main disjunctive accidents. Generally, it may be admitted (Ciocîrdel, 1959) that gas coming from the Meotian, erodes and conveys the material from the older formation of the overthrusting raised flank. At Pîclele Mari “the block clays” overlie a surface of 1,000/600 m reaching a maximum thickness of about 20 m. The study of the existing data leads to the conclusion that the degasification and pool natural depletion processes were more intense and even more extended, not long ago. Thus, the presence of some rock blocks, in comparaison with the fine material deposited at present, suggests the substanțial diminution of the underground energy in the Berea-Arbănași sector. About 30 years ago, at Tîrcov, the mud jet raised 4 m high above the ground (Tonescu, 1953). Meantime, the eruption stopped. At Ocna Sibiului, the greatest cones in the country, 6—8 m height and 24 m radius, were identified. At present, the respective volcanoes are inactive. A similar situation was also registered at Șincai. Part of volcanoes are extinct at Soroștin, Lopatna and Bădila. At Slă- tioarele, as well as at Lopatna, the volcanoes are stieking in the mud and fossilizing the vegetation. The ”Living Fires“ or ”Unextinguished Fires“ of the Carpathian Bend, as well as the continuous gas emanations on the edge of the Lake Băicoi, used as fuel for cooking, were kept up only in the toponymy and reference materials. The natural depletion paroxysm process of the hydrocarbon pools might correspond to the latest Pliocene — early Quaternary when strong positive crust move- ments took place particularly at the Eastern Carpathian Bend (over 1,000 m high) together with a denudation recrudescence. Later on, the intensity of the respective process decreased at the same time with the diminution of the affected pool energy. Within the previously raised zones (flysch and inner flank of the Carpathian Foredeep), the depletion Institutul Geologic al României 220 D. PARASCHIV 6 is in the final stage in the sense that the erosion reached the source rock. In the latter situation, the only indices are still the hydrocarbon smeil given off by pelitic rocks (Spiratella marls, Pucioasa Beds, black schists, Sinaia Beds, etc.). REFERENCES Ciocîrdel R. (1949) Regiunea petroliferă Berca-Beciu-Arbănași. St. tehn. ee., A/4, 32 p., București. Cornea 1.. Drăgoescu I., Popescu M., Visarion M. (1979) Harta mișcărilor crustale verticale recente pe teritoriul R. S. România. St. cerc, geol., geogr., geofiz.. Geofiz., 17/1, 3—20, București. Paraschiv D. (1979) Romanian Oii and Gas Fields, St. tehn. econ., A/13, 382 p.. București. Țonescu M. (1953) Catalogul aparițiilor de țiței și gaze din R.P.R., 55 p., București. Pl.l 45km Oradea Mediaș Galați Ploiești LEGEND Bucharest seepages Mud volcanoes ANUARUL INSTITUTULUI DE GEOLOGIE Șl GEOFIZICA, VOL. LXIV -a- Pericarpathian Fault Eruptive-metamorphic rocks and other formations deprived of oii and gas prospects Isoiine of movement (mm/year) MAP OF SURFACE HYDROCARBON SEEPAGES ON THE ROMANIAN TERRITORY Institutul Geological României PI. II D PARASCHIV- Noturol Degasiftcobon oi Hydrocarbon Deposits România imprim-Atei -Inst-Geol-Geof W Geuiug ic a l' Ror^iSrHe 1 Gisements PHYSICAL-GEOLOGICAL MODELS REGARDING THE NEOERUPTIVE ROCKS IN THE BAIA MARE AREA : A CONTRIBUTION TO THE STUDY OF SOME METALLOGENETIC STRUCTURES BY MARIAN RADUȚ', SOTIRIS FOTOPOLOS 2, OSCAR EDELSTEIN 3, D1ETER HANNICH2, DUMITRU ISTVAN3, COSTEL GAȘCU3, TEODOR BÎLCU3 The Oaș-Gutîi segment of the intracarpathian chain consișt- ing of Neogene igneous rocks is characterized by a wide variety of eruptive rocks, generated during a long time interval, starting from Lower Badenian till the end of Pliocene. The volcanics belong to two formations : andesitic and rhyodacitic, with distinct features and pointing to different magma sources. The andesitic formation consists of a sequence of andesites and dacites, subaerially and subaquatically emplaced, during the Sarmatian-Plioeene interval, which form complex structures including central type volca- noes, arranged on tectono-magmatic lines with mainly mixed aetivity. The andesitic formation is built up mainly of lava flows, but also of an entire series of pyroclastic rocks, as well as subvolcanic products of intrusive processes. An ever increasing number of subvolcanic bodies has been recently pointed out, more frequently to the east. It is possible that they occur in equally great amount all over the area, but have not been. sufficiently marked, so far, below the lava flows. The sig- nifieant development of intrusive phenomena pointed to the volcano- plutonic nature of the magmatic aetivity in this area, without any available data about the occurrence of typical plutonics. The rhyodacite formation consists of tuffs, tuffites, breccias, ignimbrites and subordinately lavas, generated during two main stages : Badenian and Lower Sarmatian. As products of violent explosions, they form piles 20—200 m thick, very widespread, accurately located from stratigraphic point of view and representing real marker horizons. 1 Ministry of- Geology, str. Mendeleev 36—38, 70169 Bucharest. 2 Enterprise for Geological and Geophysical Prospection, str. Caransebeș 1, 78344 Bucharest. 3 Enterprise for Geological Prospection and Exploratioh "Maramureș-1, str. Victoriei 146, 4800 Baia Mare. Institutul Geological României 222 M. RADUȚ et al. 2 The structural images, inferred from the integrate interpretation of geological and geophysical data, prove that the magmatic activity in the Oaș-Gutîi Mts took place on a basement divided into horsts and grabens, which are built up of different rocks : the north-western area, corresponding to the Oaș Mts, which includes the western Dacides and their posttectonic cover in the basement, and the central and eastern area — the eastern Dacides and the Paleogene formations of the trans- carpathian flysch. The latter constitute nappes. This division is partly achieved along the E—W trending Bogdan Vodă fracture. The metallogenetic activity is associated with the andesitic mag- matic activity, its products occurring in sedimentary formations and igneous rocks, the latter of Badenian to Pontian age inclusively. At the spnngs of the Săpînța Valley, there is a hydrometamorphism aureole also within Upper Pliocene pyroxene andesites (Fig. 1). The mineralizations are mainly of base metal or gold-silver type and exhibit relatively varied parageneses, usually with frequent occur- rences of : galena, blende, pyrite and chalcopyrite associated with small amounts of numerous other minerals containing Pb, Zn, Cu, Ag, Fe, Au, Sb, S, etc. The gangue is represented by quartz, carbonates, clay minerals, gypsum and barytine in places. The characteristic type of ore deposit is the vein ; other types recently reported are the gold stock, the breccia pipe and the impregnations. The mineralization areas are bordered by extended hydrothermal transformation aureoles : argillisa- tions, silicifiations, adularisations, carbonatations, sericitisations, pyriti- satios and alunitisations. Recently, direct and indirect Information has been accumulated, pointing to the relationship between the mineralizations and the volcanic structures, to a less extent, and the intrusive processes to a greater extent, revealed only by subvolcanic types so far. The complexity and great variety of the geological features of the Baia Mare area, due to numerous tectono-magmatic processes, re- quired its study by using geophysical data, mainly gravimetric and magnetometric, correlated with direct geological and petrophysical ones. The method adopted for the detailed study of some metallogenetic structures was based on the elaboration of mathematical models of si- mulation of the geological sources, responsible for the registered gravi- metric and magnetometric anomalies. Although they refer to local instances, these models have been selected as illustrative of the whole investigated area. The models have been chosen by taking into account the following main criteria : appropriate geological study by means of outcrop data correlated with drilling and mining ones, appropriate study of petrophysical features of rocks and formations — density and mag- netic susceptibility —, significant contrasts among the various com- ponents of the geological structure and their bi- or tridimensional nature. Among the sectors which agree with the above mentioned cri- teria, the following are to be discussed in the present paper : Tarna Mare-Turt, Herja-Baia Sprie, Cavnic-Roata and Băiuț. Simplified geolo- gical sketches, each accompanied by three sections pointing to the level Institutul Geological României ICR c 3 c o c ș c S ■g ’Sb O o (D O I 10 o C S Q O Q 0£ O CD £ c .2 S ? o c E 6 a >> c s as a o E Q> £ 5 £ 35 g X x; o x 2 pyroxene andesites; 9, overthrust; 10, contour of study areas. ce' C

= 0.1—0.3 to 0.8—0.9 ; S = 0.4—0.7). Diagenetic transformations alter. especially, the groundmass constituents. Arenites, from coarse- to fine-grained, include all petrographic types : greywackes, arkoses, lithic sandstones and quartz sandstones. Greywackes abound in the middle series of lithologic columns of Assyntic flysch deposits ; their composition varies from lithic (chlorite, biotite) to 1 University of Bucharest, Faculty of Geology and Geography, Bd. Bâlcescu 1, Bucharest. 2 Institute of Geology and Geophysics, str. Caransebeș 1. 78344 Bucharest. ic al României \J6R 44T> N. ANASTASÎU. D. JtPA 2 feldspathic (plagioclase Ans-20%) (± sphene, staurolite, zircon, clinozoi- site) and the binding material is represented by a chlorite-rich silici- ciastic matrix ; Q : F : L ratio varies continuously (Fig. 1). They are cha- racterized by a low sorting degree (o = 0.7—2). Diagenetic transfor- mations are also varied (anchimetamorphic recrystallization, silicification, epitaxy, authigeneses — pyrite, chlorite, chalcedony). As concerns the Institutul Geological României 3 SOURCE-AREAS-ASSYNTIC FLYSCH 447 arenitic series, the variation of quality in sandstones is reduceri ; the individualizătion of above mentioned petrotypes is the result of quanti- ’talibe variation of Q, F, L (Fig. 1) ; the same constituents are to be found in siltites or even lutites. Quartz occurs as granoclasts with straight and undulatory ex- tinction and oriented inclusions. Usually feldspars are represented by low alteration degree and in places by orthoclase or fresh microcline. The lithic fragments are of the same nature as those of rudites. The roundness of granoclasts is often of reduced value (R(1 = 0.5— 0.4) and the sphericity is not a significant parameter (S = 0.2—0.8). The sorting is variable (c = 0.5—0.75 in the case of quartz sandstones and 0.7—1.5 in the case of arkoses and lithic sandstones). The binding material of arenites is represented by siliceous (chal- cedcny) or chloritic (recrystallization chlorite) cement. Mineralogical Data Natura of granoclasts (quartz, feldspars, chlorites) Quartz is abundant (60—90%) in all epiclastic types and occurs, almost usually. as granoclasts with undulatory extinction which points to a source-area containing rocks that underwent mechanie deformation or cthers with straight extinction of magmatic origin (with zircon in- clusions). Feldspars, frequently occurring in conglomerates, greywackes and arkoses constituie several associations : — plagioclase (Ans-i.Q-microcline, in terrigenous series at Istria, Tașaul, Crucea. Saraiu, Războieni (Fig. 2) ; — plagioclase (Ân5-m)-orthoclase (2V = 63—68°) in arenites at Beidaud, Ciamurlia. Runcu. and exclusively as — plagioclase (An5-15) in sandstones and conglomerates at Sibi- oara, V. Alecsandri, Războieni, Rahmanu. Secondary transformations (kaolinization, sericitization) affected partly the plagioclases, the ortho- clase in places and never the microcline. Plagioclase is twinned according to Albite and Albite-Carlsbad laws and does not exhibit zoning. Its optical properties assign it to low temperature elements, characteristic of plutonics and “low grade ” meta- morphic rocks. Orthoclase, partly Carlsbad twinned, shows optical features cha- racteristic of subsequent granitoids. Microcline is always easy to identify due to its quadrille structure and is characteristic of gneisses and crystalline schists associated gneis- ses. No feldspar granoclast allows the identification of features characte- ristic of pyroclastic rocks. Chlorite, as granoclasts with obvious deformation traces (curved cleavages, anomalous extinction) occurs in all the rocks accompanied by biotite or muscovite ; its features of standard mineral of low grade metamorphic facies are obvious ; it also occurs as secondary product on biotite. Fig. 2 — Main transport directions of feldspars (plagioclase represented by rec- tangles with horizontal lines, microcline represented by grating) and lithoclasts (M — igneous ; Me — metamorphic ; S — sedimentary) in Central Dobrogea Massif (“greenschist” zone). Institutul Geological României 5 SOURCE-AREAS-ASSYNTTC FLYSCH 449 Nature of lithoclasts The lithoclasts of coarse-grained arenites and rudites may be de- termined and belong to rocks of different origins (plutonic, volcanic, metamorphic and sedimentary). The lithoclasts which represent plutonite fragments are the most frequent and exhibit the following mineralogical associations and struc- tural features : — plagioclase (An5.10) + quartz, in plagigranites with allotrio- morphic granular structure and massive texture ; — orthoclase + albite + quartz, in pegmatites with graphic structure ; — microcline, perthite microcline + plagioclase (Ant0-l5) + quartz, in calc-alkaline granites with medium allotriomorphic and microgranular structure (in aplite facies) ; — plagioclase (An 15) + orthoclase + quartz + biotite, in grano- diorites with hypidiomorphic medium granular structure ; — plagioclase + quartz in myrmekite intergrowths. The volcanics fragments are scarce and belong to tachylytic rocks, of albitophyre type (plagioclase — An5-8 + orthoclase in radial inter- growths) with partly porphyry structure and flow-bostonitic texture in the Tașaul and Izlaz conglomerates, dacites (plagioclase phenocrysts and corroded quartz in a microcrystalline groundmass) with porphyry struc- ture in the Sibioara Conglomerates. The lithoclasts which represent metamorphite fragments are less frequent and include mineralogical associations typical of : — gneisses (microcline + oligoclase + quartz + biotite ± stauro- lite) in the Sibioara Rudites ; — micaschists (biotite + muscovite + quartz ± oligoclase) ; — quartzites in rudites and lithic sandstones at Sibioara and Ciamurlia ; — phyllites (chlorite + sericite + quartz) in rudites at Izlaz and Palazu Mic ; — retromorphics (biotite + chlorite + oligoclase + albite + quartz) in the Palazu Mic Epiclasts. The lithoclasts resulting from sedimentary rocks are quite relevant and belong to highly diagenized quartzose sandstones (the granoclasts of which exhibit suture joints) at Tașaul, Sibioara and Palazu Mic, to sub- arkoses, at Tașaul and Izlaz and to siltic rocks, rich in quartz and mica, with obvious profound anadiagenetic transformations (it is difficult to assign them to silicolites or to metasiltites ; these polymetamorphic par- ticles may stand for siliceous remobilizations of diagenetic nature abounding in chalcedony ; they often exhibit concave-convex joints with surrounding granoclasts and lithoclasts). Some rudites contain shale pebbles which represent resedimented lutites of intrabasinal origin. The binding material of epiclastic rocks is of matrix and cement nature. The matrix (ortho- or epimatrix) includes chlorite, sericite, iron hydroxides and a few carbonates. The cement is siliceous (opal and/or chalcedony) and impure due to iron hydroxides. Structuralîy it is a 29 — C. 667 21 Ă Institutul Geologic al României XJGR/ 450 N. ANASTASIU, D. JIPA 6 Fig. 3 — Spatia! distribution of arenite types in Centrai Dobrogea Massif. At the base of each Q-F-L triangle, the binding material (black)-grains (white) ratio is shown ; on the left side of the triangle — main constituent minerals of the binding material (Se — sericite ; CI — chlorite ; Si — opal or chalcedony ; Fe — iron hydro- xides ; Cc — calcite). Other signs : 0, Md or mean diameter of graans ; So, grain size sorting as standard deviation ; Ro, grain roundness index. Institutul Geological României 7 SOURCE-AREAS-ASSYNTIC FLYSCH 451 basal binding material, partly film-like (when micas occur round grano- clasts and lithoclasts ; the increased frequency of these particles leads to the decrease of interstitial areas and thus to the constitution of pore cement). Within a complete epiclastic sequence one notes this tendency starting from base to its top. The transition from basal to pore binding material is graded within complete sequences starting with rudites, con- tinuing with greywackes and arkoses and ending with quartzose sand- stones ; the areal distribution of rocks (Fig. 3) exhibits no principie of frequency of binding material or sedimentary particles, Sedimentary Structures The terrigenous sequences in the “greenschist” area exhibit fre- quently a rhythmic character and an arhythmic one at Sibioara. The rhythms are incomplete, normal and accidental and exhibit centimetric and metric thicknesses ; complete rhythms and macrorhythms are rare (Jipa, 1970). Within rhythmic sequences the depositional structures consist of simple, normal graded-beddings — either continuous or discontinuous —■ cross laminations and rarely convolute laminations (at Năvodari) and frequent current ripples ; imbrications and sliding structures were iden- tified at Sibioara. Erosional structures are represented by direcțional markings due to paleocurrent erosion (flute marks) or to the objects transported (drag marks, chevron marks). Direction measuring of cross laminations, current ripples and sole markings (especially flute marks and drag marks) account for three pa- leocurrent systems : east to west, south to north, west to east and for the role of current transport (suspension and traction) and mass trans- port in the dynamics of sedimentary material (Jipa, 1970). Reconstruction of Source-Areas The petrographic study of epiclastic formations correlated with the sedimentary structures allows a discussion on possible source-areas and on their position as compared to the Assyntic “greenschist” basin. By reconstructing current directions one distinguishes three pos- sible sources of terrigenous material (Fig. 4) : — a western source, the farthest one, which supplied the material to the northwestern area of the basin ; — a southem source, probably the nearest one, which generated the coarse-grained material and — a northern source which supplied the fine-grained material. Their petrographic nature was heterogeneous from the very be- ginning and their erosion was rapid. Extrabasinal sources are characte- rized by highly metamorphosed crystalline schists (staurolite gneisses, gârneț micaschists), low metamorphosed ones (phyllites, quartzites) and associated plutonics of quartz-feldspar composition (granitoids, pegma- tites). The nature and optical features of feldspars (absence of plagio- 452 N. ANASTASIU, D. .TIPA 8 clases that exceed 20% An) account for a source-area in which basic rocks were absent and volcanics oocurred in places. The occurrence of the latter in the source-area is obvious (trachyte and dacite lithoclasts) and points to probably pre-Assyntic volcanic activity ; the structural facies of flow and porphyry volcanics accounts for the effusive nature of rocks from the source-area. The alkaline trend of lithoclasts-sie- Fig. 4 — Location of source areas in respect of the As- syntic basin. 1. Scythian Platform; 2, Moe- □lan Platform. nites/trâchytes points to consanguinity relations between plutonic and volcanic products. The sedimentary rock lithoclasts (quartzose sandstones, arkoses, siltites) in “greenschist” rudites and arenites prove the conservation in extrabasinal source-areas of a sedimentary cover emerged during the Assyntic and accumulated prior to it ; this is one of the few proofs of the nature and occurrence of some Precambrian unmetamorphosed sedi- mentary rocks, in adjacent areas. These lithoclasts seem to be the oldest sedimentary rocks reported from a geological formation in our country. This petrographic configuration corresponds partly to the Nipru- Bug Series (granitoids) and the Krivoirog Series (phyllites and retro- morphics) and/or to the Ovruci Series (sandstones) in the Scythian Platform (Ucrainian craton) and to their Middle or Lower Proterozoic equivalent from the basement of the Moesian Platform. The variation of grain size (Md, o-) and morphometric parameters (Ro, S) of terrigenous deposits in Central Dobrogea Massif may be used, together with the other structural features, as marker of the location of the source-area related to the basin and of the dynamics of sediments to or within the basin. Thus, proximal, coarse facies prevail in the neigh- bourhood of source-areas, in the south and south-east of Central Do- brogea Massif, while distal, fine-grained ones occur in the north and northwest ; from petrographic point of view, the terrigenous deposits Institutul Geologic al României 9 source-areas-assyntic fl.ysch 453 exhibit a lithic and a feldspathic facies. According to the degree of roundness, some quartz, feldspar, heavy mineral granoclasts point to the reworking of former sedimentary material, while the lithoclasts with no petrographic equivalent in supposed sources, show small values of the roundness degree which point to the transport from an intra- basinal area. The correlation of data — great thickness of Assyntic flysch de- posits (5000 m), swift transition from proximal to distal facies, occur- rence of shale pebbles, volcanic lithoclasts and matrix as main binding material of terrigenous rocks — shows that sediments accumualted in a basin larger than present-day Central Dobrogea and of variable depth. The coexistence of various current systems in the same area accounts for the presence of a fla,t accumulation area in central zones. The evo- lution of Central Dobrogea Massif — inserted between two important crustal sectors : Scythian Platform and Moesian Platform — may be regarded as starting from a probably intracontinental basin with in- active margins, below which incipient suborustal erosion processes led to the thinning out of lithosphere and the initiation of active subsidence (which favours the accumulation of thiek sediment piles). The morphological configuration of this basin should also include intrabasinal elevations which acted intermittently as sources of material and influenced the dynamics of currents and mass transported material. The alkaline volcanic lithoclasts should be considered as reworked pro- ducts from neighbouring areas, already stable, and not as an expression of intrabasinal manifestations. A Institutul Geologic al României JGR/ Institutul Geological României Sedimentologie LARGE SCALE PROGRADATION STRUCTURES IN THE ROMANIAN CARPATHIANS : FACTS AND HYPOTHESIS BY DAN JIPA 1 Investigation of the sedimentary structures advanced rapidly. Dur- ing evolution al] efforts have been directed to the description and inter- pretation of the small scale features. The very large sedimentary struc- tures belong to the field of megasedimentology. As “microsedimentology” still have much knowledge to accumulate, megasedimentology is totally neglected. The present author had the opportunity to identify several sedi- ment accumulations produced by large scale progradation. In this way he felt stimulated to approach the difficult field of megasedimentology. Progradation Structures Recorded in Romania Bucegi Conglomerates (Albian) Located at the bend of the Romanian Carpathians (Fig. 1 A), the Bucegi Mountain is geologically made up mostly of an Albian conglo- meratic sequence (Patrulius, 1969). Known as the Bucegi Conglomerates this sequence consists of a monoclinal alternation of conglomeratic, sandy and silty lithologic horizons. The Bucegi conglomeratic Complex is supported by an Aptian de- trital formation mainly consisting of an alternance of thin bedded sand- stones and marls. At the upper part of the Aptian formation Patrulius (1969) separated a distinctive intercalation of calcareous rudites, named the Raciu Breccia. This intercalation discontinuously occurs at the same stratigraphie level all over the Bucegi Mts area. Due to detailed litho- logic mapping (Patrulius, 1969 ; Jipa, 1982), it has been pointed out that the various major lithologic horizons representing different levels of the Albian sequence are coming in direot contact with the underlying Aptian deposits (Fig. 1 B). Moreover, most of these lithologic horizons rest on the 1 Institute of Geology and Geophysics, str. Caranesbeș 1, 78344 Bucharest. 456 D. JIPA Fig. 1 — Broad primary structural features of the Bucegi Conglomerates. A, index map ; B, geological sketch of the Bucegi area (largely simplified, after Patrulius, 1969 ; Jipa, 1982). Albian deposits : 1, siltites ; 2, sandstones ; 3, upper level conglomerates ; 4, lower level conglomerates ; 5, Aptian deposits (triangles = Raciu Breccia) ; 6, crystalline rocks ; 7, direction of geological section : C, longitudinal geological section : D, same section in the concept before progradation was documented. Institutul Geological României 3 LARGE SCALE PROGRADATION STRUCTURES 457 same Upper Aptian level, materialized by the Raciu Breccia. Relying on these data, Jipa (1982) conclud'ed that the Bucegi Conglomerates repre- sent a very large, oblique bedded formation (about 40 km long and more than 1 km thick). Every lithologic Albian horizon consists of prograding deposits lying down on the inclined surface of the previously accumu- lated sediments, reaching beyond these sediments the basal accumulation surface (represented by the Aptian/Albian limit) (Fig. 1 C). The documentation of the progradation structure of the Bucegi conglomeratic sequence resulted in the modification of the previous ideas concerning the thickness of the sequence. Before realizing the progra- dation action, the Albian deposits appeared as a simple monoclinal se- quence (Fig. 1 D) ; consequently, its stratigraphic thickness amounted more than 8000 m. The real thickness of the prograded Albian formation is to be measured perpendicularly on the basal surface (that is the Aptian/Albian limit). In this way the thickness of the Bucegi conglome- ratic complex is only 1200—1500 m. Lower Red Clay Complex The Paleogene deposits from the north-western Transylvania make up two rhythmical megasequences. Each sequence originates with red continental deposits, continues with evaporitic facies and ends with ma- rine deposits (Răileanu, Saulea, 1956). The lower Red Clay Complex (Pa- leocene-Ypresian) consists of red lutites, arenites and rudites. The lower red deposits nearby the Agîrbiciu village (about 25 km west of Cluj ; Fig. 2 A) are dominantly coarse grained, made of rudaceous beds (up to 5 m thick) with red silt intercalations. The coarse grained red deposits at Agîrbiciu are overlain by a dolomitic oolite intercalation (Popescu, 1976) known as the Agîrbiciu Limes tone. The detailed survey of the Red Clay Complex at Agîrbiciu revealed that the rudite beds are oblique as compared with the almost horizontal Agîrbiciu Limestone (Fig. 2 B). Consequently, within the investigated area the lower Red Clay Complex represents a body (of about 2 km visible length) with large scale oblique stratification. The existence of this oblique megastructure indicates that at least a part of the Paleocene-Ypresian continental deposits have been accumu- lated as alluvial fans, at the base of the marginal slope of the Transyl- vanian Basin (Fig. 2 D). The detection of the progradation effects is also important from the structural viewpoint. It was assumed so far that the Paleogene strati- graphic units extended throughout the whole (or most of) the Transyl- vanian Basin (Fig. 2 E). The progradation structure suggests that the red Paleogene facies is restricted to the marginal area of the basin (Fig. 2 E). _jT A Institutul Geological României \ igr/ 458 D. «TIPA 4 Fig. 2 — Primary structural features of the lower Red Clay Complex of north-western Transylvania. A, index map ; B, ruda- ceous beds of the lower Red Clay Complex in the Agîrbiciu area (a, Agîrbiciu Limestone ; b, red rudites ; c, red siltites) ; C, de- tailed cross-section at Agîrbiciu : D. interpreted accumulation environment of the red clay deposits ; E, simplified, classic geo- logical cross-section through the Paleogene deposits of north- western Transylvania ; F, same section in the progradation con- cept of the lower Red Clay Complex (Pgi-y). Institutul Geologic al României LARGE SCALE PROGRADATION STRUCTURES 459 Getic Paleogene Deposits The Getic Depression is the term applied to the area with mostly Tertiary deposits located to the souith of the eastern part of the South Carpathians (Fig. 3 A). The basal, conglomeratic facies of the Getic Eo- cene shows important thickness variations. Two large rudaceous bodies occur at the eastern and western extremities of the Getic Paleogene area. The thick body (700—800 m) in the eastern end is rapidly thinning out toward the west, to about 50 m of rudites. Farther westwards, another smaller (300—400 m thick), lens-like body of rudites is shaping out (Fig. 3 B). Between the two extreme, important rudite accumulations there is a zone where arenaceous sediments completely replace the ru- dites. In some well exposed and large enough outcrops, cross stratifi- cation at the scale of the w’hole rudite body was observed. Transport directions of the rudaceous material are dominantly towards south-east (Fig. 3 C). All these data indicate that the rudaceous Eocene material accumulated at the shelf margin as marine shallow water fans. Within the concept of Paleogene deposition as sedimentary cones the basal conglomerate facies represents the inner fan zone, the overlying sandstone facies appears in the middle fan zone, the marly facies oc- curring in the outer fan and the fan plain zone (Fig. 3 D). The occurrence of coarser gained deposits — for example the Oligo- cene Corbi Sandstone — within the marly Paleogene facies, with local distribution (Murgeanu, 1941), is also explained by the fan sedimentation concept. Such coarse grained deposits represent the elastic material accu- mulated on the distal slope of the fan (Fig. 3 E). The Corbi arenaceous body was laid down through only one channel distribution net, be- longing to a single, active fan. This explains the local occurrence of the Corbi Sandstone and its wedge-like shape. Hypothesis on Very Large Scale Progradation in the Romanian Carpathians During their postgeosynelinal rising, in front of the Carpathians there accumulated large quantities of elastic sediments. According to the thickness determined by the usual stratigraphie standards, huge sedimen- tary piles — many kilometers thick — have been accumulated in very shallow sedimentary basins (several metres or tens of metres deep). Con- sequently, a conflict between the quantity of sediments versus the hous- ing capacity of the sedimentary basins is clearly shaping out. To explain this conflict the subsidence phenomenon is invoked. An alternative, Institutul Geologic al României 460 D. JIPA 6 Fig. 3 — Primary structural features of Paleogene deposits (Getic Depression). A, index map ; B, thickness variation of the Eocene conglomerates and the presumed locations of the main rudaceous fans ; C, paleocurrent directions ; D, genetic interpretation of Getic Paleogene facies ; E, genetic interpretation of genesis and distribution of the Corbi Sandstone (Oligocene). Institutul Geological României 7 LARGE SCALE PROGRADATION STRUCTURES 461 rațional explanation is now accessi'ble, taking into account the possibility of progradation action developed at the scale of the mountain chain. When progradation is demonstrated it leads to an entirely new concept on the geological structure of the investigated area. The following two hypothetical large scale applications of progra- dation to explain the accumulation of some Carpathian sedimentary se- quence are based on two different progradation mechanisms. Sediments of the Getic Depression According to the above presented arguments, the accumulation of the Paleogene deposits in the Getic Depression took place by progra- dation. The Getic Upper Cretaceous to Pliocene deposits make up — to- gether with the Paleogene deposits — a homoclinal series dipping away from the crystalline core of the South Carpathians (Fig. 4 A). This fea- ture suggests that progradation might have been active for all Getic, Cretaceous to Pliocene deposits. In such circumstances, the sediment accumulation front advanced laterally, away from the source area. Con- sequently, a constructional shelf area appeared (Fig. 4 A), producing the southward migration of the axis of the sediment acumulation zone. The current directions recorded in the Getic Cretaceous to Pliocene deposits are in agreement with the progradation direction. Milcov Formation Sarmatian-Pleistocene deposits occurring in front of the East Car- pathians (Fig. 4 B). between the Trotuș and Buzău valleys, have been named the Milcov Formation (or Beds). This formation, constantly dip- ping eastwards, is involving the same conflict between its stratigraphic thickness (about 10 000 m) and depositional depth (several metres). It appears, then, that the accumulation of this formation could be analysed in connection with the progradation proeess. The paleocurrent directions of the Milcov Formation are mostly (longitudinal towards the south. This feature does not agree with the supposed eastern progradation of the formation. But the Sarmatian- Pleistocene sedimentation is synchronous with the very active uplift of the Carpathians. A horizontal, eastern component of the rising movement was for a long time considered (Lăzărescu, Dinu, 1983). The rising and lateral shifting of the Carpathian source area resulted in an eastward migration of the sedimentary basin, possibly leading to a progradation structure (Fig. 4 B). This is a special type of progradation, governed by the direct intervention of tectonic forces. C . JA Institutul Geologic al României ÎGR 462 D. JIPA 8 Fig. 4 Institutul Geological României 9 LARGE SCALE PROGRADATION STRUCTURES 463 REFERENCES Andreescu I., Țicleanu N. (1969) Harta geologică a R.S.R., scara 1 :50 000, foaia Dumitrești. Archives of the Institute of Geology and Geophysics, București. Jipa D. (1982) Conglomeratele de Bucegi — exemple de formațiune oblic stratifi- cată. D. S. Inst. geol. geofiz., LXVI, București. Lăzărescu V., Dinu C. (1983) Characteristic Stages and Formations of the Roma- nian East Carpathians Evolution. An. Inst. geol. geofiz., LX, București. Macarovici, N., Motaș C. I., Contescu L. (1967) Caracteres stratigraphiques et sedi- mentologiques des depots sarmato-pliocenes de la courbure des Carpathes Orientales. An. șt. Univ. „Al. I. Cuza“, Secț. II, XIII. Murgeanu M. G. (1941) Recherches geologiques dans Valea Doamnei et Valea Vâl- sanului (Mountenie Occidentale). C. R. Inst. Geol., XXVI, București. Patrulius D. (1969) Geologia masivului Bucegi și a culoarului Dîmbovicioara. Edit. Academiei R.S.R., București. Popescu B. (1976) Lower Gypsum Formation West of Cluj — a Supratidal Evapo- rite. Sedimentological and Petrographic Approach. An. Inst. geol. geofiz., XLVIII, p. 97—114, București. Răileanu G., Saulea E. (1956) Paleogenul din regiunea Cluj și Jibou (NV bazinului Transilvaniei). An. Com. Geol., XXIX, București. Fig. 4 — Hypothetic progradation structure of some Carpathian sedimentary units. A Getic Depression : a, geological sketch of the Getic Depression (K, crystalline basement ; Cr, Cretaceous ; Pg-Aq, Paleogene-Aquitanian ; M, Miocene ; P, Plio- cene) : b, idealized cross-section of the Getic Depression assuming progradation action’ (not to scale) ; B, Milcov Formation : a, geological sketch, after Macarovici et al 1967 (M, Miocene; hatced = Milcov Formation — Sarmatian to Lower Levantine ; Lv, Upper Levantine ; paleocurrent diagram of the Milcov Formation.) ; b presumed mechanism of progradation determined by the rising and shifting of the East Carpathians (not to scale) ; c, interpretation of a symbolic cross-section of the Milcov Formation (1) in the classic way (2) and in the progradation con- cept (3). Institutul Geological României Institutul Geological României Sedimentologie A FLUVIAL SEDIMENTATION MODEL — THE DANUBE DELTA BY NICOLAE MIHĂILESCU \ CONSTANTIN ROGOJINĂ 1 The Danube Delta is bordered northwards by the Bugeac Platform, south-westwards by the North Dobrogea hills and south-eastwards and eastwards by the Black Sea. It has a surfaee of about 5460 km2, of which 60—70% is covered by water. The multiannual flow discharge value, at the delta top (Ceatal Iz- mail), is of 6 300 m3/sec., while the maximum levels in May reach 10 000 m3/sec. and the minimum levels in October lower to 3 250 m3/sec. (Diaconu et al., 1963 ; Bondar, 1972). The flow discharge is distributed as follows : 62.5% along the Chilia branch and 37.5% along the Tulcea branch ; at Ceatal Sf. Gheorghe, it amounts to 22% for the Sf. Gheorghe branch and to 15.5% for the Sulina branch. The Danube Delta is geographically and geologically a terminal plain, a result of the variation of the Black Sea level during the Post- glacial age. The river, the sea, the wind and the vegetation exercised a combined action related to the variation of the Black Sea level, and the detrital deposits were set on a loess plain (Mihăilescu, Banu, 1957). The Lower Quaternary deposits (Liteanu et al., 1961) of the delta basement are overplaced on a relief (Fig. 1 a) formed of an old hydro- graphic network (the Danube, Katlabug, lalpug and Kitaj valleys). They are formed of gravels and boulders (Fig. 1 b), 0.70—37.70 m thick (Li- teanu, Pricăjan, 1963). The drillings have shown (Liteanu et al., 1961, 1963) the presence of loessoid deposits northwards (Stipoc) and southwards (Razelm Lake) the delta, over the gravels. In the central zone of the delta the loessoid deposits were subsequently eroded (Fig. 1 c). The loess of the northern zone of the delta (Chilia Veche) is a continuation of that from the Bu- geac Platform and southwards the delta (Mihăilescu et al., 1984) the con- tinuation of loessoid deposits from North Dobrogea. These deposits, of a continental origin, are those where Antipa (1912) noticed some frag- ments of Elephas primigenius B 1 u m b. and Rhinoceros antiquitatis B 1 u m b. (Sulina canal — Mile 12) in their basement. 1 Institute of Geology and Geophysics, str. Caransebeș 1, 78344 Bucharest. 30 — c. 667 Institutul Geological României \ 1GR 466 N. MJHAELESCU, C. ROGOJINA Fig. 1 — Structural maps of the Danube Delta (after Liteanu, Pricăjan, Baltac, 1961 ; Liteanu, Pricăjan, 1963 ; archives of the Ministry of Geology and IGCL, Tulcea). a, pre-Quaternary basement ; b, Lower Pleistocene deposit top ; c, loessoid deposit top ; 1, limit of the Danube Delta territory ; 2, isobaths ; 3, deposit altitude. Institutul Geological României 3 A FLUVIAL SEDIMENTATION MODEL-DANUBE DELTA 467 The core samples prelevated from the lakes northwards the Sulina canal have shown the presence of loessoid deposits (Fig. 1 c) under the present-day delta structure (Antipa, 1912 ; Mihăilescu, 1984). These de- posits contain rare terrestrial gastropods ; they are completely lacking in foraminifera and contain rare fresh water algae and spore granules simi- lar to those from the loessoid deposits of the Moldavian Platform The deltaic deposits are represented by levels and lenses of sands and silts, in a succession with numerous lateral varieties of facies (Li- teanu et al., 1961 ; Liteanu, Pricăjan, 1963), They were previously con- sidered of the Upper Pleistocene (Mutihac, Bandrabur, 1967) or Holo- cene (Panin, 1974) age. At the beginning of the Holocene age the “inițial spit” was formed (Vâlsan, 1934). This spit separates two sedimentary domains : a fluvial- lacustrine domain westwards and a marine domain eastwards. Our available data (drillings, core samples) show that both marine and flu- vial-lacustrine sediments overlie : — coarse-grained deposits formed of gravels and boulders (mainly on the borders of North Dobrogea hills) ; — loessoid deposits (northwards the delta and on the borders of the Razelm-Sinoe lakes). Therefore, we think that the “inițial spit” was not accidentally formed here, as it is based on loessoid deposits (Antipa, 1912 ; Murgoci, 1912 ; Mihăilescu, 1984). In places where the base was not “sufficient”, this spit was pierced by the Sf. Gheorghe branch. At the end of the Neoeuxin stage (Upper Pleistocene-Lower Holo- cene) the “cuspate” Sf. Gheorghe I Delta was formed (Panin, 1974). The Caraorman Formation represents the northern part of this delta (Panin, 1974) ; this formation overlies loessoid deposits (Mihăilescu et al., 1974). The Southern part of this delta, in the Sf. Gheorghe branch-Razelm zone, is also superposed on loessoid deposits (Mihăilescu et al., 1984). The Phanagorian regression, during which the Black Sea level went down to 3—4 m, had as a result the formation of the Sulina Delta struc- ture (Panin, 1974). At the beginning of the Histrian transgression (Bleahu, 1963), the «flow and solid discharges of the Sf. Gheorghe branch grew and the Sf. Gheorghe II Delta (Panin, 1974) was formed. At the same time the Chilia branch started the formation of its own delta. The present-day morpho-hydrographic features will be discussed in relation to the planar geometry of the meandering channels. Measure- ments of morphometric parameters were made on maps 1 : 25 000 and 1 :50 000. 1. The behaviour of the meander curvature of the Sf. Gheorghe branch is compared to the harmony imposed by a “sinus-generated” curve (Leopold, Langbein, 1966). It is illustrated by the projection of the angular deviation of the small successive segments of the channel from the average direction of the meandering “valley”3, in relation to the distance measured along the river bed (Fig. 2). The study of this dia- gram has pointed out the existence of four segments having characte- ristic configurations : a) between km 15—22 a limited meandering segment Pi Institutul Geologic al României k 16 r7 N. MIHAILESCU, C. ROGOJINA 4 A FLUVIAL SEDIMENTATION MODEL-DANUBE DELTA 469 (Panin, 1976) ; b) between km 22—49, a free meandering segment, in accordanee with the present-day direction of the meandering “valley” ; c) between km 49—85, a free meandering segment, not following the present-day direction of the meandering “valley” ; d) between km 85—92, a limited meandering segment. TABLE 1 Aoerage morphomctrical parameters and relationships among these parameters for different rea- ches of the Dannbe Delta Reach N rc (m) w (m) rc/w N (m) A (m) Â/w A/w X/rc Chilia (km 30-70) 12 1G79 363 5 .1 7 4282 803 11 .6 2.2 2.7 Chilia (km 74-116) 12 1250 100 3.0 G 5204 1858 13.0 5.0 4 .2 Paleo-Suluia 8 731 142 5.3 8 4897 1554 40.3 21.0 4 .9 Tuleca 5 1260 420 2.8 3 3775 766 8.9 1 .8 3.3 Sf. Gheorghe (km 25—44 .5) 13 985 242 3.9 4 3005 2926 13.6 13.8 4.3 Sf. Gheorghe (km 14.8 — 84) 16 875 289 2 .8 5 3315 2320 11.7 8 .6 4.9 Sf. Gheorghe (km 23-84) 29 930 2GG 3.3 9 3160 2630 12.5 11 .0 4.6 Symbols: N= number of measurements; rc= radius of curvature; w= width of channel; X— wavclength; A = wave amplitude. The Sf. Gheorghe segment between km 15—92 is generally a free meandering channel, slightly limited at extremities. The following mor- phometric analysis (Tab. 1) will deal with this segment only 4. Important significances have been attributed to the rc /w rela- tionship 5. The values of this relationship are between 0.6—8.8 with a theoretically determined average of 2.7 and a statistically determined average of 3.3. These data are very similar to those presented by Leopold and Wolman (1960) for rivers meandered in non-deltaic environments. The constancy of the X/r relationship along the whole course of a meandering river determines the regular aspect of meandering, this relationship being quoted with an average value of 4.7 (Leopold, Wol- man, 1960 ; Leopold, Langbein, 1966). For the meandering reaches of the Sf. Gheorghe branch, values from 3.1 to 7.3 were obtained with an average of 4.6 (Tab. 1). The X/w ratio has rather constant values for a large meander spec- trum, being mentioned with average values of 6.6 (Inglis, 1949, in Leo- pold, Wolman, 1960 and 10.9 (Leopold, Wolman, 1960). For the Sf. Gheor- ghe branch meanders an average value of 12.5 (9.2—16.4) was obtained, with a lower significance as compared to the other relationships men- tioned above. The above analysis shows that the Sf. Gheorghe branch, with a freely meandered bed in a “valley” unrestricted by major geomorpho- logical features can be characterized by a series of morphometrical para- meters with well established relationships between them. Institutul Geologic al României 470 N. MIHA1LESCU, C. ROGOJINA 6 2. The Chilia branch has apparently the configuration of a large meandered channel. The sedimentological and morphological analyses show that only a few upstream reaches freely meandered. Relationships among morphometrical parameters for this meandered reach of the Chi- lia branch (km 74—116) are defined by the average values rc /w = 3.0, Â/w = 13.0 and Â/rc = 4.2. These values are very similar .to those ob- tained for the Sf. Gheorghe branch (Tab. 1). The Chilia branch reach between km 30—70 is characterized by the ratio Ă/w = 11.6 (4.2—18.4). This value resembles the values of the meandered reaches of the Chilia branch (km 116—74) and the Sf. G,heor- ghe branch. The other parameter ratios have different values as com- pared to the meandered reaches values (Tab. 1). While comparing the data, one can notice that the re /w and ?,/rc ratios can characterize the freely meandered channels and can differentiate the freely meandering channels from the sinuous, apparently meandered channels. Paleogeographically speaking, these data raise the question if this freely meandered segment of the Chilia branch (km 116—74) is not the ancient bed of a former river. 3. The Tulcea branch crosses a meander “valley” with a well de- veloped divagation zone on the right side of the valley (Panin, 1976). The meandering evolution on the right side of the valley is limited by the lithological and morphological features of the geological unit of North Dobrogea. The r0 /w ratio with an average of 2.8 is very similar to our va- lues for the Sf. Gheorghe branch (Tab. 1). But meandering limitation influences both meander amplitude and wavelength as we can see while comparing the values >-/w. A/w and Vrc d of the Tulcea branch and of the Sf. Gheorghe branch (Tab. 1). 4. Meanders of the paleo-Sulina branch are located in a well li- mited divagation zone (Panin, 1976). The process of meander abandon- ment took place artificially during this century, following the rectification works of the Sulina branch, between 1868—1902 (Petrescu, 1957). By comparing the existing maps, one can notice that a filling up took place there, from upstream to downstream of the abandoned river channels. Now there are wholly or partly filled up river channels. The partly filled up beds have greatly diminished discharges, water flow being connected to the natural and artificial secondary channel network. The morphometrical parameters mentioned below concern only partly abandoned meanders, which are still occupied by water. The rc /w, k/w and A/w ratios have much larger values than those of the same ratios of the Chilia (km 116—74), Sf. Gheorghe and even Tulcea branches (Tab. 1). These anomalous values are mainly imposed by the decrease of present-day channel width, by discharge decrease and by filling up. The X/rc “ 4.9 ratio is very neai' to the values of meandered reaches in the Danube Delta (Tab. 1, 2), and proves to be less affected by recent modifications of the hydraulic geometry. The morphometric characters of the abandoned meanders were pre- sented by Panin (1976). For the Erenciuc Lake, our measurements have jA Institutul Geological României icRy A FLUVIAL SEDIMENTATION MODEL-DANUBE DELTA 471 shown that the rc /w ratio varies between 2.1—5.3, with an average of 2.8. Despite recent modifications of hydraulic geometry, the rc /w value is well correlated with the values obtained for the Sf. Gheorghe branch (Tab. 1). 5. The field reaches and the interpretation of maps have pointed out the existence of some secondary channels which seem to represent meandering beds (Fig. 3 a). TABLE 2 Average inorphomelrical parameters and the \/rc ratio for the main secondary channels of the Danube Delta Channd N l r° ‘ 1 (m) N (m) A (m) X/rc interval average ** Pardina 37 713 17 839 184 1 .5-7 .6 3.2 Tătaru 12 765 7 2021 312 2.0-5 .2 3.1 ** Gotca 14 432 8 1019 186 1.8-5 .7 3.0 *** Păpădia-Mitchina 22 246 14 754 204 1 .9-5 .5 3.5 * Sontea 18 234 9 891 231 2.6 — 8.4 4 .4 * Lopatna 60 170 29 514 162 1 .8-5 .8 3.8 *** Litcov— Perivolovca 25 442 11 1380 315 2 .3-8 .1 3.4 * Dunavăț. 34 301 20 1423 882 2 .8-7 .8 5 .1 * Dranov 17 281 7 1121 444 2 .4-6 .2 4.2 *** Zencova 9 238 5 1135 402 3.4-8.0 6 .0 * typical meandering channels; ** sinuous channels; *•* partly meandering channels The other symbols arc the same as in Table 1. The correlation diagram Z/rc for these channels (Fig. 3 b) shows an increase of point scattering. according to the increase of wavelength (for X/2 200 m). Between the X and rc values of a large number of rivers, some approximately linear relationships were noticed (Leopold, Wolman, 1960). The best-fit lines of Ă/re values, together with field observations (Fig. 3 a) have led to the separation of three types of secondary channels : a — Typical meandering channels : Dunavăț, Dranov, Șontea, Lo- patna (Fig. 3 b). These river beds have a good apparent correlation of values Ă/rc = 3.8—5.1. Small zones of meander divagation are preserved within adjacent areas of river beds ; b — sinuous channels : Pardina, Tătaru, Gotca. The  rc values have a large dispersion (Tab. 2), and the average values of these ratios are between 3.0 and 3.2, similar to the value of Ă/re = 2.7 of the sinuous reach of the Chilia branch (km 30—70) (PI.). Developed levees and cre- vasse-splay deposits are present in the adjacent areas where divagation zones are absent. These channels belong to the distributary system of the Chilia branch, and are grouped within the depression between the Stipoc Formation and the Chilia branch ; Institutul Geological României \ 16 R 7 472 N. MIHAILESCU, c. rogojina 8 c — partly meandered channels : Păpădia-Mitchina, Litcov-Peri- volovca, Zencova (PI.). Dispersion of Ă/re values (Fig. 3 a) and the ave- rage values of this ratio (Tab. 2) have an intermediary character as com- pared to the first two groups. On certain reaches of these channels re- stricted divagation zones have been preserved. Fig. 3 — a, Vrc diagram for secondary channels of the Danube Delta ; b, best-fit lines of the X/rc values for secondary channels of the Danube Delta ; dashed lines delimit the field of point scattering. Institutul Geological României <) A FLUVIAL SEDIMENTATION MODEL-DANUBE DELTA 473 6. The depressionary zones closed by the “inițial spit” changed into flood basins. Subsequently they were divided by the levees of the for- ming hydrographic network. The lacustrine sedimentation of the Danube Delta is located within zones which “become” depressionary due to en- closures made by levees or by fossil littoral belts. The lacustrine sedimentation is controlled on the one hand by the solid discharge favoured by the main branches of the Danube and on the other hand by the'composition of the lake basement. The lacustrine sedi- ments of the delta are most of all the result of some processes of re- moving and redeposition of detritus from their basement and of some diagenesis processes, connected to the Chemical composition of the older marine, brackish or continental deposits. Conclusions At the beginning of the Pleistocene, both the Danube and the lal- pug, Katlabug and Kitaj were forming a hydrographic network which concentrated towards a central depressionary zone (Fig. 1 a). During the Pleistocene, the lowering of the base level of those rivers flowing into the NW of the Black Sea allowed the activation of this hydrographic network, having as a result the display of a gravei nappe (Fig. 1 b). A loessoid deposit cover was formed in parallel and covered the whole NW area of the Black Sea border. During the Holocene, several partly superposed deltaic structures were formed on the present-day area of the Danube Delta, due to the repeated variation of the Black Sea level (Degens, Ross, ed.. 1974). During the Holocene time, a WNW—ESE oriented hydrographic network was formed on the relief formed of loessoid deposits. This is located between the North Dobrogea hills and the Stipoc-Chilia Veche zone (Fig. 1 c). In the meantime, on the eastern border of the loessoid deposits the “inițial spit” started to form, having behind a fluvio-lacus- trine sedimentary environment. The hydrographic network of the fluvio-lacustrine delta was drai- ned by a river bed which, at the same time with the formation of the Sf. Gheorghe I Delta, was going to get the orientation of the present- day Sf. Gheorghe “valley” (Pl. I). In this period a rotation took place in the direction of the Sf. Gheorghe branch “valley”, accompanied by a parțial, gradual avulsion of the former river beds. The Dunavăț, Dranov and Zencova channels can stand foi' the possible stages of this mi- gration (Pl.). During the Phanagorian regression, when the sea level lowered, the Sulina Delta formed. The piercing of the “inițial spit” and the modifi- cation registered in water flow distribution at the delta top (as a result of rotation in direction of the Sf. Gheorghe branch “valley”), have fa- voured the transformation of a secondary channel (paleo-Sulina) into a main branch of the Danube. As compared to the formation time of the Chilia Delta, the Chilia branch proves to have functioned as a main distributive branch of the Danube, after the formation of the Sf. Gheorghe and Sulina branches. The river bed configuration, the morphometric data and the morpho- Institutul Geologic al României X IGRZ 474 N. MIHĂILESCU, C. ROGOJINA 10 structural characteristics of the adjacent zones suggest that this branch is made of reaches which were formed during stages and at different limes. The Danube gulf “became” a gulf only at the end of the Pleisto- cene by the inundation by the sea of an older hydrographic network. This gulf was dammed by a first marine formation behind which a vast fluvio-lacustrine zone was formed. This fluvio-lacustrine zone developed in parallel to the evolution of the marine zone of the delta front. The main delta channels have divided the primary lake, have compantimented it, while the fluvial deposits (levees, accretion zones, divagation zones) have formed some emerged regions and the secondary channels have strengthened this proeess. The configuration of the present-day depressionary zones of the Danube Delta (PI.) is outlined by several morphological elements of Up- per Pleistocene (loessoid deposits) and Holocene ages : — relief of loessoid deposits (Chilia Veche, Stipoc) ; — relief of divagation zones of the Sf. Gheorghe, Sulina and Chi- lia branches ; — relief of fossil littoral bars which belong to various formations in time and — relief of present-day littoral bars. 2 Samples determined by St. Roman (I.G.G.). 3 The divagation zone of the Sf. Gheorghe branch (Panin, 1976) is consi- dered in this case as a meander “valley”. Brice (1974) found out that the planar evolution of meanders is generally reauced to a descendent migration, an amplitude growth and a “cut-off”. These modifications are well characterized by the following morphometrical pai-ameters : radius of curvature (rc), bed width (w), wavelength (Z) and meander amplitude (A) (as defined by Leopold, Langbein, 1966, with specifications made by Hickin, 1974, and Brice, 1974). 5 The relative constancy of the rc /w ratio for all meandered rivers is con- Șidered to make them seem very similar on maps. On the other hand, Hickin (1974) and Hickin and Nanson (1975) have shown that the evolution and the mi- gration ratio of these meanders are controlled by certain values of the r /w ratio. 6 Relationships among morphometrical parameters have been defined by equations of P = kR" type, where P is Z or A, R is w or r and k is a con- stant. As the a exponent varies between 0.98—1.10 in all equations (Leopold. Wol- man, 1960), jt could be approximated as unitary and thus relationships become linear (Fig. 3 b). REFERENCES Antipa Gr. (1912) Cercetări hidrologice in România și importanta lor științifică și economică. Discursuri de recepție. Academia Română, 37, București. Bleahu M. (1963) Observații asupra evoluției zonei Histria în ultimele trei milenii. Probleme de geografie, IX, 45—56, București. Institutul Geological României 11 A FLUVIAL SEDIMENTATION MODEL-DANUBE DELTA 475 Bondar C. (1972) Contribuție la studiul hidraulic al ieșirii la mare prin gurile Du- nării. Studii de hidrologie, XXXII, 466 p., București. Brice J. C. (1974) Evolution of meander loops. Geol. Soc. Am. Bull.. 85, 4, 581—586, Boulder. Candido J. C. (1971) Contribuițao ao dos meandramentos fluviais. Noticia geomorfo- logica, 11, 22, 1—84, Campinas, Brasil. Diaconu C.. Nichiforov I. D. (Ed.) (1963) Zona de vărsare a Dunării. Monografie hidrologică. Ed. tehnică, București. Hickin E. J. (1974) The Development of Meanders in Natural River-channels. Am. Jour. Sci„ 274, 2, 414—442, New Haven. — Nanson G. C. (1975) The Character of Channel Migration on the Beatton River, Northeart British Columbia, Canada. Geol. Soc. Am. Bull., 86, 2, 487—494, Boulder, Leopold L. B., Langbein W. B. (1966) River Meanders. Sci. Am., 214, 6, 60—70, San Francisco. — Wolman M. G. (1960) River Meanders. Bull. Geol. Soc. Am., 71. 6. 769—794, Liteanu E., A. Pricăjan (1963) Alcătuirea geologică a Deltei Dunării. St. tehn. econ., E 16, 161—187, București. — Pricăjan A., Baltac Gh. (1961) Transgresiunile cuaternare ale Mării Negre pe teritoriul Deltei Dunării. St. cerc, geol., 6, 4, 734—762, București. Mihăilescu N., Banu A. (1957) Privire geografică asupra Deltei Dunării. Hidro- logie, I, 215—222, București. Mihăilescu N„ S. Rădan, M. Bleahu, V. losof, R. Giușcă, I. Vanghele (1974) Studiul complex al Deltei Dunării. Study, archives of the Instituie of Geology and Geophysics, București. Mihăilescu N. (1984) Bacurile Matișa și Merhei : structura fundamentului, sedi- mente, condiții de sedimentare (Delta Dunări). Peuce, Tulcea. Murgoci G, (1912) Studii de geografie fizică în Dobrogea de nord. Bul. Soc. rom. geogr., XXXIII, 161—200, București. Mutihac V., Bandrabur T. (1967) Note explicative pour la Carte geologique de Roumanie, Sulina 1 :200 000, Inst. geol., București. Panin N. (1974) Evoluția Deltei Dunării în timpul Holocenului. St. tehn. econ., H/5, 107—121, București. Panin N. (1976) Some Aspects of Fluvial and Marine Processes in Danube Delta. An. Inst. geol. geofiz., L, 149—166, București. Petrescu I. Gh. (1957) Delta Dunării — Geneză și evoluție. Ed. științifică, 232 p.. București. Vâlsan G. (1934) Nouvelle hypothese sur le Delta du Danube. C. R. Congr. Intern. Geogr., II, Varsowie. Institutul Geological României Institutul Geological României N. MIHĂILESCU, C- ROGOJINA. A Fluvial Sedimentation Model-Danube Delta Imprim Atel Inst Geol.Geof ANUARUL INSTITUTULUI DE GEOLOGIE Șl GEOFIZICĂ, VOL. LXIV Redactori responsabili : M. SANDULESCU, G. UDUBAȘA Redactor : I. SANDU Traduceri : A. NASTASE, R. NEGREA, R. LUPAN, M. TOPOR Ilustrația : V. NIȚU Dai la cules : iunie 1984. Bun de tipar : iulie 1984. Tiraj : 750 ex. Hirtie scris 1 A. Format 70 X 100 56 g. Coli de tipar : 30. Comanda 667. Pentru biblioteci indicele de clasificare 55 (058). întreprinderea poligrafică „Informația", str. Brezoianu nr. 23—25, București — România Institutul Geological Românie Institutul Geological României Institutul Geological României Institutul Geological României L'Annuaire de I'Institut de Geologie et de Geophysique a ete public le long des annees sous les titres suivants: ' Anuarul Institutului Geologic al României, t. I-XV (1908-1930) Anuarul Institutului Geologic al României (Annuaire de l'ln~ stitut Gdologique de Roumanie) t. XVI-XX11 (1931-1943) Anuarul Comitetului Geologic (Annuaire du Comite Geologi- que) t. XXIII -XXXIV (1950-1964) Anuarul Comitetului de Stat al Geologiei (Annuaire du Co- mite d'Etât pour la Geologie) t. XXXV-XXXVII (1966 -1969) Anuarul Institutului Geologic (Annuaire de llnstitut G6o - logique ).t. XXXV11I-XLI.I (1970-1974) Anuarul Institutului de Geologie și Geofizica (Annuaire de l’Institut de Ge'oiogie et de Geophysique) depuis le voi XLIII-1975 Institutul Geological României MINISTERE DE LA GEOLOGIE INSTITUT DE GEOLOGIE ET DE GEOPHYSIQUE TOME LXIV Volume special, 6dit6 a Toccasion du 27e . ■ , A'- CONGRES GEOLOGIQUE INTERNATIONAL MOSCOU 1984