BUCUREȘTI 1973 Institutul Geologic al României Institutul Geological României Institutul Geological României Institutul Geological României I NSTITUTUL GEOLOGIC ANUARUL INSTITUTULUI GEOLOGIC VOL. XLI VULCANISMUL NEOGEN AL LANȚULUI MUNTOS CĂLIMANI-GURGHIU-HARGHITA Volum editat eu ocazia SIMPOZIONULUI INTERNAȚIONAL DE VULCANOLOGIE Septembrie 1973 BUCUREȘTI 1973 Institutul Geological României Institutul Geologic al României CONTENT Page D. P. Rădulescu. Position of the Călimani —Gurghiu —Harghita Area within the Neozoic Volcanic Zone of the Alpine Regions....................... 7 D. P. Rădulescu, S. Peltz, A. P o p e s c u. Lower Compartment of the Structure of the Călimani, Gurghiu and Harghita Mountains : The Volcano-Sedimentary Formation.........................................15 S. Peltz, Anca Tănăsescu, I. T i e p a c, Eleonora Vîjdea. Geochemistry of U, Th, K in Volcanic Rocks from the Călimani— Gurghiu —Harghita and Perșani Mountains.........................27 D. P. R ă d u 1 e s c u, Al. D i m i t r i u. Considerations on the Evolution of Magmas during the Neogene Volcanism in the Călimani, Gurghiu and Harghita Mountains....................................................49 D. P. R â d u 1 e s c u. Considerations on the Origin of Magmas of the Neozoic Subsequent Volcanism in the East Carpathians..........................69 D. P. Rădulescu. Tentative Paieogeographical Reconstitution of the Căli- mani—Gurghiu—Harghita Area during the Neozoic Volcanic Activity. . . 77 4 M Institutul Geologic al României \ IGR/ Institutul Geological României POSITION OF THE CĂLIMANI—GURGHIU—HARGHITA AREA WITHIN THE NEOZOIC VOLCANIC ZONE OF THE ALPINE REGIONS BY DAN P. RĂDULESCU1 The northern and. eastern border of the Pannonian Basin — with its eastern extension the Transylvanian Basin — was during the Neogene time the scene where ample volcanic phenomena have occurred (to a much lesser extent they have also taken place either in other regions of this basin or in previous moments). The străin developed in these contact regions between the rigid block from the basement of the basin and the folded or in the course of folding parts of the alpine orogene — which closely joined with the rigid block, — had determined the occurrence of a large zone of weakness along which magmas have migrated toward the surface. The volcanism has developed either on the continent or frequently at the periphery of the basin, where it generated severa! islands, which later attached themselves to land. The Călimani-Gurghiu-Harghita Mountain Chain represents the south-eastern outermost part of this large volcanic region, which practi- cally extends, without any interruption, up to north of Budapest, through the sub-Carpathian Ukraine, Czechoslovakia and Hungary. Although this chain belongs to a clearly outlined petrological province, its various parts display numerous distinctive features; most of them derive from differences relating to the start moment and the duration of the period of the volcanic activity. Age. Nowadays the concept on the migration of the Neozoic volca- nism broadly from west and north towards east and south-east (K u t- h a n, 1948 ; K ă du 1 e s cu, in prinț) is sufficiently argued. From 1 Facultatea de Geologie—Geografie, Bd. Bălccscu, 1, București. 8 DAN RADULESCU 2 this point of view it may be observed that the Călimani-Gurghiu- Harghita Mountain Chain comprises besides older products the most recent ones and the best preserved volcanic structures; these two features cannot be compared to those in other districts of the volcanic region. If our Information about the upper limit of the volcanic period is somewhat more ample, numerous most essential elements concerning the beginning of the activity are as yet but incompletly known. At present it is out of question to establish with precision the relationships between the volcanism of the Călimani-Gurghiu-Harghita area and the tuff horizons both of the Pannonian Basin and the Dacic—Euxinic Basin; this accounts for the fact that the researches were ahso directed towards the sedimentary deposits from adjacent areas. The study carried out by Popescu on the Pannonian deposits along the eastern margin of the Transylvania Depression, in the close neighbourhood of the moun- tain range, has proved that volcanic pyro- or epiclastic elements are occuring in sedimentary rocks hardly in the terminal part of the Panno- nian s.s. (Meotian) 2. It is of interest to point out that the lack of epiclastic volcanic particles in the rest of Pannonian deposits excludes the alterna- tive implying that the corresponding time should represent a calm interval between the periods of volcanic activity. The existence of volcano-sedi- mentary deposits, which form a lower compartment below the one built up of the nowadays conspicuous volcanic super-struetures, proves that the erosion of some volcanic formations when it occurred was imme- diately recorded in the sediments of neighbouring areas. However, if we would admit that an older volcanism had also existed, it is to be situated much lower on the stratigraphic scale, at least, before the Sarmatian in order to explain the total disappearance of the volcanogenous material until the beginning of the Pannonian; as we have to deal with a small-sized basin we would rather expect, a preser- vation of such a material in sediments during a longer time interval, than its rapid disappearance. A volcanism so old would not represent, however, but another „stage” of the one under discussion; it would be something different, and its correlation with the* already identified volcanism, and that from the neighbouring areas, is to be examined under other angles. 2 A. Popescu (1966) Studiul mineralelor grele din depozitele pannoniene situate între valea Mureșului și valea Gurghiului. Manuscript. Arh. Inst. Geol. Likewise subsequent manuscripts. 'JA Institutul Geological României 16 R/ 3 THE CALIMANI-GURGHIU-HARGHITA AREA WITHIN THE ALPINE REGIONS 9' The eontinuance of the volcanic activity until very recent moments was suggested by numerous researchers relying on the good preservation of volcanic apparata (Eădulescu et al., 1964), as well as on the Identification, either in drillings or at the surface of some horizons of volcanic material intercalated in Quaternary deposits (P r i c ă j a n, 1961; L i t e a n u, M i h ă i 1 ă, B a n d r a b u r, 1962 ; Gh e n e a, 1967); these observations have determined some scientists to accept the eontinuance of volcanism up to, at least, the Middle Pleistocene (Liteanu, Ghenea, 1966; Peltz 1971). The absolute age determinations carried out these last years (E ă d u- lescu, Pătraș cu, B e 11 o n, 1972) allowed to make some essential specifications, without- exhausting this problem (Eădulescu, in prinț). The age of 3.92 x IO6 years for rocks, which closed the volcanic activity in the largest part of the Harghita Mts, renders mostly impro- bable if not completely excluded a much younger volcanic activity. On the other hand, the ages of 7.08 and 7.37 x 10 6 years, for older rocks, also pertaining to the upper compartment of the volcanic structure, are in perfect agreement with the beginning of the volcanic activity in the terminal part of the Pannonian (= basis of the Pliocene at about 12 x IO6) years. Another fundamental concept documented by absolute ages is that the migration of volcanism may be recognized even within the Călimani- Gurghiu-Harghita area, where both the beginning and the closing of volcanic phenomena have succeded from north towards south (E ă d u- 1 e s c u in prinț). The conclusion which has therefore compelled the recognition is as follows : the whole volcanic activity from the Călimani-Gurghiu- Harghita area, whose products are today conspicuous, is very young and represents the terminal part of the subsequent alpine magmatic activity. Released material. Both the late moment of starting of volcanism and its shorter displaying period had profound repercussion as regards the nature of the material having been expelled. By contrast with all other areas of the alpine region showing subsequent Neozoic volcanism — wherein the petrographical and Chemical variety displays in most cases a wide range — within the Călimani-Gurghiu-Harghita area only ande- sitic magmas closely related as to their Chemical features, were released. The totality of products has a pronounced basic character, preserved during the whole activity; the quartz-bearing forms of andesites and Institutul Geologic al României 10 DAN RĂDULESCU 4 the dacites are recognized only incidentally and their spreading is very limited. As it may be observed the normal and complete development of processes during the subsequent volcanism — alternation of andesitic and rhyolitic + dacitic stages — cannot be recognized in this area. As regards some areas, e.g. the. Apuseni Mountains or the Oaș-Gutăi area, the difference consists only in the lack of this alternation, fact which would eventually allow to presume that in the Călimani-Gurghiu-Harghita area it is only the last andesitic phase that is represented (the difficulties as to accept such a hypothesis have been, however, mentioned); with respect to other areas, such as central Slovakia, the difference consists in the nature itself of the last phase, which is there a rhyolitic one (F orga c et al., 1968). This remarkable pctrographical and Chemical uniformity of the volcanic material may have been mostly originated by the type of the differentiation magmatic processes maybe due to their short time of development, which did not essentially affect, the primary features or magmas; nevertheless the homogeneity of magmas, correlated with the immense bulks of rocks they have built up, does not fail to suggest theiv deep-seated origin. Volcanic activity. The Chemical nature of magmas has determined the general type of the volcanic activity. As compared to other areas, the clear-cut separation in time of the dominantly explosive activity from that with a dominantly effusive character, proves to be specific here; the last part of the activity (upper compartment) is practically lacking on pyroclastics, whereas in the first part (lower compartment) and in the sedimentary deposits of corresponding age from adjacent regions, they are very well represented. Although the type of the mixed activity and that of the stratovolcanic structure is still characteristic of the Călimani-Gurghiu-Harghita area, nevertheless it marks a rather obvious individualization as compared to other areas, especially for the last moment of the volcanism from this area, the upper compartment. The very rapid rhythm of the development of phenomena is like- wise characteristic; the building up of the volcanic structures and their destruction during the first stage, as well as the building up of volcanic edifices during the second stage of activity corresponds to relatively short time intervals. From this viewpoint both stages of volcanic activity Institutul Geological României 5 THE CALIMANI-GURGHIU-HARGHITA AREA WITHIN THE ALPINE REGIONS H over the Călimani-Gurghiu-Harghita area represent, in comparison with other areas, only two isolated although very strong paroxysmal manifestations. In the light of the so far expounded ideas relating to the nature of the released material, as well as to the development of the volcanic activity, the hypothesis about the relations between the volcanism of the Călimani-Gurghiu-Harghita area and the formation of the tuff horizons from neighbouring regions, appears more clearly. As previousley noticed, this problem cannot be rised, but only beginning with the Upper Pannonian s.s. deposits. Or, very significant is the fact that by contrast with the frequency and thickness of the tuffs in the pre-Pannonian depo- sits, in deposits Pannonian in age the tuffs occur but exceptionally always bearing an andesitic character and of reduced thickness, and only in the outer part of the Carpathian Arc; more frequently the pyro- clastic material occurs as associated with the epiclastic one in hybrid rocks. This situation is quite corresponding with the features of volcanism so as they were sketched for the Călimani-Gurghiu-Harghita area : namely exclusively andesitic, and consisting of two distinct moments of activity, the first predominantly explosive, and the second predomi- nantly effusive. Basement. The basement of the Călimani-Gurghiu-Harghita area is characterized by the existence, at rather small depths, of metamorphic rocks. Excepting the Southern outermost part — where the presence in depth of Mesozoic deposits showing a large thickness and pertaining to the folded structure of the Carpathians — within the whole area, the metamorphic massif is overlain only by Neogene deposits, and to a lesser cxtent, by the Paleogene ones; their thickness is variăble east-westwards occasionally reaching 1500 m. This situation is, if excepting some isolated points from the Apuseni Mountains and from the area with subvolcanic structures of the East Carpathians, absolutely uncommon within the region showing a subsequent Neozoic volcanism, and its repercussion on the development of phenomena must not be overlooked. It is most probable, for instance, that the purity of andesitic magmas and the homogeneity of their features could be partly at least explained by the insignificant thickness of the sedimentary deposits pierced during their ascent; on the other hand, the same argument points out, as mostly presumable, the fact that the volcanic products forming the Southern outermost part of the Harghita Mts area should have been submitted Institutul Geologic al României IGR/ 12 DAN RADULESCU 6 to influences due to the sedimentary basement they pierced. Differences of this nature which have been discerned between the volcanic rocks from the Southern part of this area and the rocks from the median and the northern ones have confirmed this hypothesis (Eădulescu, D i m i t r i u, this volume). From the structural point of view it is noteworthy that the area, where the volcanic activity took place tallies partially with a presumable deep-seated dislocation line, along which basaltic magmas have subse- quently achieved the piercements of the basement (Eădulescu, 1962). This fact has certainly contributed to the „fixation” of volcanism within a very narrow surface of a linear character. In most other areas the position of volcanic edifices seems to have been controlled by complex Systems of direcțional and transversal dislocations that make the distri- bution of volcanic apparata rather complicated and variable. Within the Călimani-Gurghiu-Harghita area the distribution of volcanic edifices is almost perfectly linear. Obviously we are not dealing with a single dislocation but probably with several dislocations disposed ,,en coulisse”, hence both the parallelism and the very reduced distance between them contribute to give a general impression of „liniarity” over the whole zone. Although this aspect is determined by the distribution of apparata from the upper compartment of the structure, it is probable that also the previous edifices corresponding to the lower compartment — volcano- sedimentary formation — had a similar position since none indications related to the presence of some roots of volcanoes outside the axial zone from this area do exist. Age, released material, type of activity, basement traversed — there are the chief factors owing to which the Călimani-Gurghiu- Harghita area marks its individualization as compared to other areas with subsequent Neozoic volcanism, along the Alpine-Carpathian Range; they have determined the distinct petrographic, structural, paleogeo- graphic features, permitting to consider the Călimani-Gurghiu-Harghita Mountain Chain as a perfectly outlined geological-volcanic unit in this province. The succint analysis carried out here elucidates, however, the approach of the very frequently discussed problem referring to the correlation of areas with subsequent volcanism over the territory of Romania or over the whole Alpine-Carpathian territory. In our opinion Institutul Geologic al României 7 THE CĂIjTMANI-GURGHIU-HARGHTTA AREA WITHIN THE ALPINE REGIONS 13 within the Călimani-Gurghiu-Harghita area there exist distinctive features even in essential characters of volcanic and geological pheno- mena, which allow correlations only at a general level. In spițe of the desiderata and attempts of the author himself to find terms which would correspond as to time, volcanic activity type, petrographical, Chemical, metallogenetic features foi’ various areas, we had to reach the conclusion that for the Călimani-Gurghiu-Harghita area its appurtenance to the province of the subsequent Neozoic volcanism is solely reflected in its lessentia features upon which numerous peculiar elements have grafted. REFERENCES F o r g â 5 I., K a r o 1 u s K., K a r o 1 u s o v â E., K o n e c n y V., K u t h a n M. (1968) Subsequent and Final Volcanism in the West Carpathians (Central-Slovakian Region). Intern. Geol. Congr. 23^ Sess. Proceed. Seci. 2, Volcanism and Tectogenesis, Prague. Ghenea C. (1967) Prezența unui tuf vulcanic în Villafranchianul din Depresiunea valahă. Inst. geol., St. tehn. econ., H, 3, București. Kuthan M. (1948) Undacny Vulkanizmus Karpatsk^ho Orogenu a Vulkanologick6 Studia v Sev. Casti Presovăkych Hâr. Prâce St. Geol. Ost. Bratislave, SoSit 17, Bratislava. Litcanu E., Ghenea C. (1966) Cuaternarul din România. Inst. Geol., St. tehn. econ., II, 1, București. — M i h ă i 1 ă N., Bandrabur T. (1962) Contribuții la studiul stratigrafiei Cuater- narului din bazinul mijlociu al Oltului (Baz. Baraolt). Acad. R.P.R., St. cerc, geol., VIII, 4, București. Peltz S. (1971) Contribuții la cunoașterea formațiunii vulcanogen-sedimentare pleistocene din sudul munților Harghita și nord-estul bazinului Baraolt. D. S. Inst. geol., LVII/5, București. P r i c ă j a n A. (1961) Cercetări hidrogeologice în ținutul de cîmpie dintre Buzău și Ialomița Inst. geol., St. tehn. econ., E, 5, București. Rădulescu D. (1962) Probleme ale vulcanismului terțiar din munții Călimani, Gurghiu și Harghita. Acad. R.P.R., St. cerc, geol., VII, 2, București. — (1969) Ober die Anwesenheit einer Tiefenbruchzone entlang dem 25° 30' ostlichen Meri- dian, zwischen 42° und 47° nordlicher Breite, Rumănien. Geol. Rundsch., 59., 1, Stuttgart. — (in prinț) Considerații asupra cronologiei proceselor vulcanice neogene din Munții Călimani, Gurghiu și Harghita. D. S. Inst. Geol. LIX/4 (1972). București. — Vasilescu Al., Peltz S., Peltz Margareta (1964). Contribuții la cunoaș- terea structurii geologice a munților Gurghiu. An. Com. Geol., XXXIII, București. — B o r c o ș M. (1968) Aperțu general sur l’ăvolution du volcanisme nfiogene en Roumanie. Ann. Com. Geol., XXXVI, Bucarest. Institutul Geological României 14 DAN RĂDULESCU 8 — Pătrașcu St., Bellon H. (1972) Pliocene Geomagnetic Epochs : New Evidence of Reversed Polarity around the Age of 7 my. Earth a. Planet. Sci. Letters, 14, 1 Amsterdam. — Dimitri u Al. (1973) Considerations on the Evolution of Magmas during the Neogene Volcanism in the Călimani, Gurghiu and Harghita Mts. (this volume). București. Slavik J., Danilovich L. G., Cvercko J., Rudinec R. (1968) Tectonics and Subsequent Volcanism in the Western Part of East Carpathians. Intern. Geol. Congr. 23d Sess. Proceed. Seci. 2, Volcanism and Tectogenesis, Prague. LOWER COMPARTMENT OF THE STRUCTURE OF THE CĂLTMANT, GURGHIU AND HARGHITA MOUNTAINS : THE VOLCANO-SEDI- MENTARY FORMATION BY DAN P. RĂDULESCU.1, SERGIU PELTZ2, ANTON POPESCU2 The basal part of the volcanic structure from the Călimani, Gurghiu and Harghita Mountain Chain represents an independent compartment — a very complex volcano-sedimentary formation — which crops out particularly in the peripheral zones of the region (Rădulescu et al. 1964); in proportion of about 45 per cent this compartment is overlain by the upper compartment of the structure — volcanic apparata with lavas and, subordinately, pyroclastics. The maximum extension east- westwards of the lower compartment is reached in the central and Sout- hern parts of the Gurghiu Mts (about 40 km). Its thickness of order of hundred metres, is variable and ranges most frequently from 300 to 500 m. The basement overlain by the lower compartment is built up of sedimentary deposits, Tortonian, Buglowian (uncertain) Sarmatian and Pannonian s.s. in age. Among these deposits only the Sarmatian, and especially the Pannonian ones, are of interest as to their extension and possibilities as to have supplied elastic material for the volcano-sedimen- tary formation. The Sarmatian has developed in the molasse facies and is slightly fossiliferous. It consists of a conglomeratic horizon (lower ) and a marly horizon (upper). The Pannonian oceurs transgressively and unconformably over Sarmatian deposits, and is characterized by its lithological uniformity : 1 Facultatea de Geologie—Geografie, Bd. Bălcescu, 1, București. 2 Institutul geologic, Șos. Kiseleff, 55, București. JA Institutul Geological României IGRZ 16 DAN RĂDULESCU et al. 2 grey marly clays within which sand or rarely gravei intercalations more or less Consolidated do occur. Broadly three horizons —namely the lower clayey horizon, the median sandy horizon and the upper clayey horizon — whose cartographical separation presents some difficulties may be recog- nized ; their thickness reaches approximately 1500 m. The most extended is the upper clayey horizon both as to its area and its thickness in the stratigraphical column (about 1000 m). In this prevailingly clayey packet frequent intercalations of grey fine sands, sandy clays, as well as coal seams of infinitesimal thickness are encountered. The sandy horizon is well developed on the western slope of the Gurghiu Mts where it reaches a thickness of 250—500 m. Southwards, on the western slope of the Harghita, the sandy and upper clayey horizons are replaced by a conglomeratic horizon of about 700 m thick with frequent, however, obviously subordinated intercalations of clays, sands and sandstones. The Volcano-Sedimentary Formation Terrigenous and volcanic rocks differing as regards their grain size, facies, petrographic type take part in the building up of the volcano-sedimentary formation. The andesite material builds up the background of the formation, the participation of the nonvolcanic one ranging commonly from 5 to 10 per cent. The pctrographical components of the volcano-sedimentary forma- tion fall into three basal categories : non-volcanic, volcanic and hybrid; neither the presence of the three categories of rocks, nor the presenee of all petrographic types from each category are absolutely necessary; the volcano-sedimentary formations display various aspects according to the association mode of these components. In the figure 1 an attempt to systematize these possibilities on purpose to achieve a most exact description and definition of various situations is presented. The convențional notation of petrographic com- ponents leads to synthetic descriptive forinulae which contain qualita- tively the specific features of the formations. The so far carried ont researches have evidenced the fact that within various regions of the Călimani-Gurghiu and Harghita Mts, the petrographical components of the formations develop in a diffe- rential mode, without, however, to give rise to essential differences between the three parts of this chain. Our present knowledge of the volcano- sedimentary formation allows to distinguish within it three sequences with regional extension. The composition of the formation is schema- L- Institutul Geologic al României 3 THE VODCANO-SEDIMENTA1RY FORMATION tically rendered in the lithological columns of the figure 2, particularly according to the situation in the western part of the eruptive chain, where the most frequent outcrops are encountered. The petrographical classifi- cation and nomenclature used here are presented in the table. Fig. 1. — Constituents of the volcano-sedimentary formation from the Călimani, Gurghiu and Harghita Mts. a, b, c mark successively the coarse, median and fine grain-size. TABLE Terminology utilized for petrographic types Grain-size mm Non-volcanic Hybrid Volcanic Pyroclastic Epiclastic Over 100 Conglomerate Breccia, hybrid conglomerate Pyroclastic breccia Volcanic conglo- merate 32-100 Microconglome- rate Microbreccia, hybrid microconglome- rate Pyroclastic micro- breccia Volcanic micro- conglomerate 0.1-32 4-32 Sandstone Hybrid sandstone, tuffite Lapilli tuff Volcanic sandstone 1-4 Coarse ash tuff 0.1-1 Fine ash tuff Under 0.1 Pelite Dust tuff Volcanic pelite 2 — c. 6S0 18 DAN RADULESCU et al. 4 The lower sequence comprises products of the first volcanic manifesta- tion from the region, and epiclastic deposits wherein volcanic compo- nents 3 appeared for the first time. Its thickness ranges from 30 to 100 m. The deposits are conspicuously exposed at the periphery of the volcanic zone, especially in the neighbourhood of Sovata, Ocna, Păuleni, Deda, Eăstolița and in the Gurghiu Valley, where the relationships between the underlying sedimentary deposits, and those with which the volcano- sedimentary formation begins, could be minutely established. Along the western border of the volcanic chain, the transition from the clayey-detrital Pannonian deposits, completely devoid of volcanic components (C/D Zone) to the volcano-sedimentary ones was progressi- vely achieved, through a reddish sandy packet, guide horizon, at whose level the first indices of the Neogene volcanic activity from this sector of the East Carpathians were identified. Extending over a length which exceeds 150 km „the red sand horizon” is composed of yellow-reddish fine-grained (median diameter 0.12—15 mm) sands, whose thickness varies between 5 and 25 m. In the heavy fraction of these sands, repre- senting less than 1 per cent of the whole arenaceous material, the amounts of volcanic minerals, mainly hypersthene and green hornblende, are ranging from 0.5 to 45 per cent. Their quantitative and qualitative variation is presumably reflecting the existence of several volcanic edi- fices, which have supplied with ash material. The participation of the volcanic component is usually discernible only by means of a microsco- pical examination ; it is represented not only by heavy fraction particles but also by iron from the hydroxides which give its colour to the deposit. Alternations of epiclastic and pyroclastic deposits are less frequently encountered (Hodac, along the Gurghiu Valley). Due to the faunal assemblage existing at the level of red sands {Congeria subglobosa Partsch and Unionides with a robust Shell) these deposits are referable to the basal part of the E Zone of the Pannonian, thus the moment marking the beginning of the volcanic activity in the Călimani-Gurghiu-Harghita Chain corresponds to the transition from the C/D Zone (clayey-detrital Pannonian, fauna with Congeria banatica E. H o e r n.) to the E Zone (volcano-sedimentary Pannonian, fauna with Congeria subglobosa Partsch). 3 A. Popescu (1966). Studiul mineralelor grele din depozitele pannoniene situate Intre valea Mureșului și valea Gurghiului. Manuscript Arh. Inst. Geol. A. Popescu (1968). Studii sedimentologice asupra depozitelor pannoniene de pe versantul vestic al munților Gurghiu, Manuscript Arh. Inst. Geol. 'A Institutul Geologic al României IGR/ THE VOUCANO-SEDTMENTARY FORMATION 19 ABC Fig. 2. — Synthetical lithological columns in tlie volcano-sedimentary formation. j. North-western part of the Călimani Mts (Peltz, 1965, unpublished data). B. Mureș Defile Zone (Peltz and Peltz, 1963, unpublished data; Rădulescu et al.. 1964; Peltz, 1965. 1969). C. South-western part of the Gurghiu Mts (Peltz and Peltz, 1970). I lower sequence; II intermediar? sequence; III upper sequence. 1, marls, eandy mărie, clays; 2, hybrid agglomerates; 3. epiclastics. 4, 5, 6, 9. 10, pyroclastic breccia, pyro- clastic microbreccia, tuffs; 7, basalt andesite; 8. andesite. Institutul Geological României 20 DAN RĂDUEESCU et aa. 6 The red sands are often overlain by grey compact slightly marly clays, devoid of arenaceous intercalations, 4—12 m thick, wherein the content of volcanic minerals is, likewise considerably increased. The development of these clays proves to be discontinuous, frequently reduced to the order of decimetres, or even centimetres at the uppermost part of the red sands. In these upper clays scarce and weakly preserved forms, pertaining to the fauna with Congeria banatica R. H o e r n. ascertain the persistence of this form up to the level of the fauna with Congeria subglobosa P a r t s c h. Deposits which are directly overlying the red sands or the clays are slightly different from one point to another. Usually there is a pyro- clastic and epiclastics alternation with fragments of 4—12 cm in diameter, accumulated under subaquatic conditions. The non-volcanic material is subordinate; the andesitic epiclastics amount, however, about 10 per cent even in rocks with aspect of volcanic breccia. From the point of view of grain size and shape of the fragments, the rocks are homo- geneous; they frequently present a bedding, and an advanced alteration degree of the tuffaceous binding. In other cases epiclastic horizons are absent the material of this nature occurring subordinately in hybrid rocks. An alternation of microconglomerates, breccias, pyroclastic breccias and microbreccias, tuffs, hybrid conglomerates and sandstones, tuffites is deposited in continuity of sedimentation. Within the hybrid rocks the predominance of volcanic minerals is evident, however, contents of 5—10 per cent of metamorphic minerals (almandine, zoisite, clinozoisite, epidote, zircon) are also characteristic. Such deposits were generated under subaquatic conditions. At the terminal part of the sequence coarse pyroclastics with small-sized intercalations of tuffs or epiclastics are recognized. From the point of view of their petrographic nature, volcanic fragments of the lower sequence are hornblende (green or brown) -ande- sites and different varieties of pyroxene- and hornblende-bearing andesites. The main features of the lower sequence seem to be as follows : a) heterogeneous constitution determined by the association ofthe volcanic material (pyroclastic and epiclastic) with the non-volcanic one; b) wide developement of the subaquatic facies; c) strongly explosive nature of the volcanic activity supplying material; d) lack of lava flows and intrusive bodies. According to the codification presented in the figure 1, the variety of rocks that enters into the composition of the sequence, may be expressed as follows (the frame around some notations indicates Institutul Geologic al României 7 THE VOIJCANO-SEOIMENTAKY FORMATION 21 a subaquatic sedimentation; when materials with different grain size do coexist, the dominant size class is noted at the numerator) : 2a 2b la 1b 1 0c 1 4b 1— b li c 6b The intermediary sequence presents a more complex lithology than the lower one. Lava flows and intrusive bodies, always of andesitic nature, are to be found together with pyroclastics and epiclastics; there are absent rocks built up exclusively of nonvolcanic components showing in general a very strictly localized distribution. The thickness of the sequence ranges — as it may be stated in the south-western part of the Gurghiu Mts and in the Mureș Defile—from 250 to 400 m. In the north-western part of the Călimani Mts the intermediary sequence is not sufficiently individualized. The deposits which may be referred to it are pyroclastic breccias and microbreccias with elements of pyroxene-andesites and pyroxene-hornblende-bearing andesites, com- prising intercalations with epiclastics showing the same lithological com- position. In the Mureș Defile Zone (Southern part of the Călimani Mts and the northern one of the Gurghiu Mts), the intermediary sequence is very well developed (fig. 2, B). In the lower third of the sequence, breccias and pyroclastic microbreccias with intercalations of tuffs and epiclastics are encountered. Fragments of all deposits belong to pyroxene andesites, and subordinately to hornblende- pyroxene-bearing andesites. This complex contains flows of basaltic andesites. In this part of the sequence the subaquatic facies predominates too as in the lower sequence. The subordinate participation of lavas points out that the volcanic processes, contemporaneous with the building up of this part of the formation, have been predominantly explosive; the petrographic features of lavas indicate a subaerial volcanism. An important moment in the lithogenesis of the intermediary sequence from this territory is marked by the activity of lacustrine basins, namely Andreneasa, Lunca Bradului, Neagra and Toplița located DAN RĂDULESCU et al. within inner depressions of the mountain chain. In these basins, deposits showing the same volcano-sedimentary features, have accumulated. The most characteristic development of these complexes may be observed in the central part of the Toplița Basin, where alternations of conglome- rates, microconglomerates, sands, sandstones, and subordinately clays with coarse and fine pyroclastics, are encountered. The deposits are characterized by a normal rhythmic bedding or, occasionally a crossed one, the variety of grain size and mineralogica! composition. In epiclastic deposits rests of ligneous vegetation or of the herbaceous one, that have undergone the incarbonization or opalization processes are found. The constituent fragments of deposits are hornblende-andesites, and subordi- nately pyroxene-hornblende-bearing andesites or pyroxene-andesites. The deposits of these basins reflect locally a quiet period of the volcanic activity without, however, its complete ceasing. In the synthetical column of the formation from the Mureș Defile Zone (fig. 2, B) the deposits of these basins are „symbolically” represented by epiclastics since the latter constituie the type of the predominant rock. At the upper part of the sequence breccias and microbreccias, tuffs with intercalations of epiclastics and andesitic lavas do reappear. In the Southern part of the Gurghiu Mts, the basement uf the intermediary sequence —consisting likewise of an alternation of pyroclas- tics and epiclastics with fragments of similar petrographic nature, com- prising andesitic lavas — presents clear-cut features of subaquatic deposi- tion ; by contrast, the upper part was predominantly subaerially accumu- lated. Conglomerates and microconglomerates from the lower part of the sequence are composed here of boulders and well-rounded pebbles. In the constitution of rocks from the lower part of the sequence there participated 70 per cent of volcanic material — of the same nature as in the rest of the region — and 30 per cent of pebbles of black quart- zites, white quartzites, gneisses etc. The matrix of conglomerates is porous, occasionally friable, grey-yellowish displaying a variable grain- size. Sandstones consisting exclusively of volcanic material, often with impressions of plants are added to coarse rocks. The pyroclastics are well represented both in the basal part and in the upper one of the sequence by rocks showing all types of grain-size. The intermediary sequence may be characterized as follows : a) a subordinate and very limited participation of nonvolcanic components; b) an important participation of epiclastic deposits; c) a wide develop- nstitutul Geological României 9 THE VOLCANO-SEJDIMENTAR-Y FORMATION 23 ment of the subaquatic facies; d) the presence of andesitic lavas. Its composition may be expressed by the formulation : la lb UM | 4a |_____3a I 3a I l~3b| I 3c | 7 The upper sequence presents a lithology perfectly correlable over the whole territory of the volcanic Chain. This situationis schematically illustrated in the synthetical lithological columns of the figure 2. Broadly, the upper sequence is composed of pyroclastic breccias and microbreccias and tuffs which alternate, and to which lavas and intrusive andesitic bodies are added. The constituent elements of the elastic rocks are horn- blende-andesites, pyroxene-hornblende-andesites and basaltic andesites. Fragmente occasionally reaching considerable sizes with angular and subangular shapes are encompassed within a grey compact or porous matrix either microbreccious, lapillic or tuffaceous. The thickness of the sequence reaches sometimes 300—400 m. The chief features of the upper sequence are : a) relatively simple petrographic composition; b) the accumulation of material exclusively under subaerial conditions; c) rised frequence of lava flows and intrusive bodies; d) quite subordinate occurrence of epiclastic components. Its codified expression is : la lb 3b 7 The present phase of knowledge relating to the volcano-sedimentary formation does not allow to determine with precision the upper limit of the terminal sequence. It is quite possible that the pyroclastics which were included at the upper part of this sequence, would represent the beginning of the Institutul Geological României 24 DAN RĂDULESCU e basaltic andesites, andesites from the Hnd stage being more radioactive ; b) differences between the radioactivity of hornblende and pyroxene-bea- ring andesites from the Gurghiu Mts and the same andesites from the Călimani-Harghita Mts; c) along the whole volcanic chain the radioacti- /A Institutul Geological României IGR/ 21 G-EOCHEMISTRV OF U, TH, K, IN THE EASTEIRN CARPATHIANS’ VOLCANIC ROCKS 47 vity increase north-southwards, the Harghita andesites being richer in Th, U, K than those from Gurghiu and Călimani. From these the most radioactive are the biotite-andesites ; it is probable that the enrichment in U and Th might be explained by a pneumatolytic differentiation during the evolution of the magma; d) the cement of volcano-clastics presents contents of U lower than those of lava fragments, whereas an accumula- tion of U and Th in fine-grained epiclasticis noted (Toplița). Andesites from the Călimani-Gurghiu Mts present average contents of U and Th similar to those of andesites of USSR and USA. It may be concluded that differences between the radioactivity of basalts, andesites and dacites do exist; over the volcanic area, as whole, a rise of radioactivity from basalts to dacites is observed. The correlation among the U, Th and K distribution and the petro- graphical and volcanological features point out the dependence of the distribution of these elements on the magmatic differentiation processes (which took place during each of the two stages) and on certain peculiar situations namely the case of the biotite-andesites. The study of volcanic products which have undergone secondary alteration processes yields following data : in sectors with fumarolisations the radioactivity is higher for silicified rocks and lower for the argillized ones ; in sectors with hydrothermal alterations, a variation of radioactivity about guide mark values (average content in the fresh-appeared rock) is observed. Increases of the U and Th values occur for more acid rocks such as andesites and amphibolic microdiorites. The results obtained demonstrate the usefulness of radiometric study with a view to complete our knowledge regarding the geochenrstry of neovolcanics and relying on it to proceed to a thorough study of petro- genetic problems. There were likewise obtained indications related to the contribution of the radiometry to detect zones of secondary enrichment, as well as to point out the differences between the fumarolic processes and the hydrothermal ones, fact presenting involvements of metallogene- tical nature. REFEREXCES C h e m i n 6 e L. J., Nor d em an D. (1964) Dosage du K, U, Th, Ra par spectrometrie gamma dans les laves d’Auvergne du Valey et de la province Siciliene. Bull. Soc. Geol. France. V, 2, p. 208—232. Paris Institutul Geological României 48 SERGIU PELTZ et al. 22 — (1969) Distribution de U, Th, et du K dans les laves de Ia Domaklie (Etiopie). C.R. Acad. Sci. D. T. 268 p. 1675-1678. Paris. Heier S. K., Rogers W. J. (1963) Radiometric determination of thorium, uranium and potassiuin in basalts and two magmatic differentiation series. Geochim. et Cosmo- chim. Acta, 27, 2, p. 137—154. London. Loccardi E (1967) Uranium and thorium in the volcanic processes. Bull. Voie. XXXI, p. 235 — 260. Napoli. Imbd G., Gasparini P., Luongo G., Rapolla A. (1968) Contributions to the volcanological researches by determination of the radioactivity of eruptive products. Bull. Voie. XXXII, p. 1-25. Napoli. Peltz S., Vasiliu Cecilia, Bratosin Irina (1971) Petrologia rocilor bazaltice plio- cuaternare din România. An. Inst. geol., 39, București. — Vasiliu Cecilia, Udrescu Constanța, Vasilescu Al. (1973) Geochemistry of volcanic rocks from Călimani, Gurghiu and Harghita Mts. An. Inst. Geol., 42, București. S t u s s i J. M. (1970) Le volcanisme associd au Culm des Vosges Meridionales. Tendances evolutives generales et geochimie de l’Uranium et du Thorium. These Univ. de Nancy. T a y 1 o r S. R. (1965) Trace element chemistry of andesites and associated calc-alkaline rocks. Proc. Andesite Conference, Bull. 65, p. 43 — 63. Oregon. Vinogradov V. V. (1963) Osnovî certî geohimii urana. Moscova, p. 351. Institutul Geological României PARȚIAL HISTOGRAMS S. PELTZ et al., Geochemistry of U,Th, K in volcanic rocks from the Călimani, Gurghiu, Harghita and Perșani Mountoins PLATE I a. Basalts n = 24 d- Hornblende - and pyroxene-bearing andesites n =33 50- 30- 20- 10- 40- 30- 20- 10 - 3,0 5,0 7.0 9,0 rOpp.m 40- 30- 20- 10- 40- 40- 40- 30- 30- 30- 20- 20- I 10- 10- 1O- 0,8 1,3 1,8 2,1 39 4,4 /nppm tfop.m 40 - T b. Basaltic andesites e. Hornblende-bearing andesites n =22 40- 30- 20- io- 40- 30- 20- 10- l/pp.m Thppm C- Pyroxene-bearing andesites n = 63 40- 30- 10- 9 2,2 5,6 10,0 14,3 18,1 (/pp.m rhppm 40- 30- 10- 0,8 1,6 2,3 30- 20- 10- Upp/n 30- 20- 10- Thppm 30- 20- 10- 30- 30- 20- 10- 10 d f. Volcanoclastics n = 43 30- 20- 10- 1,0 4,8 8,0 11,2 ropp.io 1-----------r i------------r l 1-----------r T T i-------------r ANUARUL INSTITUTULUI GEOLOGIC VOL. XLI Imprim. Atei. Inst. Geologic A Institutul Geologic al României IGR/ U VS-TH AND TH/U VS. K IN BASALTS AND ANDESITES S. PELTZ et ol., Geochemistry of U.Th.K in volcanic rocks from the Călimani, Gurghiu, Harghita and Perșani Mountains PLATE II (/p.p.m. Basalts 3 - + O 2 - X ° § X 1 o i ।--------'■ 5 6 7 a a Thp.p.m • Călimani M.ts + Gurghiu M.ts x Harghita M.ts • Compact type + Vacuolar type 0 Scoriae Biotite - bearing andesites Hornblende - and pyroxene-bearing andesites Hornblende - bearing andesites Upp.m 6- Uppm 7 - Sb. 0 o Iu 17)ppm Jnpp.m X X' X i---------f-----------r fO 12 li T 16 • Călimani Mts +■ Gurghiu Mts x Harghita Mts x Călimani Mts Gurghiu Mts Harghita Mts x Harghita Mts ANUARUL INSTITUTULUI GEOLOGIC VOL. XLI Imprim. Atei. Inst. Geologic Institutul Geologic al României CONSIDEEATIONS ON THE EVOLUTION OF MAGMAS DUEING THE NEOGENE VOLCANISM IN THE CĂLIMANI, GUEGHIU AND HARGHITA MTS BY DAN P. RĂDULESCU1 and AL. DIMITRIU2 The Neogene volcanics from the Călimani, Gurghiu and. Harghita Mts are rather well-known from the Chemical point of view, and petro- graphical considerations on this basis either of a regional or general cha- racter were presented in severa! previously published papers (E ădu- 1 e s c u, 1963 ; Eădulescu, Borcoș, 1968 etc.). The massive increase of the Chemical information — as regards both the major com- ponents and, to a less extent, the minor components — allows today a statistical analysis of the petrological hypothesis. The results thus obtained are integrating into the present-day outlooks on the evolution of volcanism from this region; they partly substantiate the already expressed concepts as a result of geological and petrological studies, but they largely represent on the other hand, quite new ideas. Primary information and uscd statistica] methods Our present-day knowledge of the Neogene volcanism from the Călimani, Gurghiu and Harghita Mts does not as yet satisfactorily argue the answers to two fundamental questions : 1. Which are the relationships among the volcanic manifestations of the Călimani, Gurghiu and Harghita areas? 2. Which are the relationships among the evolution stages of volca- nism both within each of the above three areas and also comparatively among them? 1 Facultatea de Geologie—Geografie, Bd. Bălcescu, 1, București. 2 Institutul Geologic, șos. Kiseslef 55, București. 4-0. 630 Institutul Geological României 50 DAN RĂDULESCU, ALEXANDRU DTMITRIU 2 Geological-petrological and volcanological criteria have not only allowed to answer these questions but also to draw a general picture of the geological evolution of this region. However, the answers obtained comprise, besides numerous objective elements, also a large hypothetical part, fact that renders them liable to permanent improvement from the argumentation and interpretation points of view. As the way these two questions may be answered allows to under- stand the evolution of the volcanism in this region, and since they are very well suited to be examined with the aid of Chemical data and by means of statistical methods, we will focus our attention on them. The analytical data are concerning both the contents in major components (SiO2, A12O3, Fe2O3, FeO, CaO, MgO, Na2O, K2O, TiO2, P2O5) (152 samples) and the minor components (Pb, Cu, Zn, Ni, Co, Cr, V) (310 samples); they are mostly supplied by the papers of E ă d ules cu (1961) and Peltz et al.3 As it may be stated from tables 1 and 2, all the petrographical table 1 Relative frequency f% of petrographical types pertaining to the Neozoic volcanism from the Călimani, Gurghiu and Harghita Mountains, studied as for their composition of major Chemical elements* Petrographical type Călimani Gurghiu Harghita I I+II I II I+II I II I+II Dacites Hornblende-andesites 8.8 26.7 11.2 6.4 22.2 28.6 43.9 41.7 29.8 27.9 Hornblende- pyroxenes andesites 2.2 5.6 3.2 14.3 7.3 8.3 37.5 9.6 11.5 Pyroxenes-andesites 24.4 72.2 38.1 42.9 43.9 43.7 50.0 57.0 56.6 Basaltic andesites Diorites, microdiorites Gabbros, microgabbros 35.6 2.2 5.6 5.6 25.4 1.6 3.2 12.5 0.8 * In all Tables, the two volcanic stages from each region are noted with I and II constituents of the region under investigation are satisfactorily represen- ted in the analysed material. Our discussion is relying on fundamental data resulting from the geological research, particularly (a) on the sepa- 3 P e 11 z S., V a s i 1 e s c u Al., Vasiliu Cecilia, U d r e s c u Constanța (1969). Corelarea formațiunilor eruptive masive din lanțul Călimani—Gurghiu —Harghita. Mansuscript, Arh. Inst. Geol. București. Institutul Geological României 3 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM 51 ration in 3 areas displaying volcanic phenomena, and (b) on the separation within each of these three areas of two major display stages. In order to obtain more confident conelusions there have been utilized uni- and multi- variate statistical analyses, some among these methods having been for TABLE 2 Relative frequency f% of petrographic types perlaining to the Neozoic volcanism from the Călimani, Gurghiu and Harghita Mountains sludied as for their composition in minor Chemical elements Petrographical type Călimani Gurghiu Harghita I H I+II 1 II I+II I II I+II Dacites Hornblende-andesites Hornblende-pyroxe- 9.8 19.5 11.5 6.0 16.4 50.0 34.5 37.8 47.7 41.1 nes-andesites 4.9 11.5 7.5 12.5 31.0 27.0 28.6 25.0 25.4 Pyroxenes-andesites Basaltic andesites Diorites, microdiorites Gabbros, microgabbros 29.3 36.6 50.0 7.7 11.5 7.7 37.3 25.4 4.5 3.0 25.0 12.5 34.5 32.4 2.7 57.1 14.3 27.3 31.4 2.0 the first time applied to the study of igneous products. The conelusions that were reached are relying not only on the values of either statistical parameter or on the indications of a single multivariate test — elements which separately have only a limited significance — but on the general image which is forming as a result of totalizing and confronting of cha- racteristics suggested by all criteria. The characteristical features of the Chemical composition of each rock association have been established by means of the statistical distri- bution parameters of major components (arithmetric mean x, standard deviation S* and the coefficient of variation V = (^-/kj.lOO). Their estimation was achieved in agreement with the law of normality which Con- trols, as a rule, the distribution of major Chemical components in igneous rocks (R o d i o n o v, 1964). In cases when the number of analytical values n < 10, the standard deviation has been evaluated by the D i x o n’s and M a s s e y’s (1957) functions. The values of parameters are figured in table 3 being supplemented in table 4 by the range X = xmo — x . of contents in SiO2. The study of Chemical relations and implicitly the genetica! ones among the rock associations was made by two methods which utilize the comparison of existent data, the first using their totality, and the second, selection of them. M Institutul Geologic al României IGR/ TABLE 3 Stalislical parameters of major Chemical eleements o 46.7 25.5 co aș oi co c 19.1 CO Ol Ol co 37.2 18 GQ O o T in o 0 c Tj O c 0.25 0.25 0.44 0.80 O IX o CM c o O Ol 1.31 r- m CD r- T-< O 2.07 0 SrN o Ol CD C£ ir cr 8.6 13.5 O T-< 7.1 17.6 21.1 18 GO in cd o Ol CC C o. c c C* C CI T? O CD C 0.22 0 65 0.76 IX o ec Tt O cr O' CO T? Tf CD CO CO CC co 3.09 3 69 3.60 CaO aJ c IC Ol ir IC VI cr O 22.4 13.7 ic 14.5 22.8 21.9 (8 73 Ol CC O c CC CC T T c- c m c T- 1.04 1 42 1.40 IX o o cc ir CC a a o 6.43 7.10 CT O* CD 7.17 6 24 6 38 MgO Tf Ol m a tt co oc Tf 47.3 31.6 CD CO 46.7 40.1 42.2 (8 7} co o 1.26 1.77 1.15 1.02 i> O 1.79 1 13 1.30 IX co cd co o co CC CC O" or Tj O co Ol co c c cr 3.83 2 94 3.08 FeO > co CC i> c cr OC lf 75.0 37.7 O O TT aș cc T? |> CO CC 63.5 !8 73 CM CM v v 5 1.29 0.92 a Y-l 1.18 1 43 1.46 IX uO O- CM CC cr o o O- 1.72 2.44 OC co Ol 3.38 2 11 c cr Ol Fe2 °3 1 V & C c t; a 39.7 31 4 Ol o Cr 0'96 I 52.8 iH 00 c cc cc 1.85 1.48 CM m 2.17 1 37 1.51 |X C~ CC cr c CC CM c T! Cr 4.66 4.72 Ol T? 2.26 2 97 2.86 CO o Ol x | 1 V CC C oc ir O c< 6.3 3 2 c- 3.1 8 0 7.4 «C cc c c cc 1.16 1 54 Tl 0.57 1 47 1.37 O Ol CC m Tt CC cr cr oc Ol o G0 CC 00 cc r-i y- s cc O L- O" tȚ co cr co co oc 03 O t5 i Sri v cc CC r- ir cr cr 7.8 4.2 co m 2.2 E 4 5.1 & m m cr Ol a cc TT 4.67 2.36 Tf c co 1.26 3 2.0 3.03 IX . t* oo m CM v» O ir l> ~ G Călimani I+II f. m.rrKfii I p.u.gu.u X Gurghiu II Gurghiu I + II Harghita I Harghita II Harghita I+II Institutul Geological României 5 EVOLUTION OF MAGMAS DIURING .THE NEOGENE VOLCANISM 53 The B o n d a r e n k o’s method (1968) worked out according to the thesis that silica shows a relatively high inertness in differentiation of magmas suggests that the testing of consanguinity of some rocks should be done in the framework of samples with close contents in silica, TABLE 4 SiO2 range Localization n x min. V mas. Călimani I+H 67 48.69 69.15 Călimani I 50 48.69 69.15 Călimani II 17 49.89 60.80 Gurghiu I+II 37 52.26 64.73 Gurghiu I 6 53.32 64.73 Gurghiu II 31 52.26 61.45 Harghita I+H 51 54.39 67.11 Harghita I 7 55.40 59.28 Harghita II 44 54.39 67.11 which would define a reference moment in the evolution of magmas. In this intersection zone of SiO2 ranges, the differences among the con- tents of other major Chemical components can or cannot be essential. When investigatig the 6 rock associations from the region (Călimani I, Călimani II, Gurghiu I, Gurghiu II, Harghita I, Harghita II), it results that the intersection zone would be A SiO2% = {59.28,55.40} .So as in the case of rock associations from the 3 areas (Călimani I + II, Gurghiu I + II, Harghita I + II) the intersection zone is A SiO2% = = {64.73, 54.37} (Fig. 1). This study was carried out both for associa- tions taken as a whole (fig. 1, tables 5 and 6) and for associations taken as pairs (Plate I, tables 7 and 8). The analysis of differences as to the Chemical composition of sub- collectivities, displaying a common silica range, is achieved for each Chemical element taking into account a pair of rock associations, initially through a graphical procedure. The variation diagram of every element Xj with respect to the SiO2 (Xj — A12O3, Fe2O3...) is represented for a rock association so as it is exemplified in fig. 2. The differences between the distribution of a Chemical element within the two rock associations are evaluated by the difference Zi (see fig. 2 ). The average dispersion variance of the Z variable (when presuming that the actual average of L JA Institutul Geological României kjGR/ 54 DAN RĂDULESCU, ALEXANDRU DIMITRIU 6 a b c Fig. 1. — Relative participation of samples (n %) in common SiO2 range (b), respectively lower (a) and higher (c) for testing consanguinity of rocks pertaining to formations on the whole. Testing of the hypothesis as regards the consanguinity among the volcanics in the three regions (W2) Stages Chemical element Gurghiu I + II Călimani I 4- II > Harghita 14-II A12O3 Fc2Os FeO CaO MgO Na2O K2O 0.57 0.75 0.01 0.18 13.68 3.85 3.69 El 0.03 0.82 2.23 1.16 7.36 0.01 2.37 0.74 Gurghiu I+II A12O3 Fe2O3 FeO CaO MgO Na2O k2 O 0.30 3.39 1.95 1.39 ; 3.96 2.01 5?60~ 18.63 7 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM 55 TABLE 6 Testing of the hypothesis as regards the consaguinity among the volcanics pertaining to various stages of activity (W2) Stages Chemical elements Harghita 11 Gurghiu I Gurghiu II Călimani I Călimani II A12O3 F e2^3 FeO 1.06 0.11 0.03 1.21 1.88 3.30 ! 3.99 1 1 0.60 1.10 0.38 0.09 u.zy 0.03 U.OK 0.10 Harghita I CaO 3.57 10.56 0.48 8.06 0.02 2.29 3.54 9.57 3.59 11.74 |5.79| 114.72 MgO Na,0 K2O 1.20 0.00 1.33 0.08 2.17 0.47 0.93 1.14 ijmțțJ 5.02 4.06 A12O3 Fe2O3 FeO CaO MgO Na?O K2O 0.17 0.01 0.20 2.88 6.23 0.33 1.57 1.07 4.96 0.58 0.00 0.31 0.25 0.24 1.50 6?53 8.19 Harghita II 0.02 14.04 1.32 9.15 0.53 0.42 |30.51 4.44 18.34 0.27 1.17 3.77 3.93 | 4.36 Gurghiu I A12O3 Fe2O3 FeO MgO CaO Na2O K2O 0.07 0.43 0.04 0.35 8.06 2.18 3.49 1.50 0.04 0.15 0.16 0.00 5.16 1.55 2.13 1.13 0.23 2.41 1.40 0.99 3.37 i 15.47 3.56 3.51 A12O3 Fe2O3 FeO 1.03 0.20 0.02 0.15 [6/73; '6.52 Gurghiu II CaO 0.70 9.21 0.14 [21.94 MgO Na2O k2o 1.43 0.21 | 5.18 | 0.61 0.65 | 7.58 1 ai2o3 Fe2O3 FeO i 1.14 [71778 1 8.67 Călimani I CaO j 3,56 |42.86 MgO Na2O K2O 3.69 4.21 J : i _! 9.81 Institutul Geological României 56 ■DAN RĂDULESCU, alexandru dimitriu 8 differences is zero), together with the number of readings define a Wj function (see table 12, where the computations are illustrated by an exam- ple). It is observed that the value of the W2 function is estimated for eaeh Chemical element (Wf) which by totalizing of all Chemical elements TABLE 7 Testing of the hypothesis as regards the consanguinity among the volcanics in the three regions taken as pairs (IV2). Stages Chemical element Gurghiu I + II Călimani I + II AI2O3 0.01 0.22 Fe2O3 0.30 6.24 FeO 0.73 3.98 Harghita CaO 0.45 22.53 0.24 25.25 I + H MgO 0.01 3.40 Na2O 1.31 0.01 K2O 19.72 11.16 A12O3 0.07 Fe2O3 4.13 FeO 2.03 Gurghiu I + II CaO 4.03 15.68 MgO 0.04 Na2O 0.38 I<20 5.00 informs about differences displayed by the whole Chemical composition of rock associations under study. Wj and W2 are controlled by chi-square distribution. The hypothesis as to the eomagmatism relations is admitted as true for < X m.d.f.: o,95 levei of significance. ^hereas the hypothesis implying non- essential differences as regards the distribution of a j element is accepted for Wj < x2df. 0.95 levei of signif. There results that the B o n da- re n k o’s method allows both the test of the eomagmatism (by W2) and the accurate determination of Chemical elements which define the deviations from the magmatic consanguinity (W?). In tables 5—8 the 9 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM 57 TABLE 8 Testing of the hypothesis as regards the consanguinity betiveen the volcanics of activity stages taken as pairs (W2) Stages Chemical element Harghita II Gurghiu I Gurghiu II Călimani I Călimani II Harghita I A12O3 Fe2O3 FeO CaO MgO Na2O K2O 2.76 0.45 3.41 0.40 0.98 0.12 8.72 0.00 2.38 1.43 2.25 5.86 j 1.77 0.01 1.01 9.48 0.00 0.79 0.04 0.12 0.18 0.09 0.46 3.12 iTîr 11.85 1.18 0.00 7.03 0.63 1.03 1^55 17.87 j 1.32 3.64 5/76 0.10 0.04 0.49 13.60 Harghita II A12O3 Fe2O3 FeO CaO MgO Na2O K2O 0.01 0.04 0.88 0.92 2.64 1.02 1.13 0.23 11.77 1 4.00 0.01 0.01 13.01 0.75 15.20 | 5.40 739 129.59 1.30 1 4.16 1 5.77 i 22,01 36.40 | | 4.59 11.88 44.73 5.00 | 0.01 0.01 1.05 3.94 12.35 d Gurghiu I A12O3 Fe2O3 FeO CaO MgO Na2O K2O 1.28 0.03 0.54 0.07 8.99 0.22 0.09 0.09 0.05 1.31 0.67 0.03 0.16 0.51 j 4.46 7.43 0.74 28.19 | 1.18 0.51 | 5.85 j 6.60 | 7.94 0.04 Gurghiu II A12O3 Fe2O3 FeO CaO MgO Na2O K2O 1.72 0.02 1.42 0.23 11.70 0.72 0.98 9.92 14.46 2.34 0.32 45.04|i ■ 7.01 | 0.31 0.58 I 16.71 Călimani I A12O3 Fe2O3 FeO CaO MgO Na2O K2O 0.03 6.84 9.92 6.39 1 39.84| 1.32 7.74 7.60 1 1 1 Institutul Geological României W2 and W j values for cases when the eomagmatism hypothesis is rejected or when one element has a different distribution in the rock associations taken into account, ’were figured in a frame. By contrast with the testing of the similarity of the Chemical com- position only by samples, pertaining to the eommon range of silica, there has been considered as useful the che- cking of equivalence likewise without any restrictions for the silica range ; in this mode there are also included the peripheric portions of the diffe- rentiation domain where the most specific features of phenomena are very frequently materialized. Conse- quently, there have been utili- zed the W i 1 k s’ Miller and K ah n, 1962) and B o d i o no v’s (1968) methods applied in various researches relating to the test of the appurtenance of two or several subcollectivities to a general collec- tivity (subcollectivities of rocks, ores, faunal populations) (I a n o v i c i, Dimitriu, 1968). The W i 1 k s’ V criterion is a logarithmical function of determi- nants of W and S covariance matri- xes, the last matrix being obtained, assuming that the differences among the averages of the Chemical compo- sition of the pairs of considered rock associations are non-essential 7=- L +n2-l- \ 2/1^1 where nu n2 = number of Chemical values of compared rock associations, EVOLUTION OF MAGMAS DIUBING THE NEOGENE VOLCANISM 59 (1) respectively (2); p = number of characteristics (Chemical compo- nents); |W|, 1$ | = determinanta of W and S matrixes. The V has chi-square distribution with p degrees of freedom. There will be accepted as true the hypothesis on the Chemical composi- tion equivalence of rock associations under study for V < x2pdf. 095 The Chemical composition has been represented, as usually by SiO2, A12O3, Fe2O3 + FeO, CaO + MgO and Na2O -j- K2O. As regards the R o d i o n o v’s method the Chemical comparison of two rock associations (noted by Ts and Tk) is carried out by means of the V(T„Tk) whose distribution is likewise chi-square with p degrees of freedom V(T„ Tk) = «jt Ț2 AT __ 1 P nk Zj xti Zj XU -LV x t=l________________________1 =1 ATZAT \ N 1 / N \2~ ^(N-n„)ns (=1 A V-l ) where N = ns + nk TABLE 9 Testing of lhe equivalence of the Chemical composition of volcanics by the V function (according to Wilks) Călimani II Gurghiu I Gurghiu II Harghita I Harghita II Călimani I Călimani II Gurghiu I Gurghiu II Harghita I |21.42 | 2.11 1 22.54 3.37 7.09 9.31 4.70 112.06| 2.93 26.77 49.46 21.43 12.37 Gurghiu I + II Harghita I + II B Călimani I + II Gurghiu I 4- II 3.34 109.31 21.13 NOTE : Chemical compounds introduced into calculations : SiO2, A12O3, Fe2O3 (total), CaO + + MgO., Na2O + K2O. (x* sd.f.: 0.95 = H10) | vj — the hypothesis Ho: = M=2 ‘s Tejected. Institutul Geological României 60 DAN RĂDULESCU, ALEXANDRU DIMITRIU 12 The assumption as to the equivalence of the Chemical composition. of rock associations is admitted as true for V(Ta, Tk) < x2 m.a.f.:0.95. In the calculation of the V (Ts, Tk) function, all the Chemical components both the major and the minor taken individually have been introduced 8. table 10 Testing of the equivalence of the Chemical composition of volcanics— major elements — by the V (Ts,Tk) function according to Rodionov. Călimani II Gurghiu I Gurghiu II Harghita I Harghita II Călimani I [42.95 | | 9.69 | 21.27 19.82 [67.281 Călimani II 58.30 171.621 |60.10 | |78.15 | Gurghiu I 15.14 [25.95 | 17.24 Gurghiu II |45.60 | >80.09 | Harghita I [29.15 | B Călimani I + Gurghiu I IWl [20.09 |22.40 i 166.501 C Călimani I + Gurghiu I+II |68.231 |30.25 | |88.68 [ Gurghiu I + II Harghita I + II Călimani I+II [37.98 | |64.81 Gurghiu I + II |71.88 | Note: Chemical components introduced into calculations: SiO2, A12O3, Fe2O3, FeO, MnO, CaO, MgO, Na2O, TiOa> P2O5, H2O . Z12 d . f.: 0.95 = 21.00 Ho : MSl = M=2 3 The algorithm and a FORTRAN IV program of the method were given by Z a m f i- rescu, Dimitriu, Chirii ă, Dănescu (in prinț). Institutul Geological României 13 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM 61 The difficulties encounterd in the calculation have limited the applying of the W i 1 k s’ method to the investigations on the equivalence TABLE 11 Testing of the equivalence of the Chemical composition of volcanics-trace elements by V(Tf, Tk) function. Călimani II Gurghiu I Gurghiu II Harghita I Harghita II Călimani I 1^1 13.76 |45.03 | (14.301 |133.861 Călimani II |16.311 46.791 [19.941 |150.74 | Gurghiu I [16.21 | 12.54 [51.69 | Gurghiu II [30.32 | |67.25 | Harghita I |48.81 ] Căliman II Gurghiu I + Harghita I |20.44 | I [15.311 |26.321 |67.05| Gurghiu I + II Harghita I + II Călimani I+II [45.50 Gurghiu I+II |169.55 | |76.72 | Note : Chemical components introduced into the calculations : Pb, Cu, Zn, Ni, Co, Cr, V. X2 7d.f.; 0.95 = 14.10 |V (Ts, Tj) is rejected Ho : M=, = M=2 of the Chemical composition, only for major components of the volcanic products (table 9), whereas the R o d i o n o v’s method has been used both for the major components (table 10), for the minor ones (table 11) and for the research according to the type of rocks (table 12). Institutul Geological României DAN RĂDULESCU, ALEXANDRU DIMITRIU 14 TABLE 12 Computation of the Wj function, utilizing the Zt values from Plate I Z. 2. -0.30 0.20 0.55 -0.27 0.00 -0.10 0.30 0.45 0.55 1.00 1.55 0.55 1.30 -1.95 0.00 0.95 0.70 -0.-15 1.70 1.30 1.15 0.20 0.65 -0.10 1.50 0.90 0.25 0.70 0.22.28 Relationships among the volcanic manifestations from the Călimani Gurghiu, Harghita Mts The so far expressed ideas referring to the problem, or those which may be inferred from the carried out research work, are grouped into two categories : In the framework of the first, the acceptanee of a general similarity among the 3 areas (from all the viewpoints) leads to the concept of the simultaneity of volcanic processes; In the framework of the second, the admittance of the existence of some differences among the 3 areas leads to the concept of a succes- sion of phenomena, the advance of the volcanism from N towards S. The analysis of this problem is evidently made more minutely than correspondently of notions ,,province” and volcanic „epoch”; the conclu- sions that will be reached would not contradict, on the one hand, the existence of these geological units — already well proved — and would not aim, on the other hand, to argue again problema already satisfacto- rily substantiated. Institutul Geological României 15 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM 63 The general impression emanating from the analysis of the carried out statistical proeessing is that each of the above 3 areas marks a rather clear-cut individualization. This may be particularly stated în cases when no restrictions as regards the compared SiO2 range are intervening, becaUse even the ampleness of the latter represents the reflection of the evolution degree of magmatic masses, and this degree is itself an element which is to be. compared; from the standpoint of evolution of magmas, the peripheric zones of the SiO2 range would represent the most interes- ting and significant parts. The statistical parameters of the content in major elements (table 3) show clear-cut differences among these 3 areas, in particular, for Fe2O3, CaO and K2O; the significance of differences cannot be attenuated by any of the similitudes of values, which moreover do never concern all the 3 areas (FeO, MgO, Na2O for Harghita and Gurghiu; A12O3 for Harghita and Călimani; SiO2 for Călimani and Gurghiu), and conse- quently are not essential from this point of view. Equally significant there are the variation ranges of the parameter values, so as it may be for instance, stated for SiO2, from the table 4; the above 3 areas are very clearly individualized. The results of the multivariate analysis also plead in that sense. The W2 criterion (table 7), as well as the V(Ts,Tk) criterion (table 10) point out essential differences among the 3 areas for the major Chemical elements. Differences among the 3 areas are not obvious only with respect to major components, but, to the same extent, the minor ones ; the V(Ts,Tk) criterion points out for this time too, essential differences (table 11). Another way the differences among the 3 areas are displaying, consists probably, in the modification of the variability degree of diffe- rent features. The statistical values from tables 3 and 4 suggest a tendency for „stabilization” of this variability from N toward S within the Călimani-Gurghiu-Harghita succession. However, such an observation is not supported by all the data, and within the same parameters contra- dictory observations may be also forwarded (table 3). A more minute analysis of various values points out that within these differences, the 3 areas do not display an identica! behaviour. All data indicate that the Harghita area occupies a special position as the characteristics of its products may be opposed both to those from the Călimani area and to those from the Gurghiu area. In some cases the differences between the Harghita and Gurghiu areas and between Harghita and Călimani areas are readily discernible, by contrast 'A Institutul Geologic al României IGR/ •64 DAN RADULESCU, ALEXANDRU DEMITRTU 16 with resemblance between the Călimani and Gurghiu areas (W i 1 k s’ criterion, table 9). In other cases the situation is not so easily discernible. Thus, most surprizingly with respect to the previous affirmation, the W2 criterion indicates clear resemblance between the Harghita and Călimani areas and between Harghita and Gurghiu areas (table 5). Nevertheless, as (a) the differences among these 3 areas are precisely indicated by other parameters (tables 3, 4, 7, 10, 11), and as (b) they suggest a non-simulta- neity of volcanic manifestations it may be presumed that in the Harghita area supplementary elements had intervened, which have secondarily created a similitude that is revealed only by some parameters. This supplementary intervention represents itself a characteristic feature for the Harghita area. The individualization of the Harghita area by means of a subse- quent intervention of characteristic elements is also indicated by the fact that the general SiO2 range is established hardly during the second stage of the evolution, whereas in the Călimani and Gurghiu areas this range is defined still from the first stage (table 4). The same explana- tion might be given also for the attenuation of the tendency to stabih- zation of the characters within the Călimani —Gurghiu—Harghita succes- sion (previously mentioned) which in the Harghita area, was displaying also during the second stage of volcanism. In conclusion it would seem, that after having statistically examined the distribution of the major and minor Chemical components of volcanic rocks, we may state that, in the framework of the general similarities defining the petrological province, there exist numerous minute differences among the volcanic products of the Călimani, Gurghiu, Harghita areas which allow to delimit each of them as regards the Chemical evolution of magmas. Such a conclusion suggests some discre- pancy in time between the volcanic manifestations of the above 3 areas. On the background of differences, which may be considered as having been generated by normal magmatic differentiation processes a somewhat especial position is occupied by the Harghita area where it would seem that a disturbance had occured in the late moments of the magmatic evolution. Relationships between the evolution stages oî volcanism within the 3 areas Almost all parameters indicate the similarity of the first stages of volcanism from the 3 areas. The W i 1 k s’, R o d i o n o v’s and W2 Institutul Geological României 17 EVOLUinON OF MAGMAS DIURING THE NEOGENE VOLCANISM 65 criteria (tables 8, 9, 10) for major components like the V(TS, Tk) function (table 11) for minor components do completely agree. The differences among the 3 areas, prove to have been generated during the second stage of the volcanic activity. Most criteria point to the lack of similitude between these stages both as for the major compo- nents (tables 8, 9) and as to the minor ones (table 11). The examination of relationships between the two stages has evidenced firstly the peculiar position of the Harghita area. Here a clear-cut individualization is displayed by the the second stage, which shows the features of a disturbance as compared to the inter-stage rela- tions in the Călimani and Gurghiu areas. A first observation, the one relating to the definitization of the limits of the SiO2 range, has been already made (table 4). The peculiar situation of the second stage in Harghita Mts is indicated also by the increase of the x value for most major components from the first to the second stage in the Harghita area by contrast with its decrease in the Călimani and the Gurghiu areas (table 3). The spreading of S5 displays likewise a peculiar behaviour in the Harghita area as compared to the othei’ two areas (table 8). For some criteria the particular position of the second stage of the Harghita area is reflected either in a constant diffe- rence between it and the other stages of the 3 areas, by contrast with the variable character of relationships between the latter, or by the fact that a stage appears with affinities with respect to all anothers, excep- ting the second stage of the Harghita area, with which it marks an essential difference (table 9). It is noteworthy that for some criteria the values indicate a simi- larity between the two stages of the Harghita area, but it is only appa- rent. Thus, for instance, in the case of the W2 criterion (tables 6 and 8) the differences for SiO2 do not appear owing to the nature of the crite- rion, but they exist for A12O3; despite the similarity indicated by this criterion for the global Chemical composition, one must consider as more significant the differences for these two essential components. The so far presented data are not to be considered as indications that the relationships between the stages of the Călimani and Gurghiu areas, being different from those of the Harghita area, are still very much alike between them. In the various cases the relations are not completely homogeneous, but the relationships among the stages, their „filiation” in each of the two areas is out of question. The relations among the stages of the Gurghiu area, show more constancy than those of the Căli- 5-C. 630 Institutul Geologic al României 66 DAN RĂDULESCU’, ALEXANDRU DIMITRIU 18 mani area. The first suggestions in this respect are given by the average values for A12O3, Fe2O3 etc. (table 3). However, as very significant may be considered the values of the W2 (table 8), Wi 1 k s’ (table 9) R o di o- n o v’s (table 10) criteria which are pointing out an obvious relationship between the two activity stages from the Gurghiu Mts. The examining of relations among the stages of volcanic activity has outlined in addition two general ideas. The first is concerning the occurrence of differences among the 3 areas only during the second volcanic stage, starting from a homogenous background in the first stage. The second is concerning the causes of these differences; for the Harghita area the interference of an externai perturbant factor is specified, whereas the existence of „filiation” in the other two areas allows to explain the global differences by the non-simultaneity of processes. Conclusions The image of the unfolding of volcanic processes over the area of the Călimani, Gurghiu and Harghita Mts, resulting from the study effected, is essentialy detailed and more precise as compared to the previous ones. The existence of some distinctive features for the 3 areas was already pointed out (Rădulescu, 1963), still the analyses did not tackle the detecting of the mechanism and the causes of these differences. Today we may forward the following assumption which, developed on the basis of Chemical data, is consistent with all the already known geological elements. The magmatic activity over the whole territory is characterized at its beginning by the Chemical homogeneity of its products. Thus, it is suggested that the magma masses had not undergone longlasting evolutions within their various subcrustal magma chambers, which might have conferred them independant features. We may rightly consider that the ascent of magmas toward these high levels of the crust did not precede for a long time the beginning of the volcanic activity. The development of the volcanic activity was stimulating — by discharges of thermic and mechanic energy, by extraction of considerable bulks of substance — the differentiation processes; having certainly began still some time before the subaerial activity they marked an accentuation in these moments determining not only the variation of products from this first activity stage but especially creating premises for the variability of the following stage. Institutul Geological României 19 EVOLUTION OF MAGMAS DIURING THE NEOGENE VOLCANISM If we take the assumption that the inițial magmatic material dis- played common characters in all the 3 areas, then it may be supposed that the timeinterval of the differentiation was the chief factor respon- sible for the variability of the petrographical characters during the second stage of activity. Thus the hypothesis is suggested that volcanic manifestations did not simultaneously occur in the 3 areas; it is true that this hypothesis does not present the single possibility to explain the situation, but it corresponds to numerous suggestions given in this sense likewise by the geological characteristics.From the point of view under discussion, it is impossible to make an affirmation as to the begin- ning of the supracrustal activity. Elements of Chemical nature — corres- ponding to elements of geologic nature — compel us to accept the non- simultaneity of the limit between the two stages and of the closing moments of the activity in all the 3 areas (Rădulescu, in prinț). Consequently there would have been periods of coexistence of various stages in these 3 areas, assumption supported by the lack of funda- mental opposition from the Chemical point of view between the upper stage and the lower one from adjacent areas in the Călimani —Gurghiu — Harghita succession. However, we are not inclined to afford a too large extension those periods of coexistence. The unfolding of the differentiation processes has led to essential differences among the products of the second stage in all the 3 areas. In the Călimani and Gurghiu Mts the evolutive character of the transition from the first stage to the seconl one is obvious. Nevertheless, it is most probable that in the Harghita Mts the peculiarities proceeding from the differentiation have been superposed by an externai strong pertur- bation factor. The wide pronounced extension of the SiO2 range duiing the second stage, and the constant differences indicated by the statistica of the A12O3 contents from these two stages make us to presume an interference of a silico-aluminous material — may be an assimilation of sedimentary rocks — to constitute the cause of perturbance. This hypothesis corresponds with the existing differences as regards the nature of the basement between the Southern outermost part of the eruptive chain, on the one hand, and the median and northern sectors, on the other hand (Rădulescu, this volume). Institutul Geological României 68 DAN RĂDULESCU, ALEXANDRU DIMITRIU 20 REFEBENCES B o n d a r e n k o V. N. (1968). Problema gheneticeskovo rodstva magmaticeskih tel i eio veroiatnostnaia pastanovka. Sb. „Matematiceskie metod! v gheologhii”. Izd. Nauka. Moskva. Dixon W. J., Massey F. J. (1957). Introduction to statistical analysis. Mc. Graw-Hill. New York. Ia no viei V., Măldărescu I., David B., Bratosin Ir in a (1968). Quelques particulariUs concernant les teneurs en certains elements-traces dans les volcanites des Carpates Orientales. Rev. roum. geol. giophys. giogr. Sir. Giol., 12, 1. Bucarest. I a n o v i c i V., Dimitriu AI. (1968). Considerații asupra genezei zăcămintelor de mangan din munții Sebeșului. Stud. cerc. geol. geof. geogr. Ser. Geol., 13, 1. București. M i 11 e r R. L., K a h n J. S. (1962). Statistical analysis in geological Sciences. J. Willey a. Sons. New York. Rădulescu D. (1961). Contribuții la cunoașterea caracterelor chimice ale rocilor vulcanice tinere de la interiorul arcului carpatic. Stud. cerc, geol., 6. 2. București. Rădulescu D. (1963). Studiul petrochimic comparativ al rocilor vulcanice neogene din R.P.R. Al V-lea Congr. A soc. geol. Carpato-balc. II, seci. 1 Mineral.-Petr. București. Rădulescu D. (in prinț). Considerații asupra cronologiei proceselor vulcanice neogene din munții Călimani—Gurghiu și Flarghita. D. S. Inst. geol. LIX/4. București. Rădulescu D. (1973). Position of the Călimani —Gurghiu —Harghita Area within the Neozoic Volcanic Zone of the Alpine Regions (this volume). Rădulescu D,. Stiopol V. (1964). Contribuții la cunoașterea distribuției elementelor minore în andezitele din munții Gurghiu și Harghita. An. Com. Geol., 34. București. Rădulescu D., B o r c o ș M, (1968). Aperfu general sur l'evolution du volcanisme neogene en Roumanie. Ann. Com. Geol., 36. București. R o d i a n o v D. A. (1964). Funcții raspredelenia soderjanii elementov i mineralov v izver- jennîh gornih parodah. Nauka . Moskva. R o d i o n o v D. A. (1968). Statisticeskie metodî razgranicenia gheologhiceskih obiektov po kompleksu priznakov. Nedra. Moskva. Zamfirescu R., Dimitriu Al., Chirilă A., Dănescu R. (in prinț). Un program pentru compararea eșantioanelor m-dimensionale (programul GEO2). Rev. de statistică, București. Institutul Geological României DAN RĂDULESCU, AL. DIMITRIU-Considerotions on the Evolution of Magme; during the Neogene Volcanism in the Câlimani, Gurghiu and Harghito Mts. RELATIVE PARTICIPATION OF.SAMPLES (n%) WITHIN THE COMMON (b), RESPECTIVELE LOWER (a) AND HIGHER (c)SiO2 RANGE ON PURPOSE TO TEST THE CONSANGUINITY OF ROCK ASSOCIATION PAIRS CĂLIMANI I GURGHIU I HARGHITA I CĂLIMANI II GURGHIU II HARGHITA II CÂLIMANI I GURGHIU I CĂLIMANI 11/ CĂLIMANI II HARGHITA I HARGHITA I GURGHIU II HARGHITA II CĂLIMANI I GURGHIU I GURGHIU HARGHITA HARGHITA HARGHITA II CĂLIMANI II CĂLIMANI l,ll_[ HARGHITA l.ll ANUARUL INSTITUTULUI GEOLOGIC VOL. XLI Imprim- Atei. Inst. Institutul Geologic al României CONSIDERATIONS ON THE ORIGIN OF MAGMAS OF THE NEOZOIC SUBSEQUENT VOLCANISM IN THE EAST CARPATHIANS BY DAN P. RĂDULESCU 1 A problem of major interest for the geology of the East Carpat- hians — the origin of magmas, whose subaerial or subcrustal consoli- dation gave rise to the volcanic zone — was but rarely tackled. H. Stille (1953) is practically the single scientist who has discussed this problem with more details, and has endeavoured to prove the exclu- sively lithogenous origin of Neozoic magmas from the Carpathians. His conception was later adopted by most investigators of the above region, this standpoint corresponding with the general tendency displayed by the evolution of ideas on the origin of magmas in the orogenic region (1940—1960). Concomitantly with the accumulation in these last years of observational data relating to the Romanian Carpathians, the accep- tance of this hypothesis has met with ever more difficulties; without denying the local formation of magmas by melting of pre-existent rocks, we have the impression that nowadays the question ,,how were generated magmas in the course of theNeozoic within the Romanian Carpathians?” is to be otherwise answered. Almost unanimous in considering the melting as the single process for the formation of andesitic magmas, the researchers of the last decades had nevertheless essentially different opinions even as for the main features of this phenomenon; the diffe- rences of opinions have always reflected the chief difficulties encountered in the working out and acceptance of this hypothesis even by its most devoted supporters. 1 Facultatea de Geologie—Geografie, Bd. Bălcescu, 1, București. Institutul Geologic al României 70 dan rădulescu 2 These last years some doubts that many researchers have had as regards the lithogenous nature of andesitic magmatism were confirmed. It is sufficient to mention a situation as that from the northern part of the central America, where the impossibility to accept such a hypot- hesis has been recently proved (W e y 1, 1966, 1967). The volcanism which had developed here during the Neogene — although showing petrographical and Chemical features of a subsequent magmatism — does not correspond with any close in time orogenesis to which it could be referable. Its development over an oceanic basement, the sialic crust lacking, and the absence of any indications with respect to the sinking of more recent sedimenta, are excluding the possibility of a lithogenous nature for magmas. Very strong arguments for the interpretation of the genesis of andesites have been then obtained owing to the investigation of the distribution of trace elements both in andesites and in other volcanic rocks (Doe et al., 1968 ; T a y 1 o r, 1968). The massive pre- sence of andesites during the geosynclinal magmatism, displaying charac- ters perfectly corresponding to those of rocks from the subsequent volca- nism, is also particularly significant (Dickinson, 1964); in such cases too the lithogenous formation of andesitic magmas seems to be out of question. Later on numerous andesite occurrences, without any connection with the sialic crust, have been identified outside the orogenic regions (Kuno, 1968). Observations of this nature are as yet relatively scarce but it is obvious that the problem relating to the origin of andesitic magmas is to be reconsidered. Today attemps are made to specify criteria which would permit the separation of lithogenous andesites — whose existence is not out of question — from the hypogene ones. The study of the distribution of trace components, and that of the isotopical composition of some elements leads not only to significant results but, occasionally to contra- dictory ones. It would seem that, as yet, solely the geological criteria may be considered as having a general validity, whereas the other ones may by useful according to the case under study. However, it is doubtless that the most important element in discus- sing this problem would be today the plate tectonics concept. Although the mechanism of the unfolding of processes and their details are far to be as yet known, nevertheless it would seem that no impediment of geological and geophysical nature should exist as to derive volcanic pheno- mena in orogenic areas from the subduction of oceanic crust. The imme- diate implication resulting from the acceptance of this hypothesis consists jMp Institutul Geological României ICR/ 3 ORIGIN OF NEOZOIC MAGMAS IN THE EAST CARPATHIANS 71 essentially in admitting a deep-seated source for andesitic magmas with eventual contaminations during the ascent and stops at intermediary levels of the crust. The reticences that the researchers of the Neozoic volcanic regions from Romania have had as regards the lithogenous origin of magmas, became more accentuated these last years concomitantly with the accumu- lation of obsei vational data; further on we will present some principal aspects of the problem where the ineompatibility with the hypothesis relating to the lithogenous nature of the andesites is obvious. Partially they do correspond to a rather rich observational material, and partially they represent only comments of a quite general character. Owing to the nature of this problem a part of considerations hereafter do not only refer to the Călimani —Gurghiu—Harghita area, but may be also applied to the other regions with Neozoic volcanism from the East Carpathians. Association oî andesites wilh basalts Although the products of the subsequent igneous activity cover in Romania the whole range of petrographical types charaeteristic of calc-alkaline magmas, its specific feature is a clear-cut predominance of andesites over rhyolites, dacites and basalts. This predominance is mostly conspicuous within the Călimani— Gurghiu—Harghita area where there are practically present exclusively andesitic rocks and their extremely basic forms. It is to be emphasized that, here the basalts are perfectly typical from all points of view; if we also take into account the fact that this area is partially located along the trajectory of a deep fracture — on which have raised, at least, in some moments, basic magmas, which have generated basalts (Rădulescu, 1969) — then the presence of the hypogene magma is out of question. To what extent, however, the andesites might be its products? The chief observation to be made is that a large part of andesites display pronounced basic features; the silica content may be of 51 per cent without any essential petrographical changes, whereas occasionally the existence of olivine does concretize also from the mineralogica! stand- point, their basic character. Such rocks are abundant in more recent activity phases, however, they never lack in the oldest ones. They are described in the Romanian relevant literature under the name of basalt - like or basaltic andesites. Both the basalts proper, and particularly the basic forms of andesites are present in the whole Călimani —Gurghiu — Institutul Geologic al României 72 DAN RĂDULESCU 4 Harghita area. The Chemical composition and the areal distribution of basalts and basalt-like andesites justify the presumption of their gene- tica! relationship. On the other hand, however, the basalt-like andesites cannot be separated from the andesites s.s. which build up the most important mass of volcanic products; the Chemical, petrographical, geological features display their close relationship. The petrochemical analysis of the whole petrological province has proved that one of its essential features is that the basic and intermediary domains are closely related, whereas the acid domain appears as separated from the intermediary one (Rădulescu, 1961, 1963). Thus the products with an inter- mediary and basic composition prove to have a genetically common nature. The coexistence of andesites and basalts within the same petrologie province is occasionally used as an argument for the accep- tance of their common genesis (K u n o, 1968); the situation in this region is more favourable since their relationship is chemically and petrologically proved. Chemical composition of volcanics and their evolution The numerous results, obtained in the research on the Chemical composition of rocks, are likewise significant. Although the lack of some precise criteria in order to separate the hypogene material from the litho- genous one prevent from obtaining certain conelusions, some comments can be forwarded relying on the very abundant Chemical material. In the case when magmas were formed by melting of preexisting rocks it might be expected that the ,,non-magmatic” nature of the inițial material has been to some extent reflected in final products, even if its complexity and the subsequent evolution of the melting would have determined the gain of new characters. Really, both the distribution of major elements and that of trace elements tally quite satisfactorily with the fundamental features of the hypogene magmas; although as yet insufficient in number, nevertheless particularly the results of researches on the distribution of trace elements lead to such conelusions (Rădulescu, S t i o p o 1, 1964 , Ian o vi ci et al., 1968); for instance, the high Ni-content in all the rocks is to be stressed (P e 11 z, Braț o sin, 1971). The petrochemical characters of the Neozoic magmatic province in the innerside of the Carpathian Arc over the territory of Romauia, have been examined in details (Rădulescu, 1963; Rădulescu, A Institutul Geologic al României 16 R/ 5 ORIGIN OF NEOZOIC MAGMAS IN THE EAST OA1RPATHIANS 73. B o r c o ș, 1968), and some data of this nature may be used in discussing the genesis of magmas. The evolution in time of the composition of magmas has broadly developed from acidic to basic, and we presume that this fundamental character of the magmatic province is inconsistent with the hypothesis on the formation of magmas by fusion. If magmas would be lithogenous, they would have undergone, after their genesis, differentiation processes there resulting more and more acid products. Accepting as indiscutable the fact that the basalts and — according to the above expounded reaso- ning — the basalt-like andesites would represent the hypogene magma which closed the subsequent igneous activity, it would be necessaryr that at least until the occurrence of basalt-like andesites, this evolution trend of the Chemical composition of magma should be observed. Really the Neozoic magmatism starts with rhyolites and evoluates through dacites up to normal andesites, even before the occurrence of basalt-like andesites. On the other hand, there is no ground to presume that at the beginning of the subsequent volcanism, magmas were exclusively of lithogenous nature, and later on the possibility of a hypogene supply to have occured. The hypogene character of basalts being doubtless, it is more normal that this mechanism of genesis to have been accepted for the whole subsequent period. Giving up the hypothesis on the lithogenous character of magmas, the Chemical composition may be explained by the succession of supplies of magma from depth in varied contamination and differentiation stages. The differences which were observed among various parts of the Căli- mani—Gurghiu—Harghita area (Rădulescu, Dimitriu, this volume) are perfectly consistent with this way to envisage things. Presence of meialliferous ore deposits In the Carpathians, important ore deposits of native gold and silver, lead and zinc sulphides (as well as subordinately some other ele- ments) are associated with the subsequent magmatism ; they display homogeneous features over the whole area. The possibility to separate the metallic elements from the pie-exis- ting rocks submitted to a melting process, and their concentration up to the form which would permit the genesis of ore bodies is certainly possible. In our opinion it would, however, seem that in the case under discussion,. most of the features of the occurrence, do rather correspond to a hypo- gene source of material. Particularly the constancy as to the occurrence Institutul Geologic al României 74 DAN RADUD0SCU 6 of ore deposits, and the constancy of parageneses and of main Chemical elements are facts that could be but hardly explained in the case when the formation of magmas would has taken place by the meltings of a preexistent material; the latter would have doubtlessly presented essen- tial variations in its composition within regions as extended as those affected by the Neozoic magmatism. On the contrary, the uniformity of the Chemical features of hypogene magmas — even if they were sepa- rated in numerous chambers showing a different evolution — provides a much more fitting explanation for the existent situation. On the other hand, even in light of the rather uncertain data at our disposal on the unfolding of intratelluric magmatic phenomenathe factor „time” may be discussed. It would seem difficnit to prove that the time interval comprised between the presumed fusion of pre-existing rocks and the appearance of ore deposits, has been sufficiently long for the development of the differentiation and concentration processes which would lead to ore forming fluids. Petrographical charaeteristics of zones of presumed melting The Neozoic subsequent magmatism has shown a particularly homogeneous character along the Carpathians Mts, both over the Romanian territory and outside it; the petrochemical and petrographical variation is achieved within normal limits without affecting this homogeneity. Such an affirmation may be forwarded, as previously stated with respect to the associated ore deposits too. On these grounds it is to be presumed that the material from which the rocks have formed had shown the same chief features in its whole mass. Such a presumption is perfectly consistent with the hypothesis of a hypogene magma; nevertheless it would be necessary to prove, in a particular way, that the lithogenous processes would have allowed to obtain magmas with so homogenous features in such an extended region. If we should examine, no matter how summarily, the informaticii at our disposal about the deep zones, which would had been submitted to melting along the Carpathians — Romania, USSR, Czechoslovakia, Hungary — the existence of essential petrographical differences could be stated : although, the melting processes are to be envisioned as affecting large masses of rocks and therefore, with the possibility of totalizing various Chemical features, it would be normal that in resulted magmas, some of the original differences should reappear, even under attenuate forms. JA Institutul Geologic al României igr/ 7 ORIGIN OF NEOZOIC MAGMAS IN THE EAST OAlR'PATHIANS 75 ★ The ideas commented here, represent in our conception elements of inconsistency between the hypothesis on the lithogeneous nature of magmas and the actual situation in the Romanian Carpathians; today no decisive argument in our opinion could be forwarded to support this point of view. It is much more probable that the origin of large masses of andesitic material is to be looked for in the modifications undergone by the hypogene magma as a result of the differentiation processes, and eventually the contamination ones. Recently an attempt aiming at the inteipretation of the structure of the Carpathian area in the light of the plate tectonics concept (R ă d u- 1 es cu and S ă n d u 1 e s c u, 1973) was made. The fact that the tota- lity of geological features may be satisfactorily framed in this hypothesis, as well as the fact that the decisive part of the underthrust processes in the building up of the structure of the Carpathians had been long ago recognized, have logically led to accept the subduction of an oceanic- type crust from E towards W beneath the present structure of the Carpat- hians ; it would have constitute the source of basic material, which in the course of the ascent, due to the contamination and differentiation processes, would have become magmas released in the framework of subsequent volcanism from the innerside of the Carpathians (S t i 11 e, 1953, presumed the sinking of sialic masses and the generation of magmas by their melting). Although it is difficult to estimate to what extent the magmas were contamined we presume that from the quantitative viewpoint the sialic material has always remained subordinated, and even if it has occasionally determined readily recognizable modifications did not succeed to affect the fundamental features of magma and its homogeneity. The existing petrographical variation — andesites of diverse types, dacites, rhyolites — is due first to differentiation phenomena, and to a less extent, to qualitative and quantitative differences as for the assimilated material. REFERENCES D ickinson W. R. (1962) Petrogenetic Significance of Geosinclinal Andesitic Volcanism along the Pacific Margin of North America. Bull. Geol. Soc. Amer., 73, 10. Washington. D o e B. R., L i p m a n P. W., H e d g e C. E. (1968) Radiogenic Tracers and the Source of Continental Andesites : A Beginning at the San Juan Volcanic Field, Colorado. Ini. Upper Mantie Project. Sc. Rep. 16. Prcceed. Andesite Conf., Eugen, Oregon, U.S.A. Institutul Geological României 76 DAN RĂDULESCU 8 1 a n o v ici V., M ă 1 d ă r ă s c u I., David B., Bratosin Irina (1968) Quelques particularites concernant les teneurs en certains ăKments-traces dans les volcanites des Carpates Orientales. Rev. Rotim. GM. Giophys. Giogr. Ser. Geol.. 12, 1. București. Kuno H. (1968) Andesite in Time and Space. Int. Vpper Mantie Project. Sc. Rep. 16. Pro- ceed. Andesite Conf., Eugen Oregon U.S.A. Peltz S., Bratosin Irina (1971) Trace Elements in Pliocene and Quaternary Basaltic Rocks of Romania. Rev. Roum. Geol. Giophys. Geogr. Ser. Geol., 15, 1. București. Rădulescu D. (1961) Contribuții la cunoașterea caracterelor chimice ale rocilor vulcanice tinere dc la interiorul arcului carpatic. Acad. R.P.R., Slud. cerc, geol., 6, 2. București. Rădulescu D. (1963) Studiul petrochimic comparativ al rocilor vulcanice neogene din R.P.R. Al V-lea Congr. Asoc. geol. Carpato-balc. II, secf. 1, Mineral,-pelr. București. Rădulescu D. (1969) Uber die Anwesenheit einer Tiefenbruchzone enllang dem 25°30' ostlichen Meridian, zwischen 42° und 47° nordlicher Breite. Geol. Rundschau, 59, 1. Stuttgart. Rădulescu D., Stiopol Victoria (1964) Contribuții la cunoașterea distribuției elementelor minore în andezitele clin munții Gurghiu și Harghita. Am Com. Geol., 34. București. Rădulescu D., Borcoș M. (1968) Aperțu general sur l’evolution du volcanisme neogene en Roumanie. An. Com. Geol., 36. București. Rădulescu D., Dimitriu Al. (1973) Considerations on the Evolution of Magmas during the Neogene Volcanism in the Călimani, Gurghiu and Harghita Mountains (this volume). Rădulescu D. P., S ă n d u 1 e s c u M. (1973) Plate tectonics concept and the geological structure of the Carpathians. Tectonophysics, 16. Amsterdam. St iile H. (1953) Der geotektonische Werdcgang der Karpathen. Geol. Reiheft. VIII. Hannover. T a y 1 o r S. R. (1968) Trace Element Chemistry of Andesites and Associated Calc-Alkaline Rocks. Int. Vpper Mantie Project. Sc. Rep. 16. Proceed. Andesite Conf., Eugen, Oregon V.S.A. AV e i 1 R. (1966) Tektonik, Magmatismus und Krustenbau in Mittelamerika und Westindien. Geotekt. Forsch. H. 23. Stuttgart. AV e i 1 R. (1967) Krustenbau und sialischer Magmatismus. Geol. Rundschau, 56, 2. Stuttgart Institutul Geological României TENTATIVE PALEOGEOGRAPHICAL RECONSTITUTION OF THE CĂLIMANI —GURGHIU—HARGHITA AREA DURING THE NEOZOIC VOLCANIC ACTIVITY BY DAN P. RĂDULESCU1 Both the general lines and some details of the paleogeogiaphical evolution of the Călimani —Gurghiu—Harghita Chain have been already cleared up (Rădulescu, 1968; Rădulescu, Peltz, 1970). The main still existing uncertain points are chiefly due to the impossibility to state the precise moment of the beginning of the volcanic activity. All attempts related to the dating of the volcanic activity have so far represented mainly geological interpretations of a general nature, and to a less extent, they rely on objective Information specific to this region. The examining of the stratigraphical position of the emerite horizons from adjacent regions could not lead to conclusive results; if we exclude the Transylvania Depression — in whose deposits the pyroclastic material supplied by the eastern source (Călimani, Gurghiu, Harghita Mts) cannot be separated from that of the northern (Oaș —Gutîi Mts) and western sources (Apuseni Mountains) — outside the Carpathian Arc, the situation presents contradictory aspects. Within the Moldavian Platform deposits, the emerite horizons are lacking on ante-Meotian deposits (excepting the horizon identified at Hudești whose significance cannot be, however, considered as clear-cut) fact that would correspond with the information recently provided by Anton Popesc u 2 on the beginning of the volcanic activity in the Călimani —Gurghiu—Harghita area. However, cinerites are present and rather frequent in the deposits of the inner foredeep, both in the Eastern Carpathians and in the Getic Depression 1 Facultatea de Geologie—Geografie, Bd. Bălcescu, 1, București. 2 A. Popesc u (1966) Studiul mineralelor grele din depozitele pannoniene situate între valea Mureșului și valea Gurghiului Manuscript Arh. Inst. Geol. Institutul Geological României 78 dan rădulescu 2 in deposits of Sarmatian, Tortonian, Helvetian and even Aquitanian age; which is their source? Which is the significance of their distribution only in the bend region of the Oarpathian Arc and in the Getic Depres- sion ? Their concentration in the bend area of the Carpathians — if we would exclude from our discussion the Getic Depression, where the intervention of materials from other sources is quite probable — would seem to indicate the absence of a relationship with volcanic phenomena whose products are nowadays conspicuous in the Călimani —Gurghiu- Harghita Chain; their presence here in deposits of such ages, and even older, has already led to some speculations relating to the possibility of the existence of eruption centres in this region (F i 1 i p e s c u, 1944). However, on the other hand, the existence of cinerites within deposits Meotian in age from the same region is to be related to the activity of the Călimani —Gurghiu—Harghita Chain; hence must we reach the conclusion that the older cinerites too proceeded from the same source or, on the contrary, must we consider that in the course of time other sources as yet not evidenced had existed ? The only objective data which might substantiate a conclusion are as follows : (a) within the Pannonian s.s. deposits in the neighbourhood of the Călimani —Gurghiu—Harghita Chain the volcanic constituents are completely absent beneath the E Zone (A. Popescu, op. cit.), and (b) the absolute ages of about 7 m.y. for rocks pertaining to the basal part of the upper compartment (R ă d u 1 e s c u, in prinț). In the light of these observations no connection, not even with the cinerites of the Lower Pannonian age from the Transylvania Depression (Bazna cinerites) nor with those from the outer side of the Oarpathian Arc, in the Getic Depression, could have been presumed. Really, how could be explained the fact that at a large distance ash tuff deposits displaying essential thickness have accumulated, whereas in the close vicinity of apparata, volcanogenous components either pyro- or epiclastic are completely lacking ? Since the object of our today researches is the observabk volcanic material, conspicuous in the Călimani— Gurghiu—Harghita area, we will hence rely only on it for our conclusions; any connection with ante-Pannonian pyroclastics from neighbouring regions seems to be so far but mere speculations. Nevertheless, in this discussion the interest for dating, the begin- ning of the volcanic activity is not only chronological, but particularly paleogeographical. The latest reconstitutions for the whole territory of Eomania (Lithofacial map 1 :2,000,000—1969) have pointed out that in ■ ' A Institutul Geological României VicrV 3 (PALEOGEOGRARHICAL REICONSTITUTION DURING THE NEOZOIC VOLCANISM 79 the course of the Neogene there had existed a single short time interval when the waters of the Pannonian Lake have covered the region of the Călimani —Gurghiu—Harghita Chain, as far as the axial zone : Pannonian s.s.; during the rest of the time it was a part of the land which separated the Pannonian Basin from the Dacic —Getic one. Hence, if we admit the beginning of the volcanism as having taken place in the inițial or middle part of the Neogene time, we should be bound to imagine it as starting with a subaerial activity, whereas if we admit the beginning of processes as having occurred in the course of the Pannonian, they might initially have had a subaquatic character; the latter is the view- point we expounded in previous papers (R ă d u 1 e s c u, 1968), and which in our opinion seems to be so far justified. The Pannonian 3 is the time when the waters of the Pannonian Lake had extended eastwards covering — with exception of a small area in the northern part — the whole territory nowadays occupied by volcanic products. Relying on the argument yielded by A. Popesc u as to the occurrence of volcanic elements in the Pannonian deposits, we may connect the beginning of the volcanic activity with this moment. Other information as yet not generally valid may be also referred to in this sense; it is for instance the case of volcanic rocks with features of subaquatic consolidation, pointed ont in the northern part of the Călimani Mts 4. The starting of the activity and the building up of the first volcanic structures were sudden and rapid (plate, moment 2). A row of volcanic islands has appeared nearby the eastern bordei’ of the lake; probably more numerous at the beginning, they have finally formed some more important land masses separated by the arms of the lake (plate, moment 3a). If the localization of the piercement points was approximately preserved during the two phases of the volcanic activity, it may be expected that at least within the regions of the present Mureș, Gurghiu, Tîrnava Mare valleys a connection between the peripheral part (eastern) of the lake and its central part would have been achieved (fig. 1, moment 3a) 3 Owing to lacks in our tknowledge of the absolute chronology of volcanic phenomena, special attention inust be paid to the succession of events and not to their exact dating. 1 C o s ni a S t a n c i u, O. Gheruci (1958) Raport geologic asupra lucrărilor de cartări și prospecțiuni in Mții. Călimani —Birgău (Dornișoara— Fîntînele) Manuscript Arh. Inst. Geol. .80 DAN RĂDULESCU 4 Institutul Geological României 5 PALEOGEOGRAPHICAL REOONSTITUTION DURING THE NEOZOIC VOLCANISM 81 Institutul Geological României 82 DAN RĂDULESCU 6 The phenomena thus imagined, one may presume the start of the volcanic activity had taken place in the middle or in the basal part of the Pannonian s.s., with a weak implication in the sedimentary deposits of the adjacent regions, probably due to the subaquatic character of processes. Hardly, at the limit between the C'/D and E zones, the emer- sion of volcanic apparata and the occurrence of a strongly explosive character have determined the appearance of volcanic component» in the sedimentary deposits. The character of the subaerial volcanic activity has been at its beginning extremely explosive. The abundance of cinerites within Meotian deposits from the onterside of the Carpathian Arc constitues a condu- și ve proof ; both the possibility of interference for other sources of pyro- dastic material and the uncertain points existing as to the knowledge of the stratigraphy of Pannonian deposits from the Transyhania Depres- sion do not allow us to identify here this moment. If we take into account the bulk of epiclastic material, occurred subsequently as a result of the erosion of volcanic superst ruct ures together with the pyroclastic one proceeding from the explosive destruction of the latter, we have to reach the condusion that the sizes and number of volcanic apparata have been very large. The destruction of volcanic superstructures has probably begun very soon after their building, and the material resulted has eonstituted in its close vicinity the volcano- sedimentary formation. The surface of volcanic islands has considcrably increased, in some regions their joining to the land zone and the forming of small-sized intermountain lacustrine basins having probably taken place (plate and fig. 1, moment 3b). The genesis of the volcano-sedimentary formation cannot be con- ceived without the existence, at least parțial, of an aquatic cnvironment : if the destruction of volcanic structure» was caused by a subaerial erosion, the deposition of the epi- and pyroclastic material has occurred, to a greaț extent, under subaquatic conditions. The deposits from the basal and middle parts of the volcano-sedimentary formation comprises hori- zons wh.ose subaquatic sedimentation my be considered as doubtle.ss; this fact- signifies that its building had begun previously to the retreat of the Pannonian Basin waters when either the waters of this basin or locally those of smaller basins closed by volcanic heights covered this region. On the other hand, the petrographic features of deposits from the upper and partially middle part of the volcano-sedimentary forma- tion ascertain that the processes have been developing in a subaerial regime. Institutul Geological României PALEOGEOGRAPHICAL RECONSTTTUTION DURING THE NEOZOIC VOLCANISM 83 The destruction of volcanic apparata and the genesis of volcano- sedimentary formation had presumably occurred during a rather long time interval in comparison with the previous stage of volcanic activity. The decreasse of the intensity in the volcanic activity, the intensifi- cation of the erosion and aecumulation of volcanic detritus have taken place progressively until a moment of some equilibrinm was reached. If we would attempt Io evaluate the time interval for which available indications as to the presence of a lacustrine regim are at our disposal — from the beginning of the volcanic activity up to the middle of the sedimentation of volcano-sedimentary formation— we could state that it had been longer than it is admitted by the present day paleogeographical reconstituiions. 11' the volcanic activity had begun under its peculiar forms concomitantly with the sedimentation of deposits front the base of the E Zone, fact that in our opinion is proved, the middle part of the volcano-sedimentary formation cannot tally with the uppermost one of the E Zone (the transition from the Pannonian s.s. to the Pontian) when, according to the Lithofacial Atlas 1 :2,000,000, a complete filling of the lake had taken place. All these processes have certainly required a longer time interval than that corresponding to the E Zone; although we cannot estimate all the arguments of a stratigraphic nature, never- theless, we have the feeling that the hypothesis as for the preser- vation of the lacustrine regime in the region of Călimani, Gurghiu and Harghita Mts must be accepted also subsequently to the end of the Pannonian s.s. The volcanic activity during the genesis of the volcano-sedimentary formation is characterized by the fact that — besides the general decrease of its intensity — from the production of large amounts of cinerite mate- rial it will pass to the supply of coarse material and, to a lesser extent, of lavas thus revealing a modification in the type of activity. In the interval between the Pannonian s.s. and the Quaternary the cinerite material is almost completely lacking in the deposits found outside, as well as those inside the Carpathian Arc; very large masses of coarse pyroclastics are, however, accumulated over the territory of the Căli- mani — Gurghiu — Harghita Chain. The areal distribution of deposits pertaining to the volcaho-sedi- mentary formation is very significant for the understanding of the accu- mulation mode of the elastic material. The distances of its migration have no probably exceeded some -10 km, being in most eases much more reduced. The clear-cut limit of the volcano-sedimentary formation west- Institutul Geologic al României 84 DAN RĂDULESCU 8 wards, and the fact that it is corresponding today to a conspicuous rupture of slope, point out that even from the beginning (in the moment of the subaquatic regime), the spreading of the volcanic material, parti- cularly westward has occurred up to a practically linear limit, parallel to the axial zone of the mountain chain. It is most probably that the loss of the transport capacity of lake waters was determined especially by the decrease of the bottom slope and that the present western limit of the volcano-sedimentary formation is marking the westward exten- sion of the quasi-horizontal region of the bottom. The gradual decrease of depth in the lake and the forming of a horizontal bottom in its peripheral part by accumulation of volcano-elastic material have contributed to maintain a low transport capacity of waters, and hence the dispersion limit of particles. Thus the region covered by the volcano- genous material has undergone a continuous height increase stressing the inițial subaquatic rupture of slope. The accumulation process has continued displaying the same general features in subaerial conditions determining the formation of a plateau sharply limited westward, but eastward joining, to a great extent, the lower parts of the mountainous zone consis- ting of crystalline schists (plate, moment 4 b). The draining of waters from this zone was made directly westward, towards the central part of former lake, through valleys carved into the surface of the plateau; however, it is not out of question, that in some points of this plateau prominences which represent obstacles in the east-westward way of the waster streams had been preserved. The end of the building of the plateau corresponds to a short break in the volcanic activity and the transition to a new type of activity. The resuming of the volcanism took place under exclusively sub- aerial conditions, probably by the re-opening of the same conduits for magmas in the axial region of the newly formed plateau. Owing to a dominantly effusive activity some large-sized apparata have grown. In some points the emissions of lavas came sooner to an end determi- ning a more simple petrographic constitution and allowing the beginning of erosion. In most cases the lava emissions — with essential minera- logica! changes — have continued a longer time period leading to the occurrence of a mountainous zone with altitudes exceeding 2000 m. As in the previous phase-and maybe even more pronounced—at the beginning isolated apparata or groups of apparata (plate and fig. 1, moment 5 a) did occur, which only subsequently were joining together either by their products or by newly formed apparata leading to the Institutul Geological României <) PALEOGEOGRAPHICAL RECONSTtTUTlON DURING THE NEOZOIC VOLCANISM 8’ formation of the mountain chain. The hydrographical network concen- trated in some more important water streams, which passed westward among the previously appeared volcanoes; later on, the connection with the central part of the Transylvania Basin is completely interrupted, and between the volcanic mountain chain and the Crystalline—Meso- zoic Zone, intermountain depressions wherein lakes occur, have formed. The elosing of the volcanic activity is proceeding in climatic condi- tions favourable for an abundant vegetation, which has attenuated the erosion processes. The present day aspect of the region is due to the occurrenee of some valleys cut into the mountain chain and through which waters of the intermountain basins were drained west- and south- ward (plate and fig. 1, moment 5 c). The table totalizes the varied so far presented informațional data; as it may be stated, in the evolution of various groups of considered phenomena discontinuities of different nature are individualizing. From the viewpoint of the paleogeographical aspect there exist, for the period under study 4 main discontinuities — determined by : (a) occurrenee of volcanic proeminence on the bottom of the lake in its peripherial eastern part, (b) occurrenee of the archipelago of volcanic islands, (c) retreat of waters and setting in of the subaerial regime (d) disappearance of the mountainous volcanic relief over this land, — and 4 secondary discontinuities within the 3 last stages of the paleo- geographical evolution of this region. They correspond — as it might be espected since it deals with determinant relationships between these phenomena — to the main discontinuities in the evolution of the volcanic activity and in the evolution of the genesis environments of geologica! formations over the territory under investigation. The same wide categories of phenomena have determined the evolution of the supply with elastic material (sources) whose discontinuities are likewise tallying with those of the paleogeographical evolution. The 5 stages which may be distinguished in the paleogeographical evolution of the region comprise the time interval from the beginning of the Pannonian s.s. and until nowadays : the only age limit whose position in the evolution of the volcanic phenomena may be accepted with a satisfactory degree of certainty is that between the C/D and E zones of the Pannonian. The stages are defined by the distribution of waters and land areas as well as by the relief of the territory. The genera] sense of the evolution consists in the growth of the land on the expense Institutul Geologic al României DAN RĂDULESCU 10 of an area initially covered by waters, as a resnlt of occurrence of volca- nic apparata and of filling of the basin. The forms of relief mark a rapid evolution in this time interval corresponding to a „formation — destruc- tion” cycle and covering the first half of a second one. The schematic profiles from the table attempt to suggest images which we could form as to the aspect of the region in the various stages of its evolution. REFERENCES F i 1 i p e s c u M. G. (1911) Problema vulcanismului extracarpatie. Hei'. Muz. Min. Geol. Univ. Cluj, 7. Rădulescu D. (1968) Observații asupra paleogeogral'iei teritoriului lanțului eruptiv Călimani—Gurghiu —Harghita în cursul Pliocenului. Slud. cerc. geol. geof. geogr. Ser. geol. 13, 1. Rădulescu D., Peltz S. (1970) Observații asupra paleogeografiei teritoriului lanțului eruptiv Călimani—Gurghiu —Harghita în cursul Pliocenului și Cuaternarului. II. Slud. cerc. geol. geof. geogr. Ser. geol. 15, 1. Rădulescu D. (in prinț) Considerații asupra cronologiei proceselor vulcanice neogene din munții Călimani, Gurghiu și Harghita. D. s. Inst. Geol. LIX/4. București. * » * (1969) Atlas litofacial 1: 2 000 000. VI. Neogen. Inst. Geol. București. ^7^ Institutul Geological României SUCCESSION OF GEOLOGICAL EVENTS IN THE CALIMANI - GURGHIU - HARGHITA AREA DURING THE VOLCANIC ACTIVITY DAN RĂDULESCU* Tentative Paleogeographicol Reconstitution of the Câlimani - Gurghiu - Harghito Area during the Neoxoic Volcanic Activity Imprim- Atei. Inst. Geologic ANUARUL INSTITUTULUI GEOLOGIC VOL- XLf Institutul Geologic al României IGR/ Redactori : MARGARETA PELTZ, FELICIA ISTOCESCU Traduceri: MARGARETA HÂRJEU Ilustrația: VIRGIL MTV Dai la cules; aprilie 1973. Bun de tipar; iunie 1973. Tiraj 1000 exemplare. Hirlie scrin I .4 70% 100156 a: Coli de tipar: 5,5 Comanda: 630 Indicele (ie clasificare pentru biblioteci 55 (058). Tiparul executat la întreprinderea poligraficii Informația strada Brezoianu 23-25. București. România. Institutul Geological României Institutul Geological României ACCORDING TO THE GEOLOGICAL MAP OF Suppiemented by DAN P. RADULE W/âCU d SăInSii? Dec/d em REGHIN 0R6HIENI Borzont o Cm mani oCoruffd VREA vania GOORHEL aSînhmbru Basalts (B) Hornblende - andesites (aam) ANUARUL INSTITUTULUI GEOLOGIC, VOL. XLI lava sive U and SERGIU PELTZ 1050 m ROMANIA Scale 1 : 200.000 Deposits of the volcano - sedimentary formation ani Mts GEOLOGICAL MAP OF THE Basaltic andesites (a B ) Pyroxene-andesites (apy) Hornblende-pyroxene-andesites (aam py) Diorites and microdiorites (8,|xS ) CALIMANI-GURGHIU-HARGHITA CHAINE (INCLUSIVELV BÎRGĂU Mls. AND PERȘANI M