INSTITUTULUI GEOLOGIC AL ROMÂNIEI ISSN 1453-357X Voi. 72 Part II Paper presented at the XVI Congress of the Carpathian-Balkan Geological Association (Viena, 1998) Institutul Geologic al României București 2000 Institutul Geological României GEOLOGICAL INSTITUTE OF ROMANIA Director General Dr. G. Udubașa Member of the Romanian Academy The Geological Institute of Roinania is now publishing the following periodicals: Romanian Journal of Mineralogy Romanian Journal of Petrology Romanian Journal of Mineral Deposits Romanian Journal of Paleontology Romanian Journal of Stratigraphy Romanian Journal of Tectonics and Regional Geology Romanian Journal of Geophysics Anuarul Institutului Geologic al României Memoriile Institutului Geologic al României Romanian Journals supersede "Dări de Seamă ale Ședințelor” and "Studii Tehnice și Economice", whose appari- tion goes back to 1910. 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(+40) 1224 2091, 224 15 30 Fax (+40) 1 224 04 04 e-mail UDUBASA@IGR.RO The editor has changed the name as follows: Institutul Geologic al României (1906-1952), Comitetul Geologic (1953-1966), Comitetul de Stat al Geologiei (1967-1969), Institutul Geologic (1970-1974), Institutul de Geologie și Geofizică (1975-1993), Institutul Geologic al României (since 1994). ANUARUL INSTITUTULUI GEOLOGIC AL ROMÂNIEI supersedes ANUARUL INSTITUTULUI DE GEOLOGIE ȘI GEOFIZICĂ. Scientific Editors: G. Udubașa, S. Veliciu Advisory Board: Em. Antonescu, Tudor Berza, I. Hârtopanu, M. Mărunțiu, G. Udubașa The manuscripts should be sent to the scientific editor and/or executive secretary.- Correspondence concerning advertisments, announcements and subscriptions should be sent to the Managing Editor. ©GIR 2000 ISSN 1453-357X Classification index for libraries 55(058) Printed by the Geological Institute of Romania Bucharest Institutul Geologic al României CONTENTS Upper Pliocene Vegetational Phases South Pericarpathians Depression, Romania. E. Demetrescu .................................................................... 3 L'analyse du străin et ses implications pour l’etablissement des traces de la deformation dans les metaconglomerats paleozoYques des Monts Apuseni du Nord. M. Dimitrescu .................................................................. 9 40Ar -39Ar Laser Probe Dating on Single Crystals from Trondhjemitic Dikes - Sebeș- Cibin Mountains (South Carpathians) - Romania. A. DoBRESCU, P. SM1TH ...... 29 Kimmeridgian and Lower Tithonian Sequences from East and South Carpathians - Romania. D. Grigore ............................................................. 37 Regional Tectonics as Inferred from Gravîty &: Geoidal Anomalies. D. Ioane, L. Atanasiu 47 Piemontite Porphyroids from Valea Seacă (Tulgheș Group, East Carpathians, Romania) - Evidence for a Fault-Related Metasomatism. M. Munteanu, Șt. Marincea ............................................................. 55 Some Aspects Regarding Morphological Variations of Zircon Crystals from Muntele Mic Massif, South Carpathians-Romania: Petrogenetic Implications. I. N. Robu, L. Robu ......................................................................... 59 The Enclaves in the East Carpathian Neogene Intrusions (Romania): their Significance for the Genesis of the Calc-alkaline Maginas. E. Nițoi, M. Munteanu, Șt. Marincea .................................................................... 67 Njgr Institutul Geological României Institutul Geological României An. Inst. Geol. Rom., 72. part. II, p. 3-8, București, 2000 UPPER PLIOCENE VEGETATIONAL PHASES SOUTH PERICARPATHIANS DEPRESSION, ROMANIA Emanuel DEMETRESCU Geological Institute of Romania, 1 Caransebeș St., RO-79678 Bucharest 32 • Key words: Palynostratigraphy. Upper Pliocene. Romania. Abstract: A detailed succession of ten palynologic assemblages consisting of pollen and spores and freshwater cysts is presented. All morphotypes have been delivered along the South peri-Carpathians area during a period of time when most of the tardy Magnoliophyta families have started their development. Based upon their distribution and paleoenvironmental significance during the Upper Pliocene, a ten-level palvnos- tratigraphic scale of specific occurrence is proposed. Introduction The material has been collected from eight sections (Fig. 1), and consists of dark to light grey clays and coaly clays. The palynologic characterization is based upon ten groups of pollen and spores delivered from land- growing taxa, plus a suite of four spectra predominantly encompassing pollen of both emergent and submerged aquatic plants. All are regarded as assemblages rather than ”associations” to stress upon the absence of biostratigraphic markers. This mode of viewing things has been carried by the fact that the growing of vegetation has been tributary - at least in this area - to environmental and depositional instead of biostrati- graphic control. Owing to high vertical and horizontal fluctuations from one site to another as an effect of sedimentary conditions in alluvial plains, there is not a single taxon as reliable for biochronostratigraphic purpose as necessary. It goes without saying that, under the circumstances, one cannot establish a strati- graphic scale in terms of ISG recommendations but solely resume to present these groups as they succeed in the studied deposits. The respective assemblages (aquatics included) define fourteen intervals or levels (Table 1), ea.ch having a particular reproducible degree (RD). This attribute has been assimilated after that referable to biochrono- logical associations (Geux, 1987) yet bears no sucii a significance in the case here discussed. As seen in Table 1 eight spectra can be grouped to result eventually only ten characteristic assemblages or "palyno-levels" whose position is labelled base upwards. Some of these taxa have a. restricted occurrence, others extend throughout the whole area and severa! out of those recovered from the upper interval make up assemblages that interpenetrate with one another vertically and show a discontinuous distribution laterally. Palynologic delimitation based on these levels of occurrence is illustrated in Figure 2. Discussion The suite of vegetational phases starts with a very diversified spectrum predominantly arboreal repre- sented by a remarkable gymnosperm and angiosperm assemblage. It has been recovered from the lower third of the Parscovian sub-stage and represents the so-called Tertiary relics. Cedrus, Taxus and Ketelee- ria should be mentioned amongst Gymnospermae. Taxodiaceae have delivered Glyptostrobus europeus and Cryptomeria sp. Pollen of Sequoia also occurs in relative high percentage. The content of humic substances at this level documents the existence of an environment rich in humic clays for which Sequoia trees are supposed to have a high affinity. Other morphotypes indicative of warm climate are Sciadopitys, Tsuga and Ginkgo. Angiospermae include Symplocos, Nyssa, Catalpa bignonioides, Liquidambar, Carya, Ptew- carya, Myrica and the liana Parthenocissus. Broad-leaved forms such as Castanea and other Fagaceae have had an important participation, Castanea particularly suggesting coasta! low land forests. The couple Institutul Geological României 4 E. DEMETRESCU Fig. 1 - Sketch map showing the studied area sampled sections; columns are not at scale. Institutul Geological României l'PPER PLIOCENE VEGETATIONAL PHASES 5 Table 1 Levcls C h a r a c t c r i s t i c assemblages RD Sections Leadingtaxa and/or indicative group Main constituents (besides leading species) 10 Ai1eniisia-Selaginella Polygala, Graminac, div. inosscs spores 2 2,5 Aquatics IV - Pediastrum other I lydrodyctiaccac and Zygneinataceac 9 Spergularia-Gypsophila Ilibiscus, Puplemm, ?I'~ilipemhila, Polygala 4 1-3, 5 8 /leacia-Olcaceac Jasminum, Syringa, Ligustnim, Olea, Fraxinus. Aesculus, Rhns 5 1-3, 5,7 7 Shrubs DI Myricaria, Taniarix, Spirea. Staphylea 1 7 6 Aquatics IU - Dtriculana Potamogeton, Nelumbo, Menyanthes, Sagittaria, asperula, Nymphoides, Nymphaea, Nuphar 4 1,4, 5,7 Aquatics 11 - Stratiotes Heleochans, Hydrocharis, Pamassia, EpUobiuni. Pedicidaris 5 1,3-5,7 5 Shrubs 11 Lonicera, Sambucus, Fibumum, Eleagnus Crataegus, Corylus, Alnus, 2 5,7 4 Cuprcssaceac- Taxodiaceac I’inaceac Larix, Juniperus, Picea, Bclulaccae, /ker 4 1,3, 5, 7 I lerbs & Bushcs Dipsacus, Polygonum, Rumex, Halva, Geranium 3 1,3,5 3 Aquatics I Lysiniachia, Myriopltyllum, Geranium ?paluslris, Ealrachium, Ceralophyllum, Azolla, Salvinia, Zygnemataccac 3 1,3,5 2 Sphagnum-Drosera l’leridophyta and fungi 5 1,3,5,6,8 Shrubs I - Ericaceae Salix, Carex, Phragmiles 7 1-6,8 1 Tertiary rclics Ginkgo, Keteleeria, Cathaya, Tsuga, Taxodium, Glyptostrobus, Sciadopyfis, Symplocos, Liquidambar, ('an’a. Pțerocarya 7 1-6,8 Symplocos-Nyssa may indicate high groundwater table. The humid conditions are also reflected by the occurrence of Sequoia-Taxodium-Sciadopitys all standing for wetter and warmer climate. Symplocos also docmnents the existence of Mediterranean and paleosubtropical conditions. It could have not developed if the winter temperature would have not been well above 0°C. Towards the upper part of this interval a dilution in the constituency of this first assemblage has been observed. This is consistent with the trend ofswitching toward ashrubbery phase with Ericaceae, Salicaceae and Myrica that followed above and characterizes the second group of this succession. All environmental conditions have changed, the palynologic spectrum becoming more scarce. The advent of Ericaceae may stand for a reduclion in nutrient supply and the existence of more drained soils. The climatic deterioration is also suggested by the presence of Corylus and the following Sphagnum-Drosera couple accompanied by Pteridophyta and fungal remains consisting of various ascospores and hypae. The most remarkable taxon out. of this assemblage is Drosera, which indicates the development of peat-forming bogs. Institutul Geological României fi E. DEMETRESCU UPPER PLIOCENE VEGETATIONAL LEVELS 1 Lupoaia 2 Miculești 3 Peșteana 4 Ruget 5 Târâia Valley 6 Well 27 Moșteni 7 Sânger Valley 8 Filipeștii de Pădure IARTEMISÎA-SELAGINELLA AQUATICS IV ACAC/A-OLEACEAE AQUATICSII & III JSHRUBSII HERBS& BUSHES (AQUATICS I SPHAGNUM-DROSERA SHRUBSI TERTIARY RELICS © Fig. 2 - Stratigraphic delimitation based upon palynomorph distribution according to Table 1. Institutul Geological României UPPER PLIOCENE VEGETATIONAL PHASES 7 The third phase chiefly characterizes a more humid habitat with aquatics sensibly increasing. In additioji to very well preserved massulae of Salviniaceae a suit of aquatic morphotypes of both lacustrine and riparian habitat do occur at. this level. Pollen derived from other plants is not- particularly significant and accumulated during a period of time when the pollen rain dropped from more distant, arboreal taxa, thus from extra-local sources (e. g., Pinaceae, Fagaceae and Juglandaceae). The material from the immediate overlying intervals suggests a relative decline in the climatic regime, with two assemblages which mix up with one another: they are herbs and bushes and Cupressaceae-Taxodiaceae- Pinaceae group. The palynocontent is dominated by Picea. Larix and Juniperus to which add Pinus and Abies. Juniperus possibly had a scattered distribution. It generally grows on elevated sites and the fact that pollen of this taxon, not exceeding 9 %, does persist in this interval accounts for our supposition that cooler conditions either have existed at regional scale or have functioned as micro-climate. After all the whole assemblage seems to suggest the existence of such a climatic regime and is consistent with the presence of herbs and bushes continuing their development from the underlying interval. For all that, this community out of which the deciduous taxa are almost. missing (Fagaceae 1.8 %, Juglandaceae 0.0 %, Tilia, Celtis and Ulmus between 0.7 and 1,2 %) does not indicate necessarily a deterioration of climatic conditions. Jacobson (1979), studying the paleoecology of Pinus strobus (White Pine) has shown that an increasing in accumulation of pine litter increases soil acidity which reduces, in turn, the bacteria! decomposition and ultimately acts like a barrier stratum for other seeds which can no more reach the mineral soil and germinate. It is reasonable to assume that a similar mechanism might also had taken place in relationship with other coniferous types producing heavy litter accumulation which possible has led to such a situation in this area. In the case of this particular level the possibility of transport from outside the sector is not considered, primarily due to the coherence t he respective assemblage shows. Erdtman (1969) has stated that Picea produces pollen grains with high settling velocity which are not dispersed far from the source. Further on, following a short and passing shrubbery phase (Shrubs II), during which no noticeable event has been remarked, the depositional area must have suffered a strong subsidence as proved by a sudden advent of submerged lacustrine representatives of the Aquatics II and III, respectively. They characterize much deeper environments and have been accompanied by riparian hydrophylous types. It is pointed out the particular significance some species have for they release their micro-organs directly into the water. It is the case of Straliotes, Heleocharis and Hydrocharis, all belonging to the Aquatics II assemblage. Such pollen possesses a very thin exine and their well preserved state demonstrates beyond don bl that the whole organic fraction has not been removed after settling nor has been strongly affected after settling. One can consider the respective occurrence as being highly indicative from both stratigraphical and paleoenvironmental viewpoints for it documents the existence of a unique interval of distribution plus the fact that the deeper lacustrine habitat has covered much larger sectors. With this aquatic inter-phase the sequence of Upper Dacian (Parscovian) comes to an end. What follows above beginning with Shrubs III belongs to the Romanian stage and characterizes its first sub-stage: the Pelendavian. Most of the taxa here still have the riparian status but some have certainly inhabited the floodplain area. In terms of vegetation change this populat.ion of shrubs and sub-arboreal species characterizes an interval of transition toward more arid and warm a climate. Although the percentage value of Tamarix and Myricaria is rather low (2 % and 4 % respectively), one should not overlook that they are entomophylous species and this suggests a controlled dispersai from local sources. Farther on the development of Acacia - Oleaceae merely confirms the existence of warmer climatic con- ditions. Desiccation has accentuated the attributes of open land environment which has favoured the con- tinually reducing process of the depositional zone during which the organic particles have suffered a more intense degradation. Through time the aridity has increased and the main taxa likely to inhabit and compete under such conditions have mostly been herbaceous as it is documented by the occurrence of Spergularia - Gypsophila couple plus some Fabaceae and composits. This situation went on this way until a new phase of fluvial regime has been initiated. The fluvial activity led to a slight development of frewshwater algae and especially Hydrodyctiaceae (Pediastrum). The presence of micro-organs delivered from wild-growing herbaceous vegetation plus the occurrence of Artemisia and its relatives prove the existence of an area. mostly deprived of arboreal taxa, while Selaginella implies the existence of high peat bogs. In terms of paleoclimatic modification a visible change toward more sensibly deteriorating conditions has taken place. 'A Institutul Geological României 16 R A E. DEMETRESCU $ Conclusions A prime inference ensuing from this study is the fact that continental palynomorphs of Pliocene age, though inadequate for bringing about proper stratigraphic characterizations, may nevertheless offer a reliable background of research even though restricted to local scale. In terms of vegetation growing, it may be said that during the Parscovian a range of successive phases has developed, making up, on the whole, a more diversified spectrum out of which some taxa show strong ( aspian and even Far East influences. In marked contrast, the following succession appears more limited aiul includes shrubs and trees only at the beginning of the Romanian, a period of time during which some Mediterranean species have found propitious ambiency to develop. Both are the consequence of a mixed development of paleosubtropical and arcto-Tertiary species. Whereas the Parscovian is characterized by all types of vegetation compatible with a variety of environments and Controls, during the Romanian especially wild-growing herbs have characterized the inhabiting vegetation. References Demetrescu, E.. (1993) Palynostratigraphic levels in tbe Dacian stage from Romania. Rev.Roum. Geol., 37, p. 95-99. (1995) Studiul palino-sedimentologic și palino-stratigradc. Potențial și aplicabilitate. Cazul sedimentelor pliocene din avanfosa Carpaților Meridionali. Doctorate thesis (in Romanian), Univ. Bucharest, 386 p., unpublished. Erdtman, G. (1969) Handbook of palynology, Morphology-Taxonomy-ecology. Munksgaard. Genx. J.. (1987) Correlations biochronologiques et associations unitaires. Univ. Lausanne, 249 p. Jacobsou, G. L. (1979) The palaeoecology of White Pine (P. strobus) in Minnesota. Jour. Eco/., 67, p. 697-726. An. Inst. Geol. Rom., 72, part. II, p. 9-27, București, 2000 L’ANALYSE DU STRĂIN ET SES IMPLICATIONS POUR L’ETABLISSEMENT DES TRACES DE LA DEFORMATION DANS LES METACONGLOMERATS PALEOZOIQUES DES MONTS APUSENI DU NORD Mihaela DIMITRESCU Institutul Geological României, str. Caransebeș nr. 1, RO-79678 București 32 Key words: Metaconglomerates. R//o technique. Plane străin. Coaxial deforma- tion. Abstract: Străin analysis and its irnplications for the determination of deformai ion paths in the Paleozoic metaconglomerates of the Apuseni Mountains. In the Northern Apuseni Mountains, the presence of stretching lineations of pebbles in metaconglom- erates and the angle between the schistosity and the boundaries of the nappes suggest that. during the deformation, a component of the shearing străin was active. The străin rate (R.) and its orientations (©') in the bi-dimensional planes were deter- mined only on the basis of measures in the metaconglomerates. The data of the three principal perpendicular planes were combined in order to determine the finite străin ellipsoidal in 10 localities. The finite străin was decomposed into two components, the simple shear one (7), and the pure shear one (A), which were determined directiv on the 0’/R diagram. The collected data show that the observed deformation can- not be explained exchisively by simple shear, but rather by an association of simple shear with longitudinal străin. The combination of finite deformation with the time necessary for its accomplishment leads to the approximation of the mean străin rate at values comprised between 0.32 and 2.19X10-14 s-1. Introduction Les Monts Apuseni du Nord ont commecaracteristique lastructure en nappes de charriage constituees par des formations cristallines precambriennes-cambriennes recouvertes par des depots sedimentaires permiens- mesozdfques. Pour connaitre plus en detail les mecanismes des charriages il est. necessaire de rassembler des donnees quantitatives concernant les modifications internes eprouvees par les nappes. Dans la region etudiee, les reperes du străin (de la contrainte) peuvent etre trouves dans les roches metasedimentaires (conglomerats, greș, argiles) ou dans les breches tectoniques. Nous n’avons pris en con- sideration que les conglomerats metamorphises des nappes de Garda, Poiana, Biharia et Highiș. lls ont ete etudies en 10 points d’observation situes dans les zones d’affleurement aussi bien de la Formation des (‘onglomerats Lamines de la Nappe de Garda que de ses equivalents dans les autres nappes, notamment la Serie de Poiana pour la Nappe de Poiana et la Serie de Păiușeni pour les Nappes de Biharia et de Highiș (Olaru, DimiCrescu, 1994). Les roches soumises â l’observation sont d’age Carbonifere superieur-Permien inferieur et ont soufert une deformation faible a moyenne, visible grâce au contraste de viscosite qui a genere le comportement â la contrainte nettement different des galets par rapport â la matrice. Le but du present travail consiste en la determination des effets du charriage de Faccumulation de nappes pendant le Turonien, â l’aide de l’analyse du străin des galets dans les conditions de la modification de leur forme mais non pas de leur volume et en l’absence de la dissolution sous pression. Nous avons aussi cherche a determiner le taux du străin, quelques elements de cinematique des zones de charriage, la variation du străin dans les nappes etudiees ainsi que les traces parcourus au temps de la deformation par les reperes choisis. Institutul Geological României M. D1MITRESCU Fig. 1 I. ANALYSE DU STRĂIN ET SES IMPLICATIONȘ 11 Fig. 2 - Diagramme R^/e. a) Valea Negrii; b) Cascade du Vârciorog; c) Piatra Molivișului; d) Izvorul Arieșului Mic: e) Forteresse de Șiria. Institutul Geological României 12 M. DIMITRESCV Analyse du străin Les mesures des rapports axiauxet de Torientation des galets dans les metaconglomerats ont ete effectuees eu 10 points d’observation ayant la distribution suivante dans les differentes unites tectoniques: Bricești, Valea Negrii (Nappe de Garda); Cascade du Vârciorog, Pârâul Corbului, Valea Plaiului (Nappe de Poiana); Piatra Molivișului, Valea Bucegița, Izvorul Arieșului Mic (Nappe de Biharia); Forteresse de Șiria, Valea Sălăndașului (Nappe de Highiș). Leur localisation sur l’esquisse geologique est montree dans la Figure 1. 1. Analyse du străin bi-dimensionnel La technique de travail adoptee pour l’analyse 2D (bi-dimensionnelle) de la contrainte a ete decrite en deta.il dans d’autres travaux (Dimitrescu, 1995, 1997), nous n’allons plus insister sur elle. Nous considerons toutefois necessaire de faire quelques remarques sur la methode Ry/p. Denommee initialement methode Ramsay-Dunnet, elle a ete modifiee par Ies ameliorations proposees par Lisle (1977), en arrivant aujourd’hui ă etre la technique la plus utilisee, avec plus de cent applications decrites dans la litterature. Des etudes comparatives entre les diverses methodes d’estimation du străin tectonique (Hanna, Fry, 1979; Siddans, 1980; Paterson, 1983: Lisle, 1985) il resulte que en dehors de sa large applicabilite, la technique Ry/O est aussi une des plus precises. Le principe de la methode consiste en l’evaluation des distributions initiales des galets par le retour â letal anterieur au străin mesure, en procedant par la superposition d’une contrainte coaxiale ă l’axe long â 90° de Porientation preferentielle des galets. Sa magnitude est reduite successivement. en calcnlant apres chaque pas combien aleatoires sont les orientations des galets de moins en moins deformes. Si init ialement il n’a existe aucune orientation preferentielle, on peut calculer la valeur du străin fini (R,) necessaire â la realisation de la distribution la plus uniforme des galets. Les donnees recueillies dans le terrain ont ete operees ă l’aide du programme THETA pour ordinateur, elabore par Ratschbacher et al. (1994) d’apres le modele plus ancien de Peach et Lisle (1979), les valeurs des parametres determines etant presentees dans le Tableau 1. Nous devons preciser que la mesure de la fluctuation des galets n’a pas ete possible dans tous les points d’observation (p ayant parfois des valeurs voisines de zero), et en consequence le calcul n’a ete fait que pour cinq affleurements. En comparant Ies diagrammes Ry/p de la Figure 2. nous avons constate que ceux correspondant aux points Valea Negrii, Izvorul Arieșului Mic et Forteresse de Șiria presentent une legere symetrie. Cel aspect pourrait etre du ă Eexistence d’une orientation preferentielle des axes longs des galets generee par la symetrie des distributions pre-tectoniques. Tableau 1. Donnees du străin 2D Nr. Localisation N. Rf Ri Rs V 1 Valea Negrii 46 1,79 1,34 1,64 1,50 2 Cascade du Vârciog 31 1,87 1,53 2,07 0,80 3 Piatra Molivișului 21 2,52 1,74 2,97 1,00 4 Izvorul Arieșului Mic 46 1,97 1,80 2,02 2,00 5 Forteresse de Șiria 60 1,72 1,46 1,62 0,50 Pour approfondir ce probleme nous avons utilise une autre serie de diagrammes concus par Lisle (1985), qui montrent les traces suivis par les galets au temps de leur transformation de l’etat inițial (Rf, 0) â letat final (Ry, p) quand entre les galets et la matrice il existe un contraste de viscosite. Afin d'expliciter les diagrammes, nous precisions qu’au cours de la deformation, les galets sont soumis â une rotation vers la direction principale d’extension, chaque galet se mouvant le long d’un trace propto (ligite â 0 constant) vers la. gauche (vers de petits angles p). En general les formes des distributions finales sont symetriques, ainsi qu’on peut le constatei- en suivant les contours traces sur les diagrammes de la Figure 3. Theoriquement, dans les conditions speciales de lacombinaison des variables străin et distribution inițiale, la symetrie des projections Ry/p peut provenit de: Institutul Geological României LANALYSE DU STRĂIN ET SES IMPLICATIONS 13 PHI.THETA PHI.THETA Fig. 3 Traces ele la deformation par cisailletnenl pur potir divers contrastes de viscosite. a) Valea Negrii: b) Cascade du Vârciorog; c) Piatra Molivișului; d) Izvorul Arieșului Mic; e) Forteresse de Șiria. Institutul Geological României 14 M. DIMITRESCU 1. distributions initiales symetriques, qui ont ete deformees par une contrainte superposee symetrique, comme dans le cas des points Valea Negrii et Forteresse de Șiria; 2. distributions initialement asymetriques, sur lesquelles s’est superpose un străin oblique, situation possible ă Izvorul Arieșului Mic. Malgre nos efforts de dechiffrer les causes theoriques de la symetrie des diagrammes R//0, il faut re- connaître que nous ne detenons pas encore toutes les observations de terrain necessaires ă une etude sur la rotation des galets rigides dans leur matrice ductile, pour pouvoir etablir avec precision si l’orientation des galets peut etre attribuee aux proces primaires de deposition, au străin ou ă un mecanisme de rotation des clastes dans la roche noh lithifiee. 2. Analyse du străin tri-dimensionnel La meilleure geometrie pour la determination de Pellipsoide du străin â partir de trois sections se presente lorsque celle-ci coincident avec les trois plâns principaux de l’ellipsoîde. On peut alors aflinner que les axes principaux sont mesures directement. En tenant compte de ces exigences, pour obtenir les valeurs et les directions du străin fini en trois dimen- sions (3D), nous avons combine les donnees de trois sections planes perpendiculaires ou quasi-perpendiculaires entre elles. L’ellipsoîde du străin a ete calcule â l’aide du programme pour ordinateur conțu par Milton (1980) et repris plus recemment sous la denomination de TRISEC par Ratschbacher et al. (1994). Les donnees primaires demandees par le programme sont: l’orientation des trois plâns, la fluctuation moyenne des ellipses mesurees sur chaque section et le rapport axial final moyen calcule separement pour chaque plan. L’annexe 1 comprend les resultats de l’analyse effectuee pour la determination de la longueur et de l’orientation des axes principaux de l’ellipsoîde de deformation dans les points d’observation: Bricești, Valea. Negrii, Cascade du Vârciorog, Pârâul Corbului, Valea Plaiului, Piatra Molivișului, Valea Bucegița, Forteresse de Șiria et Valea Sălăndașului. A la base de la methode proposee par Milton reside l’observation suivante: dans le cas d’une contrainte bomogene, les ellipses mesurees sur trois sections quelconques doivent. idealement etre compatibles si celle- ci appartiennent, au meme ellipsoî’de de străin. Mais quelques inconsistances, comme seraient les erreurs d’observation, l’inhomogeneite de la contrainte dans l’affleurement ainsi que la variation de la position des sections planes en rapport avec les axes principaux du străin, font obligatoire la correction des ellipses du străin â l’aide d'un facteur d’ajustement pour les rendre compatibles (c’est â dire pour pouvoir les considerer comme appartenant au meme ellipsoî’de). Le facteur d’ajustement correspond au rapport axial de 1 ’ellipse du străin d’ajustement qui se superpose au străin mesure (Milton, 1980). En revenant ă l’analyse effectuee, nous constatons que les valeurs les plus elevees du facteur d’ajustement oul ete calculees pour les points Piatra Molivișului (4,14) et Pârâul Corbului (1,72). On est meme arrive â ia situation que ă Valea Negrii les trois surfaces mesurees n’appartiennent pas ă un ellipsoî’de mais ă un hyperboloîde (Annexe 1). En echange, les valeurs reduites du facteur d’ajustement pour tous les autres points d’observation mon- trent le fait que, d’une part, les ellipses mesurees appartiennent au meme ellipsoî’de, le străin d’ajustement. necesaire â la realisation de la compatibilite des sections etant de magnitude reduite, et que d’aute part, le plan XY coincide avec ou est tres approche de la direction X du străin. Les directions principales du străin et les valeurs X/Z de l’ellipsoîde de la deformation sont projetees sur les coupes geologiques de la Figure 4 qui presentent la geometrie ă moyenne echelle de la region etudiee. L’explication que nous acceptons ă present dans le cas des points Piatra Molivișului et Pârâul Corbului ou la direction de la contrainte differe de l’orientation du plan XY, est que dans les affleurements respectifs la deformation a eu un caractere non homogene. Institutul Geological României L'ANALYSE DU STRĂIN ET SES IMPLICATIONS 15 En conclusion. l'orientation des ellipses du străin de la plus grande pârtie des coupes geologiques presenlees dans la Figure 4. refiete le străin fini produit par la meme phase de deformation, commune ă tous les points d’observation. Resultats du străin fini Tont străin fini resulte de l’accumulation de ses accroissements dus aux phases de deformation qui se sont succedees. Ramsay (1967) a montre que pour effectuer l’analyse de la deformation il est necessaire de la decomposer en deux composants lies au străin non-rotationnel (produit par cisaillement pur) et au străin rotationnel (produit par cisaillement simple). En ce qui suit nous allons essayer d’etablir les relations entre la variation du străin de cisaillement.et les mouvements des nappes de charriage. Toutes les donnees du străin fini ont ete projetees sur un diagramme logarithmique de la deformation (Fig. 5) pour suivre la variation de la forme de l’ellipsoîde du străin. Les ellipsoîdes de type aplatissement et allongement sont separes de ceux du străin plan par la ligne Ej- E2=E2-E3+ln (1+A), ou A est la modification du volume et E1j2,3 representent les contraintes principales finies logarythmiques (Ramsay, Wood, 1973). Les valeurs du parametre k=(Ei-E2)/(E2-E3) se trouvent dans le Tableau 2. Tableau 2. Parametres de la forme des galets Nr. Localisation Er e2 e3 K 1 Bricești 0,67 - 0,16 - 0,55 2,07 2 Valea Negrii 0,80 0,23 - 0,92 - 0,50 3 Cascada Vârciogului 0,64 - 0,04 - 0,59 1,25 4 Pârâul Corbului 0,22 0,05 - 0,46 0,33 5 Valea Plaiului 0,95 0,04 - 0,83 1,04 6 Piatra Molivișului 0,86 - 0,20 - 0,70 2,08 7 Izv. Arieșului Mic 0,70 - 0,07 - 0,63 1,37 8 Valea Bucegița 1,12 0,01 - 1,01 1,10 9 Cetatea Șiria 0,47 - 0,14 - 0,35 2,86 10 Valeâ Sălăndașului 0,51 - 0,16 - 0,48 2,06 La plupart des projections se situe dans le champ de l’allongement, mais seulement les points Bricești. Piatra Molivișului et Forteresse de Șiria s’eloignent de la ligne du străin plan. Dans l’autre champ sont emplaces les points Valea Negrii et Pârâul Corbului. Leur position par rapport â la ligne du străin plan peut etre expliquee comme resultat des deux suivants processus differents: 1. allongement physique en direction d’Y; 2. superposition d’une contrainte homogene sur une contrainte plane (Ramsay, 1980). Si Peloignement de la ligne k=l (et A=0) est du entierement a l’extension suivant Y, des modifications considerables de l’axe Y, entre 50 % et 250 %, sont â attendre. Comme tels allongements n’ont. pas ete mis en evidence ni dans le terrain, ni par calcul (Dimitrescu, 1997), l’examen de l’autre hypothese s’impose. La deviation ă partir du străin plan peut resulter d’un cisaillement simple ou d’une combination entre un cisaillement simple et un străin longitudinal (Ramsay, 1980). Pour le cisaillement simple on peut. etablir une relation entre l’orientation de l’axe principal de l’ellipse du străin (0’) par rapport avec la marge de la zone de cisaillement et le rapport du străin (RJ, relation decrite par une courbe du type reproduit en Figure 6. L’appreciation des angles entre les grands axes des ellipses du străin et les fronts des nappes n’a ete possible que dans 6 points d’observation, ainsi qu’il resulte du Tableau 3. Nos donnees projetees sur le diagramme de la Figure 3 ne se posent pas sur la courbe, et on peut donc tirer la conclusion que le străin fini observe n’est pas du exclusivement au cisaillement simple, ni â l’allongement parallele ă l’axe principal X, mais â la combinaison des deux deformations. Institutul Geological României 16 M. DIMITRESCU Tableau 3. Parametres du străin de cissaillement Nr. Localisation 0’(o) Rs A 7 1 Bricești 5 2,09 2,00 0,25 2 Valea Negrii 20 2,15 1,50 0,75 3 Cascada Vârciogului 5 1,88 1,85 0,25 4 Pârâul Corbului 10 2,08 1,85 0,50 5 Valea Plaiului 17 1,28 1,25 0,25 6 Piatra Molivișului 5 2,13 2,10 0,25 Mathews et al. (1971) ont montre que la contrainte finie peut etre decomposee en un străin de cisaillement (7) en direction du cisaillement et un străin longitudinal (A) en direction de l’axe principal X. A l’aide du diagramme conșu par Coward et Kim (1981), reproduit en Figure 7, on peut determiner les parametres 7 et A en fonction de Rs et 0’, sans prendre en calcul la diminution de volume (△). Tout.es les valeurs du străin longitudinal determinees graphiquement (Tab. 3) sont supraunitaires, ce qui conformement aux observations de Coward (1976) et Kligfield et al. (1981) refleterait un amincissement des zones de cisaillement. En faveur de cette idee plaiderait aussi la distribution des points sur le diagramme Flinn (la plupart dans le champ de Textension), qui d’apres l’opinion de Ramsay et Allison (1979) indiquerait la presence d’une pârtie terminale des zones de cisaillement. Du groupement evident des points d’observation dans le champ du cisaillement pur (Fig. 7), on peut deduire le fait que, bien que des nappes de charriage diflerentes ont ete etudiees, la deformation produite sur leur entiere aire de developpement a eu un caractere homogene, exprime par l’allongement de l'axe principal X de Eellipsoide du străin dans la direction d’avancement des nappes. Une autre hypothese ayant trăit aux valeurs tres basses du străin de cisaillement (Tab. 3) serait aussi possible, valeurs qui suggerent le role reduit du cisaillement simple par rapport au cisaillement pur. Sans tenter une separation nette entre les domaines de manifestation des cisaillements simple et pur, mains, au contraire, en les traitant toujours ensemble, nous avons illustre dans la Figure 8 les nombreuses sequences intermediaires. Bien que nos points se projettent dans le domaine du străin longitudinal, l’aspect de continuite ne peut pas etre ignore dans le champ delimite par les courbes a accroissement de la rotation (u>) â partir de 0,00 (cisaillement pur) jusqu’â 5,45 (cisaillement simple). L’obtention du nombre le plus eleve possible de donnees concernant l’histoire du străin rend inevitable une reponse â la question si le străin sectionnel a un caractere coaxial ou non-coaxial. Lisle (1986) a demontre mathemathiquement le mode de determination du caractere du străin sectionnel dans le cas ou ies plâns mesures sont choisis rigoureusement paralleles aux plâns principaux de l’ellipsoide de deformation. Tableau 4. Donnees de la deformation combinee coaxiale et. non-coaxiale Nr. Localisation Ei e2 e3 K 1 Bricești 2,60 0,57 2,58 2,40 2 Valea Negrii 2,17 0,65 3,42 1,80 3 Cascada Vârciogului 4,71 0,29 2,43 2,53 4 Pârâul Corbului 2,19 0,36 1,27 4,43 5 Valea Plaiului 7,93 0,18 3,52 1,30 6 Piatra Molivișului 2,75 0,59 3,93 1,60 7 Izv. Arieșului Mic 3,81 0,38 2,77 2,23 8 Valea Bucegița 14,38 0,12 7,92 1,00 9 Cetatea Șiria 2,13 0,65 1,80 3,33 10 Valea Sălăndașului 2,17 0,60 1,93 2,43 Etant donne que cette condition est remplie (Dimitrescu, 1997), nous avons projete les 10 points d’observation sur le diagramme realise par Lisle (1986), dans lequel les axes de coordonnees sont notees de la maniere sui- !. ANALYSE UT STRĂIN ET SES IMPLICAT10NS 17 200 m I______I 18 M. DIMITRESCT F' 600 100 200 0 • 200 -«.00- • 600- Unite de Finiș Nappe de Highiș 5.66 <1 ^R & & 6 O Qtjț) O5" O tl $$ $ țl ti $ Q * O 51 « O Q Q ________ .- 1 ți Q țl ți <1 V * ți^^^^ • ioooJ v.Sâ{ândoș 278 2OOm Fig. 4 - Conpes geologiques dans la region etudiee avec l’indication des rapports X/Z des ellipsoides de străin. Institutul Geological României I. ANALYSE DU STR.A1N ET SES IMPL1CATI0NS 19 LEGENDE - Fig. 4 — Depâts quaternaires Systeme des nappes de Biharia Nappe de Muncel-Lupsa E^3 Porphiroides — Schists sericiteux + - + - ! •• - - - - * Metagranites gneissiques — Schists chloriteux a porphyroblastes d'albite Nappe de Biharia o o o o o Metaconglomerats — Schists chloriteux ă porphyroblastes d'albite Ecaille de Piatra Grăitoare o o a o o Metacong lome'rats • — . — Schists chloriteux a porphyroblastes d'albite Nappe de Highiș-Poiana O O O o o Metaconglomerats et schists quartzo-sericiteux Systeme des nappes de Codru Nappe d'Arieșem’ — Phyllites sericiteuses.gres Nappe de Finiș-Gârda Dolomies Quartzites 1 f t— 1 1 Porphy res O o O o O Congiome'rats lamines + ♦ 4 G ranites += += += Migmatites de Codru Signes conventionnels — Limite geologique Limite de discordance Limite du Quaternaire > ■ 1 ■ ■ ■ 1 Nappe de charriage 1—1—1—1 Ecaille -------- Faille Institutul Geological României 20 M. DIMITRESCU Fig. 6 - Projection du rapporl du străin (li) versus l’angle (®’) fait par le plan principal XY avec la surface frontale de la nappe (d’apres Coward et Kim, 1981). Fig. 5 - Diagramme Flinn des valeurs du străin des metaconglomerats des Monts Apuseni du Nord. Fig. " - Valeurs du cisaillement simple (lignes interrompues) el du cisaille- ment pur (lignes continues) projetees sur la carte de la deformation pour divers rapports (R) et orientations (0') du străin (d’apres Coward et Kim, 1981). Institutul Geological României ANALYSE DU STRAIE ET SES IMPLICATIONS 21 Orientation du străin fini t pri ncipal Fig. 9 Traces du străin en fonction des courbes V* (d’apres Lisle, 1986). Temps Fig. 10 • Diagramme des histoires possibles de ia deformation (d’apres Means et ai.. 1980). Institutul Geological României 22 M. DIMITRESCC Fig. 12 Les uuix du străin de risaillcmeni (simple e[ pur) correspondant ă certains interval les de temps (d'apres Pfiffner el Ramsay. 1982). I ig. I I Variaiion du străin de cisaillement. avec le străin naturel Ic long W/.>0 et qui correspondent aux deformations les plus frequentes de la geologie structurale. IGR I. A:\AI.YSE DL' STRĂIN ET SES IMPLICATIONS 23 Ramberg (1975) a montre qu’ă. la base des nappes, â cause de la friction avec le soubassement, apparaissent do cisaillements simples paralleles â la surface de charriage, la deformation ă la pârtie inferieure des nappes etani donc plus correctement decrite comme une combinaison entre le cisaillement pur avec un cisaillement simple. En accord avec ce qui a ete ecrit plus haut concernant les traces de la deformation, en base des resultals que nous detenons jusqu’â present, nous considerons que les galets de metaconglomerats analyses constituent les reperes d’un străin plan provoque aussi bien par le poids propre des nappes que par leur propre mouve- ment. En ce qui concerne la relation entre le străin fini et le temps (Ie taux du străin) au cours du processus tectonique etudie. nous considerons comme d’ințeret les observations suivantes. Pour I ești mat ion du taux moyen du străin nous avons recouru â la combinaison des donnees du Tableau 2 avec le temps de 3 Ma (duree du Turonien) necessaire â la generation des deformations etudiees. En appliqua.ul les formules de calcul indiquees par Pfiffner et Ramsay (1982) nous avons etabli que le străin d’extension (ej varie entre 2,07 et 0,24, tandis que le străin de raccourcissement (ea) varie entre 0.04 et -0.30. (’onformement ă ces valeurs, le taux du străin (e) pour extension est compris entre 2,19X10“'''s-1 et 0.25X10”14s-1 et celui pour raccourcissement oscille entre 0,32X10“14s-1 et 0,67X10“J4s“*. Selon Pfiffner et Ramsay (1982) ii est â attendre que des taux plus rapides que 10“13s-1 produisent des contrainl.es de grande intensite tandis que des taux sous 10“l5s-1 vont conduire â des deformations tres reduites (roches aparernment nou deformees). \ laide du diagramme de la Figure 12, en connaissant le taux du străin, on peut deduire graphiquement I imenși te de la deformation â un moment doime de l’histoire geologique. En ce qui concerne nos donnees, el les se simeni entre les courbes du taux du străin de 10“14s-1 et 10“15s-1 et correspondent â des deformations d’intensite reduite ou moderee. Cette observation vient ă confirmer nos resultats anterieurs obtenus toutefois par d autres methodes (Dimitrescu, 1995). Conclusions 1. L’analyse du străin bi-dimensionnel effectuee par la methode Ry/o a mis en evidence la symetrie des distributions initiales des galets. 2. L’analyse tri-dimensionnelle du străin a montre que celui-ci est le produit d’une seule phase do deformation, commune a toutes les nappes de charriage etudiees. 3. Le străin plan conserve par les galets des metaconglomerats s’eloigne en certains points d’observalion de la ligne k=l, en se situant dans le champ de l’extension, ce que nous pouvons interpretei- comme du a la superposition simultanee d’un cisaillement pur dominant sur un cisaillement simple de petite intensite. 4. Le calcul du taux du străin a permis la. determination de l’intensite de la deformation provoquee par le charriage des nappes des Monts Apuseni du Nord au temps du Turonien. Bibliographie Coward. M. P. (1976) Străin within ductile shear zones. Tectonophysics, 34, p. 184-197, Amsterdam. —■ , Kim. J. H. (1981) Străin within thrust shects. In: Thrust and nappe tectonic». Spec. Puhl. geol. .Soc. Landou, 9, p. 275-292, London. Dimitrescu. M. (1995) Variația formei găleților metaconglomeratelor paleozoice din Bihorul de Sud. Stud. cerc. geol.. 40. p. 3-18, București. (1997) Studiul petrologie al metaconglomeratelor paleozoice din Munții Bihor. Teză nepublicată, Univ. București. Dunnet. D. (1969) A technique of finite străin analysis using elliptical particles. Tectonophysics, 7/2, p. 117-136, Amster- dam. . Siddans, A.W.B. (1971) Non random sedimentary fabrics and their modification by străin. Tectonophysks. 12/4, p. 307-325. Amsterdam. Ghosh. Y. K. (1978) Measure of non-cooaxiality. J. Struct. Geo/., 9/1, p. 111-113, Oxford. Hanna, S.. Fry, N. (1979) A comparison of methods of străin determination in rocks from Southwest Dyfed (Pcmbrokeshire). J. Struct. Geol., 1/2. p. 155-162, Oxford. Kligfield, R... Caruiignani. L.. Owens, W. H. (1981) Străin analysis of a Northern Apennine shear zone using deformed marblc breecias. J. Struct. Geol., 3/4, p. 421-436, Oxford. 21 M. DIMITRESCC Lisle. li. .1. (1977) Glastic grain shape and orientation in relation to cleavage from the Aberystwyth Grits, Wales. Tectono- phy»ics, 39. p. 381-395. Amsterdam. (1985) Geological străin analysis. A manual for the Rf/e technique. Pergamon Press, 1-100, London. (1980) The secționai străin cllipse during Progressive cooaxial deformations. J. Struct. Geol., 8/7, p. 809-817, Oxford. Mathews. P. E., Bond. R.. Van den Berg, J. (1974) An algebraic method of străin analysis using elliptical markers. Tecionoph.vsics. 24/1-2, p. 31-67, Amsterdam. Meaus. W. O.. Hobbs. B. E.. Listei-. G. S.. Wiliams. P. F. (1980) Vorticity and non-cooaxiality in Progressive defor- malions. .1. Struct. Geo/.. 2/3. p. 371-378, Oxford. Milton. N. .1. (1980) Determinai ion of the străin ellipsoid from measurements on any three secționa. Tectonophysio. 64. TI9- Î27. Amsterdam. Olarn. L.. Diniitrescu. R. (1994) Contribuții preliminare la cunoașterea vârstei Seriei de Păiușeni din masivul Highiș. Rom. .1. St rut igraphy, 76. p. 1-5. Bucureșt i. Patersou. S.R. (1983) A comparison of methods used in measuring finite străin from ellipsoidal objccts. J. Struct. Geo/., •5/6. p. 61 1-618. Oxford. Peach. C.. Lisle. R. .1. (1979) A FORTRAN IV program for the analysis of tectonic străin using deformed elliptical markers. Comp. TREND 357 PLUNGE ț S LENGHT 1.035 AXIS NUMBER 3 TREND 91 PLUNGE 6 LENGHT 0.927 X:Y:Z = 2.339: 1.116: 1.000 I.ODES PARAMETER = -0.742 ES VALUE = 0.860 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 181 AND DIP 84 2.Valea Negrii SECTION 1 DIP 85 STRIKE 310 PITCH OF ELLIPSE LONG AXIS SECTION ' O DIP 55 STRIKE 150 PITCH OF ELLIPSE LONG AXIS SECTION 3 DIP 65 STRIKE 180 PITCH OF ELLIPSE LONG AXIS 2.4981923 90 81 45 ELLIPSE RATIO 2.160 ELLIPSE RATIO 1.820 ELLIPSE RATIO 2.640 1.2525140 1.2136556 PRODUCT OF ADJUS TMENT FACTORS 0 6173 SECTION 1 ADJUSTMENT ELLIPSE RATIO SECTION 2 ADJUSTMENT ELLIPSE RATIO SECTION 3 ADJUSTMENT ELLIPSE RATIO MATRIX REPRESENTING ELLIPSOID 0.813 0.807 0.809 0.334 -0.786 -0.104 -0.786 -0.023 -0.180 -0.104 -0.180 0.333 3D FIGURE IS NOT AN ELLIPSOID AXIS NUMBER 2 TREND 217 PLUNGE AXIS NUMBER 3 TREND 321 PLUNGE 78 LENGHT 3 LENGHT 1.638 1.019 3. Cascada Vârciorogului SECTION 1 DIP 80 STRIKE 315 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 2.690 SECTION DIP 40 STRIKE 135 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 1.920 SECTION 3 DIP 85 STRIKE s PITCH OF ELLIPSE LONG AXIS 45 ELLIPSE RATIO 2.740 1.4142136 1.5581819 1.0191886 PRODUCT OF ADJUSTMENT FACTORS 0.3212 SECTION 1 ADJUSTMENT ELLIPSE RATIO 0.670 SECTION 2 ADJUSTMENT ELLIPSE RATIO 0.670 SECTION 3 ADJUSTMENT ELLIPSE RATIO 0.674 MATRIX REPRESENTING ELLIPSOID 0.727 -0.327 0.156 -0.327 0.620 0.104 0.156 0.104 0.242 AXIS NUMBER 1 TREND PLUNGE 53 LENGHT 3 119 AXIS NUMBER 2 TREND 54 PLUNGE 37 LENGHT 1.446 AXIS NUMBER 3 TREND 321 PLUNGE 4 LENGHT 0.996 X:Y:Z = 3.131: 1.452: I.000 I.ODES PARAMETER “ -0.347 ES VALUE = 0.938 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 51 AND DIP 86 Institutul Geological României 2(5 M. D1M1TRESCV 4. Pârâul Corbului SECTION 1 DIP 0 STRIKE 270 PITCH OF ELLIPSE SECTION 2 DIP 85 STRIKE 310 PITCH OF ELLIPSE SECTION 3 DIP 85 STRIKE 238 PITCH OF ELLIPSE 1.5557238 1.0058303 1.8870799 LONG AXIS 90 ELLIPSE RATIO 1.840 LONG AXIS 90 ELLIPSE RATIO 1.580 LONG AXIS 45 ELLIPSE RATIO 1.630 PRODUCT OF ADJUSTMENT FACTORS 1.7230 SECTION 1 ADJUSTMENT ELLIPSE RATIO 1.204 SECTION 2 ADJUSTMENT ELLIPSE RATIO 1.202 SECTION 3 ADJUSTMENT ELLIPSE RATIO 1.202 MATRIX REPRESENTING ELLIPSOID 0.266 -0.116 0.217 -0 116 0.826 0.140 0.217 0.140 0.366 AXIS NUMBER 1 TREND 197 PLUNGE 38 LENGHT AXIS NUMBER 2 TREND 351 PLUNGE 49 LENGHT AXIS NUMBER 3 TREND 96 PLUNGE 13 LENGHT X:Y:Z -4.099: 1.276: 1.000 LODES P.ARAMETER = -0.654 ES VALUE = 1.362 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE MAS STRIKE 4.392 1.368 1.072 186 AND DIP 77 5. Valea Plaiului SECTION 1 DIP 85 STRIKE 270 PITCH OF ELLIPSE SECTION 2 DIP 15 STRIKE 45 PITCH OF ELLIPSE SECTION 3 DIP 85 STRIKE 225 PITCH OF ELLIPSE 62.3909494 1.4142136 1.0044738 LONG AXIS LONG AXIS LONG AXIS 90 ELLIPSE RATIO 90 ELLIPSE RATIO 45 ELLIPSE RATIO 2.150 1.690 1.270 PRODUCT OF ADJUSTMENT FACTORS 0.3848 SECTION 1 ADJUSTMENT ELL1PSE RATIO 0.698 SECTION 2 ADJUSTMENT ELLIPSE RATIO 0.707 SECTION 3 ADJUSTMENT ELLIPSE RATIO 0.698 MATRIX REPRESENTING ELLIPSOID 0 558 0.109 0.274 0.109 1.008 -0.051 0.274 -0 051 0.389 AXIS NUMBER I TREND AXIS NUMBER 2 TREND AXIS NUMBER 3 TREND X:Y:Z = 2.445: 1.175: 1.000 168 PLUNGE 52 LENGHT 345 PLUNGE 38 LENGHT 76 PLUNGE 1 LENGHT LODES PARAMETER = -0.640 2.405 1.156 0.984 ES VALUE = 0.856 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 166 AND DIP 89 6. Piatra Molivișului SECTION 1 DIP 85 STRIKE 310 PITCH OF ELLIPSE LONG AXIS 45 ELLIPSE RATIO 2.270 SECTION 2 DIP STRIKE 130 PITCH OF ELLIPSE LONG AXIS 88 ELLIPSE RATIO 2.520 SECTION 3 DIP 85 STRIKE 215 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 1.910 ! 5557238 2.3683052 1.0083502 PRODUCT OF ADJUSTMENT FACTORS 4.1415 SECTION 1 ADJUSTMENT ELLIPSE RATIO 1.620 SECTION 2 ADJUSTMENT ELLIPSE RATIO 1.619 SECTION 3 ADJUSTMENT ELLIPSE RATIO 1.636 MATRIX REPRESENTING ELLIPSOID 0.275 -0.102 -0.101 -0.102 0 653 0.250 -0.101 0.250 0.232 AXIS NUMBER 1 TREND 313 PLUNGE 62 LENGHT 3.164 AXIS NUMBER n TREND 201 PLUNGE 11 LENGHT 1.975 AXIS NUMBER 1 TREND 106 PLUNGE LENGHT 1.115 X:Y:Z = 2.836: 1.771: 1.000 LODES PARAMETER - 0.096 ES VALUE = 0.717 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 196 AND D:P 65 Institutul Geologic al României I WAI.YSE Dl' S77M/.V ET ȘES IMPUCATIONS 1. Valea Bucegița SECTION 1 DIP 85 STRIKE 318 PITCH OF ELLIPSE LONG AXIS 45 ELLIPSE RATIO 2.170 SECTION 2 DIP 50 STRIKE 70 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 2.680 SECTION 3 DIP 85 STRIKE 208 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 2.710 1.3754652 1.6832539 1.0115661 PRODUCT OF ADJUSTMENT FACTORS 10499 SECTION SECTION SECTION ADJUSTMENT ELLIPSE ADJUSTMENT ELLIPSE ADJUSTMENT ELLIPSE RATIO RATIO RATIO 1.020 1.020 1.020 2 MATRIX REPRESENTING ELLIPSOID -0.019 0.436 0.508 1.736 3.732 0.436 1.216 1.736 -0019 AXIS NUMBER 1 TREND 329 PLUNGE 36 LENGHT 2.385 AXIS NUMBER 2 TREND 160 PLUNGE 54 LENGHT 1.263 AXIS NUMBER 3 TREND 63 PLUNGE 5 LENGHT 0.464 1.000 LODES PARAMETER - 0.224 X:Y:Z = 5.144; 2.724: ES VALUE = 1.099 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 153 ANDDIP 8. Cetatea Siria SECTION 1 DIP 85 STRIKE 310 PITCH OF ELLIPSE SECTION 2 DIP 35 STRIKE 90 PITCH OF ELLIPSE SECTION 2.5334266 2.2202984 1.0056874 3 DIP 85 STRIKE 240 PITCH OF ELLIPSE PRODUCT OF ADJUSTMENT FACTORS 1.1944 SECTION I ADJUSTMENT ELLIPSE RATIO 1.064 SECTION 2 ADJUSTMENT ELLIPSE RATIO 1 064 SECTION 3 ADJUSTMENT ELLIPSE FGXTIO 1.064 MATRIX REPRESENTING ELLIPSOID LONG AXIS 45 ELLIPSE RATIO 1.620 LONG AXIS 88 ELLIPSE RATIO 1.720 LONG AXIS 90 ELLIPSE RATIO 1.630 0 173 0.243 -0.186 0.243 1.484 0.17! -0.186 0.171 0.622 AXIS NUMBER 1 TREND 348 PLUNGE 21 LENGHT AXIS NUMBER 2 TREND 192 PLUNGE 67 LENGHT AXIS NUMBER 3 TREND 81 PLUNGE 9 LENGHT X:Y:Z = 5.669: 1.5 06: 1.000 LODES PARAMETER = -0.528 ESVALUE= 1.567 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE 4 556 1.210 0 804 171 ANDDIP 81 9. Valea Sălăndaș SECTION 1 DIP 5 STRIKE 275 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 1.760 SECTION 2 DIP 85 STRIKE 300 PITCH OF ELLIPSE LONG AXIS 45 ELLIPSE RATIO 1.930 SECTION 3 DIP 85 STRIKE 230 PITCH OF ELLIPSE LONG AXIS 90 ELLIPSE RATIO 1.880 26 8769401 1.0056874 16.1083541 PRODUCT OF .ADJUSTMENT FACTORS 0.4598 SECTION I ADJUSTMENT ELLIPSE RATIO 0.773 SECTION 2 ADJUSTMENT ELLIPSE RATIO 0.772 SECTION 3 ADJUSTMENT ELLIPSE RATIO 0.772 MATRIX REPRESENTING ELLIPSOID 0.492 0.149 -0.270 0.149 1.219 0.285 -0.270 0.285 0.573 AXIS NUMBER 1 TREND 338 PLUNGE 42 LENGHT 2.411 AXIS NUMBER 2 TREND 195 PLUNGE 42 LENGHT 1.131 AXIS NUMBER 3 TREND 86 PLUNGE 19 LENGHT 0.867 X:Y:Z = 2.779: L. 304: 1.000 LODES PARAMETER = -0.481 ES VALUE - 0.901 TECTONIC CLEAVAGE AS DEFINED BY X:Y PLANE HAS STRIKE I 76 AND D1P 71 Institutul Geological României Institutul Geological României An. Inst. Geol. Rom., 72, part. II. p. 29-35, București, 2000 wAr -39Ar LASER PROBE DATING ON SINGLE CRYSTALS FROM TRONDHJEMITIC DIKES - SEBEȘ-CIBIN MOUNTAINS (SOUTH CARPATHIANS) - ROMANIA Anca DOBRESCU1, Patrick SMITH2 1 Geological Institute of Romania, 1 Caransebeș St., RO-79678 Bucharest 32, Romania 2 Depart. of Physics, University of Toronto, Toronto, Ontario M5S 1A7. Canada Key words: Trondhjemites. 40 Ar/39 Ar method of dating. Getic-Supragetic Do- mains. South Carpathians. Abstract: Single biotite, plagioclase and quartz crystals from porphyritic trond- hjemites have been analyzed for 40 Ar/39 Ar isotopes. The dike System occurs along and within a shearing belt. of almost 90/2 km in the north Sebes-Cibin Mts. (South Carpathians), which separates the Getic and the so-called Supragetic Reahn. Struc- turally, the trondhjemitic dikes are variably deformed to undeformed, suggesting either a heterochroneous emplacement or a differential response to the brittle shearing as- sociated with the Alpine metamorphic event. LASER step-heating 40 Ar/39 Ar age determinations on three different minerais (biotite, plagioclase and quartz) are dis- cussed here. A plateau age of 108.4+0.5 Ma from biotite from an undeformed rock is identical to its integrated age, indicating negligible Ar loss since rapid cooling of the mineral through its closure temperature. Another biotite from a different trond- hjemitic dike shows small amounts of Ar loss in low temperature gas fractions. Its plateau age of 109.3+0.5 Ma is almost concordant to that one from the previous dated rock. Consequently, the 40 Ar/39 Ar data on biotites show the igneous cooling age of the trondhjemitic magma from two different dikes, meaning that this age represents the coeval intrusion of these bodies, responding differently to the brittle shearing stage, probably related to the Austrian phase. Most of the plagioclase phenocrysls are slightly altered and their age-spectra are problematic, indicating both excess Ar and younger ages relative to biotite. These effects may be attributed to an event at 96 - 95 Ma. Similar ages appear to be registered by inclusions within quartz crystals. The coincidence b<^ween the Albian-Aptian age of t.he trondhjemitic dikes and the supposed age of the overthrust precludes the idea of the overthrust position of the Getic - Supragetic Domains, at least on the outcropping area of the swarm of dikes. Considering the main geochemical characteristics of the low-K magmatism related to some tectonic and geochronological data, the genesis of these dikes could be related to the subduction of an oceanic crust of Severin Nappe type beneath the Getic Domain. Introduction The scarcity of geochronological data in the South Carpathians, but moreover the significance of a low-K granitoidic (trondhjemitic) magmatism along an important shearing zone, was a stimulating motif to perform the 40 Ar/39 Ar incremental heating method of dating on individual crystals from trondhjemitic dykes. Dating K-bearing minerais (biotite, plagioclase and quartz(!)) from deformed to undeformed rocks, we demonstrate the feasibility of using 40 Ar/39 Ar single-crystal LASER-probe method to separate the effects of deformation induced by a tectonic event, from the cooling age of the trondhjemitic dikes. Geological setting and geochemical constrains The shearing zone (90Km/2 km) (Fig. 1) along and within which the swarm of over 300 trondhjemitic dikes occurs. has a quite controversial significance in the tectonic models of the northern South Carpathians: Institutul Geological României A. DOBRESCU. P. SM1TH 30 Fig. 1 - Sketch-map of the northern part of the Sebeș-Cibin Mts. A - reverse fault. (Chivu, 1968; Savu, 1978) cross-cutting the Sibișel series; B - thrust fault (Balintoni et al, 1989), separating the Getic Domain from the overlying Supragelic Domain (or even conversely the Getic Domain thrust over the Supragetic Domain (lancu & Mărunțiu, 1994). The shortening event is considered either Austrian (quite contemporaneous to the main tectogenesis alfeeting the Central Ea.st and South Carpathians Nappes (Săndulescu, 1984) in the first hypothesis, or Pre-Alpine (related to the M2 dynamo-thermal metamorphic event) in the second oue; C - strike-slip fault (Stelea, 1994) (at least on the SW-NE segment) initiated probably in Lower Jurassic. I’he trondhjemitic dikes (Dobrescu & Stoian, 1994, Dobrescu, 1995) have been characterized as belonging io a CA low-K (alinost exclusively trondhjemitic) magmatism. The main geochemical features are: low Rb, Ba, Zr abundance, moderate Sr contents; low REE contents, low Yb values, moderate to high (La/Yb)n ratios and increasing Sr/Y with decreasing Y (indicating a parțial melting process of metabasaltic rocks - Drummond & Defant. 1990); low 87Sr/86Sr (0.702 - 0.704) (typical of mantie derived magmas or of crustal- derived magmas with a metabasic source); These geochemical features both with several other considerations (see the above mentioned papers) could be explaiued by deep-seated dehydration parțial melting of a metabasic source. This could be appropriate for convergent, margin setting (confirmed by plots on Pearce’s et al., 1984 diagrams - in Dobrescu, 1998) where convergence-related imbrication places mafie terranes in deep crustal environments. Analytical technique We present here an example of 40 Ar/39 Ar age spectra for biotite, plagioclase and quartz crystals derived by LASER step-heating on individual grains. It. was used the LASER fusion system at the University of 40Ar -39Ar LASER PROBE DATING ON SINGLE CRYSTALS FROM TRONDHJEMITIC DIKES 31 Toronto which consists of a Spectra-Physics 171-18 (18 Watt) continuous argon-ion laser and a VG 1200S mass spectrometer with a Baur-Signer ion source and an electron multiplier. For comparison it was used a hornblende Hb3gr spectrum standard (Zartman, 1964 in Layer et al., 1987), a widely used Precambriau standard with an assumed age of 1071 m.y. Sample description This study presents analytical data from LASER, incremental-heating experiments on 6 single grain .samples. The crystals (biotite, plagioclase and quartz phenocrysts) were separated from three porphyritic t.rondhjemitic bodies, situated in different places vs. the shearing zone. Sample St9c The biotite. plagioclase and quart.z grain samples belong to the most basic t.rondhjemitic sili which was mapped in the area (SiO2 = 62.95 %). The sili lies concordant between low metamorphic crystalline schists and crystalline limestones, downstream Cetățelei Brook, in the central part of the area. It has a "high- porphyritic” (large and dense phenocrysts), almost undeformed structure. Plagioclase, quartz. biotite and random altered hornblende phenocrysts are widespread in a microcrystalline matrix. The sample, taken from the core of the sili, exhibits very well defined, sometimes zoned or twinned plagioclase (Ams-Anog) laths, slightly sericized inainly in the iniddle of the phenocrysts. The fine biotite crystals are slightly chloritized, but the bigger ones (0.8 mm in length), which were used in our experiments, are mostly unaltered. The quartz phenocrysts, which sometimes are paramorphs of /Tquartz on o-quartz, are rather undeformed. Sample S80 The dike occurs on the Sebeș valley, near Căpâlna. It is high-silicic (73.61 %), high-porphyritic, with coarser crystallized matrix than sample S79c and fairly undeformed. Large plagioclase phenocrysts are sometimes twinned, rarely zoned. Biotites are long-shaped, a little more altered than the biotites in sample S79c. Sample 6182 The sample was taken from a trondhjemitic dike from the Râușoru valley, western part, of the area. It is a remarkable fresh rock, ”low-medium porphyritic” with a. fine microcrystalline matrix and a slightly oriented structure with aligned and sometimes long kink-waved biotite crystals. The quartz (sometimes dipyramidal) and plagioclase phenocrysts have waved extinction and sometimes biotite inclusions. Results The Ar-Ar data for step-heating analyses of 6 mineral crystals are summarized in Table 1. Significant gas fractions from the biotite sample S79c give concordant ages, resulting in a plateau age of 108.4+0.5 Ma that is identical to the integrated age of 108.1+0.5 Ma (Fig. 2A). The undisturbed age spectrum for this sample indicates negligible Ar loss since rapid cooling of the mineral through its closure temperature. The age-spectrum for S80 biotite from another trondhjemitic dike shows small amounts (less than 20 %) of Ar loss in low temperature gas fractions. However, age plateau at 109.3+0.5 Ma for the remaining gas fractions is indistinguishable from the age of sample S79c. Thus, the ages of biotite from both dikes are the same within uncertainties. The age spectra for the plagioclase crystals are more complex compared to their associated biotite. There are also geochemical differences between the feldspars indicated by a Ca/K of 18.3 for S80, which is significantly higher than the ratio of 5.8 for S79c. The spectrum of plagioclase S80 shows the effects of excess Ar in the low-temperature fractions 1-4, which is reflected in its high integrated age of 124.4+2.0 Ma. These effects can be circumvented by the use of an isotope correlation plot of 39 Ar/40 Ar vs. 36Ar/40Ar. On this plot, fractions 7-12 are co-linear within experimental uncertainties and yield an age of 111.3+4.5 Ma. This isochron age is within the uncertainties of the biotite age of 108 Ma. Plagioclase from samples S79 gives an integrated age of 96.2+0.8, significantly younger than that of S80. An isochron fit through points 4 to 11 gives an indistinguishable estimate of 96.5+2.3 Ma (Fig. 2C). Institutul Geological României .4. DOBRESCU, P. SMITH Institutul Geologic al României «'Ar Air LASER PROBE DATING ON SINGLE CRYSTALS FROM TRONDHJEMITIC DIKES 33 Integrated < < s79c 0.01 ±0.01 3.1810.02 0.35±0.02 O 03 CD 0.067 10.004 9.9810.05 6182 o d +i co d voljaAr 10'12 23.6 13.7 20.8 4.9 4.4 Age 108.110.5 96.210.8 106.1±0.6 124.4±2.0 103.7+1.7 Isochron fc-u) ZSwnS 0.75 1.52 Inițial 385196 484±85 Age co ■H CO O T— 95±3 Plateau ox <0 r* CD CO V- O CO o z CD t- r- co Age 108.410.5 -9617 9’L+1/914 90+960L c ” eum (Neumayr) Holcopbylloccras potyclcum (Beixxike) Progeronia progeron (Ammon) Ortbosphinctes sp. aff. O. selectul (Neumayr) Taramelliceras (Metahaploceras) slrombeckJ (Oppel) Physcdoceras wlfi (Neumayr) Physodooeras altenense (Oppel) Lytocriras pdycyclum Neumayr Phyllocera» Isotypurn (Canavari) Lesslr»ceras ptychodes (Neumayr) Ataxioceras cf. metamorphus (Neumayr) Progeronia cf triplez (Quenctodt) Progeronia cf pseudolldor (Choffal) Crussoliceras dMsum (Ouenstedt) Prcsimocera» fuclnii (Canavari) Taramelliceras (T.) trachlnotum (Oppel) Crussoliceras tenulcostatum Geycr Crussoliceras geyeri Otora Garnierisphinctes cf. champlonneU (Fontannes) St/eblitos cf. Scviplctus (Fontannes) Strebiites tenuilobatus (Oppel) Glochiceras crenosum (Quenstedt) Sowerbyceras lon/l morpha loryi (Munler Chalmas) Pseudosimoceras sp. Taramelliceras (T ) pseudoflexuosum (Favre) Nefcrodltes agrigentinus agrigentinus (Gemmellaro) Asprdoceras ar.antNcum {Oppel m Neumayr) Taramelliceras (T.) compsum compsum (Oppel) Orthaspldocatras uNandi (Oppel) Presimoceras cf. herbicht (Hauer in Neumayr) Presimoceras cf. planulaclnctum (Quenstedt) Presrmoceras sp aff P ludovicii (Meneghml) Nebrodites p«Sto 0.05 0.06 0.07 0.05 0.06 0.10 0.08 0.14 0.17 0.10 0 site 4.00 4.00 4.00 4.00 4.00 #Mn +“ 3.85 3.69 3.34 4.03 3.92 #Mg+' 0.01 0.02 0.02 0.01 0.01 #Ca+“ 2.14 2.27 2.60 1.96 2.07 A site 6.00 5.98 5.95 6.00 6.00 Genesis At least two mineral assemblages can be distinguished in the piemontite porphyroids: an older one. con- taininggarnet+quartz+K-feldspar+plagioclase, and ayounger one, with piemontite+clinozoisit.e+phengite+ albite+quartz. The former resulted from the interaction between the Cambrian rhyolites of Tg3 Formation and the protoliths of the nowadays black quartzites of Tg2 Formation, containing a minor Mn mineral- ization. The Mn-Ca carbonates reacted with the acidic rocks to form Mn-Ca garnets. Subsequently, the garnet-bearing porphyroids have been affected by extended shearings that belong to the Valea Seacă fault system. Faulting-related mylonitization enabled circulation of oxidizing Solutions. The oxidation of Mn2+ to Mn3+ instabilized the garnets that dissoluted in order to form piemontite. Concurrently, the plagioclase and K-feldspar were replaced by an almost pure albite. The released Ca participated to the formation of t he epidote minerals and the potassium has been fixed in phengite. Noteworthy, many porphyric albite crystals have phengite rims. The composite crystals, with piemontite cores and clinozoisite rims are the result of changes in fluid composition. The early fluids leached the Mn from the crushed garnets and enabled the piemontiteformation. The later fluids had less Mn to leach, their composition became Mn-poorer and they formed clinozoisite Institutul Geological României 58 M. MUNTEANU instead of piemontite. The essential role of the fluids in the formation of the epidote minerals is proved by ihe (act that in the less mylonitized zones, where the garnets preserved uncrushed, the piemontite formed only as veins along cracks. Conclusions The piemontite porphyroids from Valea Seacă preserved a metasomatic assemblage, partly altered due to oxidizing fluids that circulated along faults. This paper reports for the first time gârneț and piemontite in the East Carpathian porphyroids. References Brown, W. L., Parsons, I. (1981) Towards a more pratical two feldspar geothermometer. Contributions to Mineralogy and Petrology, 76, p, 369-377. Catti. M., Ferraris, G.. Waldi, G. (1989) On the crystai chemistry of strontian piemontite with some remarks n the noinenclature of the epidote group. Nenea Jahrbuch fur Mineralogie Monatshefte, p. 357-366. Green. N. L., Usdansky, S. I. (1986) Toward a practicai plagioclase-muscovite geothermometer American Mineralogist, 71, p. 1109-1117. Massonne, H. J.. Schreyer, W. (1987) Phengite geobarometry based on the limiting assemblage with K-feldspar. phlogo- pite and quartz. Contributions to Mineralogy and Petrology, 96, p. 212-224. Roșu. E.. Vodă. A., Costea. C., Niță, P. (1998) Sphalerite geobarometry and arsenopyrite geothermometry applied to some inetamorphosed sulfide ores of the Tulgheș Group, East Carpathians, Romania. Carpathian-Balkan Geological Association, XVI Congress, Vienna Abstracta Volume, p. 525. Vodă. A. (1999) Contribuții la cunoașterea structurii geologice a zonei cristalino-mezozoice a Carpaților Orientali, sectorul central. Stud. cerc, geol., in press. (GR. Institutul Geological României An. Inst. Geol. Rom.. 72, part. II. p. 59-66, București, 2000 SOME ASPECTS REGARDING MORPHOLOGICAL VARIATIONS OF ZIRCON CRYSTALS FROM MUNTELE MIC MASSIF, SOUTH CARPATHIANS-ROMANIA: PETROGENETIC IMPLICATIONS Ion Niculae ROBU, Lucia ROBU Geologica) Institute of Romania. 1 Caransebeș St.. RO-79678 Bucharest 32 Key words: Zircon. Morphology. Pyramid and prism faces. Granitoid. growth, typology. Abstract: Muntele Mic is considered to belong to Caledonian granitoids of the South- ern Carpathians. It is intruded in the Precambrian medium-grade crystalline forma- tions of the Zeicani, Godenele, Măgura-Marga and Barnita Series, from the Upper Danubian Units. It is composed of granitoid rocks, as granites, granodiorites and, sometimes diorites. A specific characteristic of the massif is the small quautitv of mafie minerals, as hornblende or/and biotite, the majority of the identified petrotypes being leucrocrate ones. As an exception. diorites must be mentioned. with a stronger mafie character due to a high proportion of biotite. Zircon crystals, identified using a specific methodology for heavy minerals, are usually associated with common ac- cessory minerals of the granitoid rocks, as apatite, gârneț, magnetite. Zircons are characterized by a long prismatic habit, determined by the large developmenl of the prism faces. There is an obvious predominance of the (110) prism faces comparativei'' with the (100) ones. The pyramid (101) faces are much better developed, then the (211) ones. These growth differences determined two morphological types: • simple crystals, with simple terminations, determined by well-development of (110) and/or (110) prism faces associated with (211) pyramid one: • complicated crystals. with complicated terminations, that have well-developed (110) and/or (100) prism ones combined with (201) and (101) pyramid ones. The typological study (according to Pupin, 1980) has emphasized morphological types, crystallized from melts wit h deep source, pointing out the possibility for some crustal contamination. Sometimes zircon crystals are overgrown, zoned and contain opaque and/or transparent, (zircon, apatite) minerals. Introtl uction Previous studies (Codarcea et al., 1963; Gherasi, Savu, 1969; Savu et al., 1973; Krăutner et al.. 1981: Berza et al., 1983, 1993) in the Muntele Mic area. have included some considerations regarding petrography, mineralogy and geochemistry of this massif, without presenting some information about accessory minerals. especially about their morphological aspects and their implications in the petrogenetic interpretat ions. This paper tries to emphasize the morphology and the optica! properties of zircon crystals enclosed in granitic rocks of the Muntele Mic massif, to establish the existing connections between morphological characteristics of zircons and physico-chemical conditions of their crysta.llizat.ion environment, and to present. how could these ones be used in petrogenetical interpretations. Geological setting The actual geological data (Gherasi, Savu, 1969; Savu et al., 1973) include Muntele Mic granitoid body and its country rocks, Precambrian polymetamorphic crystalline formations of the Zeicani, Godenele, Măgura-Marga, Maru and Barnita Series (Fig. 1) of the Upper Danubian Units (Berza et al., 1983, 1993). Institutul Geological României (50 I. N. ROBU, L. ROBI. Hg. 1 Geologica! map of the Muntele Mic granitoid massif. Institutul Geological României M0RPH0L0G1CAL VARIAT10NS OF ZIRCON CRYSTALS 61 Fig. 2 - Main types and subtypes of typologic classification of zircon crystals (Pupin, 1980). Its shape is an ellipsoid, NNE-SSW oriented, according to its long axes, parallel to an antiform structure, that included it. It is divided in two different parts, a northern uplifted part and a Southern down-thrown. by the Vârciorova-Craiul fault (Gherasi, Savu, 1969). Muntele Mic granitoid massif is surrounded by crystalline formations, grouped in some different meta- morphic series, and by Mesozoic sedimentary deposits, as follows: • Măgura-Marga Series, composed of quartz-biotite-chlorite schists and chlorite-albite-sericite schists and Barnita Series, enclosing metamorphosed basic schists, met in the Eastern part of the massif; • Marti Series, constituted of amphibolites, metaquartzdiorites, metagabbros and sometimes metaultra- mafites, cropping out to the West of the massif; o Mesozoic sedimentary formations, cropping in the Southern and South-Eastern parts of this one. Petrography and minei-alogy Muntele Mic granitoid massif is characterized by petrographical and mineralogica! homogeneity in its entire area. 62 I. N. ROBU, L. ROBU Granodiorites and granites are the main petrographical types, but sometimes diorite or quartz diorites can be observed, especially in the northern part of the massif, where a narrow zone (6-7 km long and 1 km apparently thick) has been separated, having the same orientation as the long axes of the body (Gherasi, Savu. 1969). The porphyric structure and an oriented fabric are specific for all petrotypes, but they are difficult to organize in the Southern part of the massif, along the Vârciorova-Craiu fault and in the Bistra Mărului Basin, where the granitoid rocks present mylonitic aspects. Feldspar, micas and quartz have been observed as main mineralogical phases: • Feldspar (plagioclase and/or alkaline-microcline-perthite) has been observed (1) in the matrix of the rocks and (2) as well-developed crystals, that determined the porphyric character of the structure. Frequently it is partially or totally substituted by albite. o Micas are represented by biotite, that includes zircons, or is intergrown with muscovite. Sometimes muscovite can be observed as main micas phases. • Quartz is present as anhedral crystals. associated to feldspar and micas, constituting the last mineral phase. Frequently it is broken or presents wavy aspects. As accessory minerals we have identified: zircon, apatite, titanite, magnetite. Mineral species and mineral associations are presented in table 1. Table 1. Accessory minerals in investigated rocks from Muntele Mic granitoid massif Primary minerals Secondary minerals Sample Petrotype Zircon Apatite Titanite Magnetite Pyrite Epidote 5091 granițe + - - 4- 4- - 5106 granițe + + - 4- 4- - 5107 granițe + - 4- 4- 4- 4- 5108 granițe + + - 4- 4- - 5110 granițe + + - 4- 4- - 5118 granițe + + 4- 4- - 5119 granițe + 4- - 4- 4- 4- 5109 microgranite + + - 4- 4- 4- 5096 granodiorite + + 4- 4- 4- - 5094 granodiorite + 4- - 4- 4- - 509.5 diorite + - - 4- 4- 4- 5093 diorite + 4- - 4- 4- - + = ycs; - = no Chemistry Chemical characterization of the granitic rocks from Muntele Mic massif (content, variation and inter- pretation) (Savu et al., 1973) is emphasized, as follows: • Main elements - SiO2 content varies between 68.54 % and 53.24 %, determining for all investigated petrotypes an acid-intermediary character; - alkaline elements have relatively high values, varying between 5.10 and 3.38 % for Na2O, and 1.43 and 4.37 %, for I<20, and their sum (S K2O+Na2O) is between 5.08 and 8.89 %. The Na-character (K2O5-10% >10-20% i f h >20-30% S >30% F'ig. 3 - Tipologic distribution of zircon populations from Muntele Mic granitoid inassif (Pupin, 1980). 64 L N. ROBU, L. ROBU UREE concentration. A petrogenetic interpretation, based on REE content and variation, envolves complex geological aspects as (1) a deep magma generation and (2) crustal assimilation processes. Physical aspects of zircon crystals Physical properties, important for zircon characterization and used in petrogenetical interpretations, are t he colour and optica! aspects (crystal inside). Colour is variable in the zircon studied populations, without significant differences between zircons from the investigated petrotypes. These ones are determined by the number of different coloured crystals, in the same population, the majority of zircon crystals are light-dark brown and a few are light pink. In spițe of these colour variations, morphological aspects are frequently the same and no connection between colour variations and morphological aspects could be established. The metamictic process, determined by the accumulation and disintegration of the radioactive elements (Th, U-Pb isotopes) enclosed in crystal network of the zircon crystals. affected most of the zircons. Crystars inside is not simple and in many cases is characterized by nucleus, zoning and inclusions. Nucleus is generally disposed in the central part of the crystals, overgrowth developed arround it, be- ing syminetric or asymmetric (plate 1). This itucleus is represented by smaller idiomorphic zircon crystal, sometimes parțial or total rounded ones, having the same optica! orientation with the host zircon crystal. Zoning has a small development, as number of zoned crystals or observed zones in the crystals. The way of zoning is very different, varying from crystal to crystal (plate 11). Generally, zones have an unequal development, in the same crystals or in different crystals, varying from thin to thick; they are observable especially in prism grown area and disposed parallel with prism faces or sometimes pyramid ones. Inclusions, observable in a large number of crystals, are very minute, disposed chaotically, or oriented parallel to prism faces, with different morphological aspects: needles, batons and prismatic aspects (plate 111). The extremely minute dimensions have made difficult their identification by optical method, but their morphological aspects seem to be similar with apatite (long batons) or zircon (prismatic forms); the needle ones could’not be identified. Zircon morphology Some morphological differences have been observed, determined by unequal development of two main faces of zircon crystals: prism and pyramid. Two different aspects could be identified (plate IV). • unequal developed prism faces, when (HO) prism faces are much better developed than (100) [(110) > (100)], due to some Chemical change of the crystallization enviromnenl and temperature variation (Pupin, 1980): high Al-content and low temperature. • unequal developed pyramid faces, [(211) < (101)], determined by K-content increase of the zircon crystallization medium and decrease of the temperature. These variations have as a result the appearance of two different crystal type (plate V): • simple crystals, with simple ending, determined by well developed (110) and/or (100) prism faces, associated with (211) pyramid ones; • complex crystals, with complicated ending, that have well-developed (110) and/or (100) prism ones, combined with (211) and (101) pyramid ones; Typological interpretation (Pupin, 1980) (fig. 2) emhasizes the predominance of L2-5, S3_5, Pi_3 G types, a few P5 type and 811-13, Sig-is and D types have sporadically been observed. No specific forms for each petrotype have been identified, but high percentage variations of these ones have been emphasized (Fig. 3). Their tendency vectors (fig. 3) emphasize a calc-alkaline evolution and their mean calculated points plot in granodiorite, monzogranite and monzonite areas (fig. 4). Institutul Geological României M0RPH0L0G1CAL VARIATIONS OF ZIRCON CRYSTALS 65 -------------------- I.A 100 200 300 IM 500 600 700 800 , 1 I 1 I ■ < . > 100 - 200 - 300 - 400- 500 - 600 ‘ 700 ■ 800 ■ Fig. 4 - Distribution of plutonic rocks in the typologic diagram. (1) diorit.es, quartz gabbros and diorit.es, tonalites; (2) granodiorites; (3) inonzogranit.es and monzonit.es: (4) alkaline and hyperalkaline syenit.es and granites (Pupin 1980). Fig. 5 - Distribution of mean points and mean T.E.T. of zircon population from granitic rocks (1) granites of crustal origin; (2) granites of crustal+mantle origin (hybrid granites); (34-4) granites of mantie or mainly mantie origin (Pupin, 1980). Distribution of mean points in T.E.T. diagram (fig. 5) shows a crystallization process of a granitic composition melt and mix origin (crust+mantle) for this one. Conclusions Some interesting data have resulted from the zircon morphological study of the Muntele Mic granitoids, as follows: • unequal development. of the prism and pyramid faces; Institutul Geologic al României (56 I. N. ROBU, L. ROBU • for each petrographical type, the same zircon morphological types, but different zircon subtypes and different frequency; « two different zircon crystal types: - simple crystals, with simple ending, resulting from well developed (110) and/or (100) prism faces, associated with (211) pyramid ones; - complicated crystals, with complicated ending, having well-developed (110) and/or (100) prism ones, associated to (211) and (101) pyramid ones; • morphological variations, determined by Chemical and temperature exchanges; • a mix origin of the inițial magma emphasized by the typological classification; • a common origin for all investigated petrotypes; « some interesting optical aspect: a variation of colour, from light pink (a few) to light-dark brown (majority) - zoning, especially in the zones of the prism development; core, at the middle of crystals (frequently), or near the margins of crystals (sometimes); - inclusions (needles, batons and minute prisms), disposed in prism zone. References Berza T.. Krăutner, H., Dimitrescu R. (1983) Nappe structure in the Danubian of the centra! South Carpathians. Asoc. Geol. Carp.-Balk., Congr. XII, 1981, București. — . Dimitrescu M., Seghedi, A., Oaie, Gh. (1993) Harta geologică 1: 50.000, foaia Petreanu, Machetă. Codarcea, Al., Pavelescu, L. (1963) Considerations sur la genese des roches granitoides del’autochtone danubien des Carpathes Meridionales. Asoc. Geol. Carp.-Balk., Congr. V, 1961, București. Gherasi, N., Savu, H. (1969) Structura masivului granitoid de la Muntele Mic (Banatul de Est). D.S., LIV/3, București. Krăutner, H., Năstăseanu, S., Berza, T., Stănoiu, I., lancu, V. (1981) Metamorphosed Paleozoic in the South Carpathi- ans and its Relations with the Pre-Paleozoic Basement. Asoc. Geol. Carp.-Balk., Congr. XII, 1981, Guide to Excursion Al, București. Pupin. J. P. (1980) Zircon and granițe petrology. Contrib. Mineral. Petrol., 73, p. 207-220. Robu, I. N., Robu, L., Tiepac, I., Stoian, M., Alexe V. (1997) Raport, Arh. IGR, București. Savu. H.. Vasiliu, C., Udrescu, C., Tiepac, I. (1973) Crystalline schists and Baikalian granitoid rocks in the Muntele Mic region. An. Inst. Geol., XLII, p. 395-44, București. Institutul Geological României I. N. Robu, L. Robu Morphological Variations of Zircon Crystals Plate I — Cores in zircon crystals ® nucleus X1200 Institutul Geological României 1. N. Robu. L. Robu Morphological Variations of Zircon Crystals • Plate II — Zircon crystals, different zoned • zoning x400 x 1200 Institutul Geological României 1. N. Robu, L. Robi: Morphological Variations of Zircon Crystals Plate III — Inclusions in zircon crystals • inclusions Institutul Geologic al României 1. N. Robu. L. Robu Morphological \ariations of Zircon Crystals Plate IV — Variation of growth way of zircon crystals: a. ® unequal developed prism faces [(100) < (110)] b. ® unequal developed pyramid faces [(211) < (101)] x 1200 Institutul Geological României 1. N. Robu. L. Robu Morphological Variations of Zircon Crystals Plate V — Zircon crystal types © two different crystal types: -> simple crystals, with simple ending, determined by well developed of (110) and/or (100) prism faces, associated with (211) pyramid ones; X1200 —5 complicated crystals, with complicated ending, that have well-developed (110) and/or (100) prism ones, combined with (201) and (101) pyramid ones Institutul Geological României An. Inst. Geol. Rom.. 72, part. II, p. 67-76. București. 2000 THE ENCLAVES IN THE EAST CARPATHIAN NEOGENE INTRUSIONS (ROMANIA); THEIR SIGNIFICANCE FOR THE GENESIS OF THE CALC-ALKALINE MAGMAS* Eugenia NIȚOI. Marian MUNTEANU. Ștefan MAR1NCEA Geological Institute of Romania. 1 Caransebeș St., RO-79678 Bucharest 32 Key words: Calc-alkaline magma. Enclaves. Andesites. Intrusive bodies. Abstract: The subvolcanic bodies in the Rodna and Bârgău Mountains contain mag- matic metamorphic and sedimentary enclaves. The study of the enclaves was used to get information about magma evolution. Several pairs host rock-cognate enclaves have been investigated. On the basis of the petrographic, mineralogica! and geochemical features observed, the following condusions can be drawn: (1) the inițial magma was a calc-alkaline one, aciclic or intermediary, with normative corundum. This one could be derived from a basalt-andesitic hydrated magma with normative diopside, as a result of a fractioned-crystallization process; (2) the magma has formed in interme- diary crustal magma chambers at depths of about. 15-20 km. where the estimaied temperature has been 700-800°C and the pressure 6.43-6.83 kbar. The pressure was calculated on the basis of the Chemical composition of hornblende. Pressure values were obtained for both host rocks and enclaves; (3) the cognate enclaves have been considered as evidence for crystallization from a melt initially more mafie (han the one the host rocks have resulted from. Introduction In the northern extremity of the inner part of the East Carpathians, calc-alkaline intrusive bodies were emplaced in Pannonian-Pontian time spân (8.5 Ma-11.7 Ma: Pecskay et al., 1995). This area includes the Rodna and Bargău Mountains where many shallow intrusions (rhyolit.es. rhyodacites, dacites, andesites. microdiorites) penetrated either a Precambrian metamorphic basement or a Paleogene sedimentary one. The intrusions occur in two alignments parallel to the Transcarpathian Flysch Fault (Fig. 1). Most of the intrusive bodies contain enclaves. The presence and the abundance of the igneous enclaves depend on the petrographic type of the host. rock: they are rare in dacites. rhyodacites and rhyolites and quit-e abundam in andesites (especially in the quartziferous ones) and in microdiorites. Types of enclaves The studied enclaves can be separated (in a genetic classification) in four comprehensive groups: igneous enclaves. metamorphic enclaves, sedimentary enclaves. and xenocrysts. Each group, in its turn, can be divided. on the basis of petrographical and mineralogica! criteria, in several categories, as follows: (1) The igneous enclaves may be cognate enclaves or foreign enclaves. The cognate enclaves consist of glomeroporphyric mineral assemblages similar to the host rock with respect to their composition and origin. T he foreign enclaves are rocks which differ from the host. rock by their features. They may be andesites, basalls or microdiorites, modified to various degrees by a host rock-induced recrystallization; these enclaves "Paper presented at the International Congres of Vulcanology. lAVCEI-Capetown, July 1998. South Africa Institutul Geologic al României 68 E. NIȚOI et al. 1 - Location of the calc-alkaline intrusive magmatism in the general framework of the Carpatho-Pannonian area 1, calc-alkaline volcanic rocks: 2, Inner Carpathians; 3, Outer (flysch) Carpathians. represent rocks of the earliest magmatic events in the area, pierced by the magmasof the younger generations which crushed and transported them to the upper levels. (2) The metamorphic enclaves represent either regionali}' metamorphosed rocks or sedimentary rocks thermally metamorphosed by the host. magma. The enclaved regionally metamorphosed rocks may show a superposed contact metamorphism. The new parageneses added sillimanite, andalusite, K-feldspar, corun- dum and spinels to the older ones containing amphiboles, quartz, feldspars, biotite, gârneț, staurolite and kyanite. In t he carbonaceous sedimentary enclaves the contact metamorphism produced andradite vesuvian- ite and wollastonite. The general absence of quartz and muscovite as well as the common occurrence of the spinel and K- feldsparicorundum indicates a high-grade contact metamorphism of most of the feldspathic enclaves. The amphibolic enclaves seem to have been almost inert with respect to the host rock infiuence. The mica-rich enclaves usually show parțial melting. Two biotite generations have been observed in the metamorphic enclaves: a) An older one, with largely developed crystals decomposed along cleavage planes. It formed during the regional metamorphism and usually grew in conformity to the schistosity of the enclave. This biotite is associated with K-feldspar and spinel produced by its breakdown. b) A new biotite usually occurs near the contact with the host rock as tiny, rounded crystals (Pl. I, Fig. !)• Sillimanite is most frequently fibrolitic and commonly replaces feldspars (Pl. I, Figs. 2 and 3), seldom biotite (Pl. I, Fig. 4) and only excepționali}' andalusite or gârneț. Gârneț occurs as newly formed crystals or as overgrowths on older gârneț crystals. Spinel (Fe-rich) and corundum (Pi. I, Fig. 2) usually occur near the contact with the host rock, but may be present in the inner parts, too. Spinel occurring in the inner parts of the enclaves is more magnesian than the one near the margins. Andalusite is common only in a small sili of the Oala body, being scarce elsewhere. It forms porphyroblastic crystals, sometimes altered to a pinite mass. Noteworthy, some enclaves are surrounded by a. distinct border or a reaction corona. Considering their mineralogica! composition, these borders Institutul Geological României ENCLAVES IN THE EAST CARPATHIANS NEOGENE INTRUSIONS 69 Amphibole composition plotted in several classification diagrams. Fig. 4 - The Chemical composition of the biotite in Foster diagramme (1960). Institutul Geological României 70 E. NIȚOI et, al. qo^ooid^oolo • 04 04 • * *........H • JU 04 04 CO 04 04 04 H m>o4coin^^ O o- • oo • • m m o ’t m C4 • • O • O H..... O O o o o o o o O^r-M40'OHOO ^OOOOOHHH ^oH^o^toincNCAoi^ 2O4O4HO4O4HHMHO4H Ooioir-^omcomcn ojoicri^HcriOXdi d............... £O4HHO4HO4HH Table la Electron microprobe analyses of selected amphiboles (A-type) from the host rocks (Măgură Arsente, Măgură Cornii, Casariu, Meniu, Oala Sturzii structures) O • cri 04 > cn H • o* in (țj H.......H • • UHHrIHHHOOrIHH r'koooioipmooLn>Lf)> Qcoo40>incTiCOkDr-xrHoo tn......................... gHinmr-wcoHNin'tfin r-ir-Ir-Ir-1 H H H H H H Q H O H CO H • H 04 H H H g O O O O O O O O O O >C0^C0inHin(N(»'^O4 O O M in O (Ti ■ Q O kD co (1).........LO • [jq'^OHLPCTiCOHCOHHH H H H H H H H rl CO Oo^^or-ooooooo 04 OH 04 O O . . [q O O O O m Ooo<^cno4HHcoa\o4^H 04 in ro • • kO LH 00 O H rH • • 04 04....... ^mcoHHcoHcno4coHco H H H H H H H H H csjincomooHcoi>ooM*com O m > o oo • h cn in m1 •H............O . • • . H H H H 04 H H 04 H 04 H r-wcoinko^^^ O cn ko cn in •oi^h nj • • • • h • • • UHHOHHOHO H H H H H H H LEinipcnokDcoLn o ' H O O 00 0) ..........H SHO'O4e4inr4cnH H H H H H H oicncoininHM1^ OHomo4HmHoi ro OOLD^OOOO 04 in Q) • . fa o o m 0>rlOkO(NLD^ 04 m cn • cn o oi o H • • cn . . . . < m H 04 co 04 m H H H H H H 04^)04^004^0'00 Oocoipocnojw •H ••••••• HHOO04H04H 0q(N(r)^rlbO4k0>>mi> O oo h oo m1 ■ oo cn i> •h*,**h»«»**« cnono4cnHM m h co ENCLAVES IN THE EAST CARPATHIANS NEOGENE INTRUSIONS 71 oi oi co oi • oi d . . . o • o £ o o o o O d U CO H in oi ca Ol Ol kD Ol in Ol Ol Ol Ol Ol o Ol K O oi O CN % CA 00 H C0 co H in in kD kD o o 0) 8 Ol kD oî Ol CA in oi in in in in H 00 in H H cO H H O CN H in H • g O O O O O O ca oi O ca in Q) . . h cn ’f cn H Ol kD CA co in kD in co OH^COOO'OO oi • kD o oi O o • • o o o co OokDCACAoo^'f oi co o o co kO • H..........co H co co h co Ol Ol Ol CA O co rn oi •H • • • H o o o Ol Ol O 00 CO Ol o o o o oi in O o ■H cn in in oi oi in kD CA co Ol in in oi in oi in (AH tî< Oj • • O O O o in o O CA CA O Ol in oi o o o o T3 73 a a CO CO H CA • 00 in • • • h in in H H H kO (A kD CA in • CO • CO • • CO CO CO M ►q cu § co M oo CU M CU M KO cu a CU a co >1 cu a cu cu Ol O •H cn ko o* in • C0 kD CO kD • • • co in ko kD co co co co H M o co ca CQ Institutul Geological României E XIȚOI et al. COGNATEENCI AVES < m Institutul Geologic al României Xjgr/ ENCLAVES IN THE EAST CARPATHIANS NEOGENE INTRUSIONS 73 • Host rocks + Cognate enclaves Institutul Geological României I E. NIȚOl et ai. + Cognate enclaves Host rocks l'ig. 7 - Major element Harker variation diagrams for cognate enclaves and host rocks from Bargau and Rodna Mts. seem io be either secretions of the enclaves (quartz or amphibole rims of amphibolic enclaves) or of the host rocks (plagiocla.se. amphibole or pyroxene rims). The crystals in these rims are smaller than the phenocrysts in the host rocks or than the analogous crystals in the enclaves. Retrogressive rims (carbonate, epidote, chlorite) occur around severa! enclaves. Carbonate usually occurs near the host rock. Most of the metamorphic enclaves show petrographic similarities with the medium-grade Bretila Group and Rebra Group that crop out in the East Carpathians. Institutul Geological României ENCLAVES IN THE EAST CARPATHIANS NEOGENE INTRUSIONS 75 ( 3) The sedimentary enclaves are rocks from the sedimentary basement that have not undergone miner- aldgical transformations under the influence of the host rock. ( 4) The xenocrysts are represented by amphibole. quartz and gârneț crystals engulfed by the volcanic matrix. The amphiboles show reaction corronas formed of opaque minerais or pyroxenes (PI. II, Fig. 5). Quartz xenocrysts are usually corroded or have pyroxene rims (PI. II, Fig. 6, 7). Garnets may show resorbtion shapes or reaction rims formed of opaque minerais or retrogressive assemblages (bîotite-chlorite- epidote) (PI. II, Fig. 8; PI. III. Fig. 9). Mineralogica! features of host rocks and igneous enclaves Most of the host rocks and their igneous enclaves consist of the following minerais: The plagioclase is albite-type twinned, zoned (PI. III, Fig. 10) altered or not. with an A n-content of 42-70 %. It occurs either as euhedral to subhedral, 2-3 mm long crystals or as micronic, more or less idiomorphic microliths. In certain enclaves, a well developed symplektitic texture occurs at the plagioclase contact with other minerais of the rock. The amphibole is present in all the petrographic types including the host-rocks and enclaves. Four types of amphibole were found: - The A-type (PI. III, Figs. 11, 12) is the most common. It forms euhedral crystals, brown-greenish in colour, sometimes marginally opacitized, up to 1 cm in size. It was formed during the first stages of magma crystallization. Its Chemical composition (Table la) plots in the ferroan pargasite field [(NaCaO2Fe2+ AlSieAUOo» (011)2)] according to A1IV vs. Mg/(Mg+Fe2+) diagram in Figure 2. The mean composition is: SiO2=39.82-43.86; AI2O3=11.8I-15.53: MgO=11.68-15.26; 00=9.63-11.94; Na20= 1.66-2.47; Al=2.10- 2.69; mg=0.75. It was found in both host rocks and cognate enclaves. - The B-type is a poikilitic hornblende (PI. IV, Figs. 13, 14) found only in cognate enclaves and which has been formed during the lat.er stages. It includes earlier crys'-dlized idiomorphic pyroxenes or plagioclases. Its mineralogica! and Chemical features place it in the ferroan pargasite-tschermakite field (Fig. 2). The mean Chemical composition is: SiO2=45.26; AI20s=l 1.91: MgO=17.15; Ca0=11.31; Na2O=L92; K2O=0.74; mg=0.89: Al=2.00 (Table 1 b). - The C-type is a magnesiohastingsite found only in cognate enclaves (PI. IV, Fig. 15). Its colour is intense, with green pleochroic tints. The texture and the crystal habit indicate that it. has formed by the reaction of an earlier pyroxene with the residual magma, during a later stage of crystallization. Its mean Chemical composition is: SiO2=45.71; AI2O3=9.70; MgO=12.95; CaO=10.93; Na2O=1.47; K2O=0.47; mg=0.69; Alf = 1.67. (Table 1 b) - The D-type is a. green, fibrous actinolitic hornblende, grown in bundles at the contact between the magmatic enclaves and the host rock. The pyroxenes. Textural relations as well as the mineralogica! and Chemical parameters (Table 2, Fig. 3) distinguish two pyroxene generations: phenocrysts of a first. generation and small crystals of a second one. The phenocrysts (PI. IV, Fig. 16, PI. V, Fig. 17) and formed directiv from the magma and have the augite composition (En=43.14-44.96; Wo=44.07-46.06; Fs= 12.75-8.98: mg=86.27). The augite has been found in both enclaves and host rocks. The pyroxenes of the second generation (Pl. V, Figs. 18. 19) have a diopside composition: En=27.82-45.96; Wo=48.79-46.53; Fs=22.38-7.5; mg=56.46. They occur only in enclaves. The biotite was found mostly in the Măgură Cornii and Valea Vinului structures. It has grown in two generations: a first one (in host rocks-quartziferous andesites), occurring as idiomorphic, inclusion-free phenocrysts, is represented by a Fe2+-rich biotite (Pl. VI, Figs. 20, 21). The Chemical composition (Table 3, Fig. 4) of the phenocrysts shows high Fe and low Ca content. The second generation of biotite occurs only in enclaves (Pl. VI, Figs. 22, 23). The accessories. In most of the host rocks and enclaves, apatite and gârneț euhedral crystals and opaque minerais difficult to identify usually occur. Peti'ogenetic considerations The study of the genetic relations between enclaves and host rocks has been clone on 11 pairs enclave-host rock that belong to several subvolcanic structures: Măgura Arsente, Valea Vinului, Oala, Magurita, Heniu and Măgură Corni. The following remarks can be drawn: 1. The SiO2 content (Table 4) ranges between 43.92 % and 49.84 % in the enclaves and between 48.5 % and 58.06 % in the host rocks. In the I\2O vs. SiO2 and SiO2 vs. Na2O+K2O classification diagrams (Le Maitre et al., 1989) the enclaves plot in the field of low-K basalts (tholeiites) and the host rocks in the fields of andesites and medium-K basaltic andesites (Figs. 5 and 6). 76 E. NIȚQJ et al. 2. In t.he Harkers binary diagrams, both for cognate enclaves and host rocks (Si02 vs. AI2O3, CaO, \a-X). 1<2O. MgO and Fe2O3) show a linear evolutive trend for CaO. MgO and Na2O and a. wide dispersion of t he plots for FeO, Fe2O3 and A12O3 (Fig. 7) The. dispersion can be explained by the changes of the inițial inineralogical and Chemical features of the enclaves and host rocks under the physico-chemical and mecanica! reciproca! ini!uences. 3. In the FAM diagrams (Fig 8 - Irvine and Baragar, 1971 and Fig. 9 - Besson and Fonteilles, 1974), based on the elements less sensitive to the silica-induced dilution (Fe, Mg, Al, Mn) the features of the cognate enclaves are similar to those of the calc-alkaline melts and the features of t.he host rocks are similar to those of t he evoluted melts, intermediar}' between the calc-alkaline (I) and tholeiitic (II) types. I. The chemical and mineralogica! similarities of the phenocrysts (amphiboles, pyroxenes, plagioclases) from both enclaves and host. rocks, t.he modal and normative (CIPW) compositions support the idea of the existence of common petrological features as effect of a common origin. 5. We consider that the mafie magmatic enclaves (cognate enclaves) are formed during the earlier stages of magma evolulion, when its composition was close to a basaltic one. They are syncrystallized with the host rocks or postdate them. Conclusions The linear evolutive trend revealed by the major components and by the FeO/MgO ratios (0.26-0.49 in enclaves, 1.07-2.09 in host. rocks) support the conclusions obtained from the mineralogica! study. which sug- gest.s the existence of a single calc-alkaline hydrated magma (with 3-3.5 % water) with tholeiitic tendencies. It has formed in intermediate magmatic chambers, at depths of 15-20 km, at pressures of 6.43-6.83 kb and lemperatures of 700-800 °C. The pressures were determined using the Al-in-hornblende geothermometer: P(±5 kb)=-3.46 (±0.24)4-4.23 (±0.13) Al7 given by Johnson and Rutherford, 1989 (Fig. 10). Pressure val- ues determined for t he enclaves are consistent with those for the host rocks. We consider that the fractionate irysiallization of the hornblende exersized a significant infiuence on magma genesis and evolution. References Besson. M.. Fonteilles. M. (1974) Relationsentre le comportements contraste de l’alunnne et du fer dans la differenciation des series tholeiitique et calco-alcaline. Bull.Soc.mineral.Cristallogr., 97. p. 445-465. Irvine. T. N.. Baragar, W.R..A. (1971) A guide to the Chemical classification of the common volcanic rocks. Canadian Journal of Earlli Sciences, 8, p. 523-548. Johnson. M.C.. Rutherford. M. J. (1989) Experimental caii braț ion of the aluminium in hornblende geobarometer with application to long Valley Caldera (California) volcanic rocks. Geology, 17, p. 837-841. Pecskay. Z.. Edelstein, O., Seghedi, I.. Szakacs, Al., Kovacs, M.. Crihan. M., Bernard, A. (1995) K-Ar datingsof Neogene-Quaternary calc-alkaline volcanic rocks in Romania. Acta, voie., 7, p. 53-61 . Institutul Geological României P L A T E S Institutul Geological României Fig. 1 Fig. 2 Fig. 3 Fig. 4 Plate I — New biotite (black) occurring as tiny, rounded crystals (s - sillimanite; f - feldspar) — Fibrolitic sillimanite (s) around pinite aggregates (pseudomorplis on feldspars?) containing corundum crystals (c) — Sillimanite (s), corundum (c), spinel (black) and new biotite (b) in a feldspathic enclave (f-feldspar). — Sillimanite (s) grown on biotite (b) in a feldspathic enclave (f-feldspar). Institutul Geological României E. Nițoi ei al. Enclaves in the East Carpathians Neogene Intrusions Pl. 1 An. Inst. Geol. Rom. voi. 72. part II I nstitu Plate II Fig. 5 Atnphibole (hornblende) xenocryst with opaque minerals and pyroxene reaction corona. The host rock is a pyroxene and hornblende (Colibita structure). Fig. 6 — Gorroded quartz xenocrysts (Heniu structure). Fig. 7 - Quartz xenocryst with pyroxene (diopside) reaction rim (Heniu structure). Fig. 8 Gârneț, xenocryst with resorption shape (Colibita structures). Institutul Geological României E. NlȚOI el al. ENCLAVES IN THE EAST C-ARPATHIANS NEOGENE INTRUSIONS Pl. II An. Inst. Geol. Rom. voi. "2. part II Plate III Fig. 9 Gârneț xenocryst with reaction corona in the andesite host rock (Strejii structure). Fig. 10 — Zoned plagioclase phenocryst, unaltered and showing euhedral shape (center). (Valea Vinului structure) Fig. 11 — Zoned. euhedral A - type amphibole (ferroan. pargasite). in the andesitic host rock (Măgură Arsente structure). Fig. 12 —A-type amphibole (ferroan pargasite)). Institutul Geological României K. NlȚOI el al. ENCLAVES IN THE EAST CARPATHIANS NEOGENE INTRUSIONS PI. III An. Inst. Geol. Kom. voi. 72. part 11 nstitutul Geologic al Rc Plate IV Fig». 13. 14. 15 Poikilitichornblende (B-type) in cognateenclaves. The Chemical features place it in the ferroan, pargasite - tschermakite field. The host rocks is microdiorite (Arsente Structure). Fig. 16 — Primary pyroxene (augite) phenocryst. Institutul Geological României E. NiȚOiet al. Enclaves in the East Carpathians Neogene Intiwsions PI. IV An. Inst. Geol. Rom. voi. 72. part II nstitutul Geologic al R Plate V Fig. 17 Primary pyroxene phenocryst.. The host. rocks is an andesite. (Strejii structure). Figs. 18. 19 — Secondary generation pyroxene crystals (diopside), from an enclave (Dornisoara structures). Fig. 2o - First generation biotite (idiomorphic, inclusion-free) in quartz andesite host rock (Valea Vinului structure). E. Nițoi ei al. Enclaves in the; East Carpathians Neogene Intrusions Pl. V An. Inst. Geol. Bont. voi. ,2. part- II nstitutul Geologic al Ro J Plate VI Fig . Figs. 21 — First generation biotite (idiomorphic, inclusion-free) in quartz andesite host rock (Valea Vinului structure). 22. 23 — Biotite of the second generation from an enclave. Institutul Geological României E. Nițoi et al. Enclaves in the East Carpathians Neogene Intrusions Pl. VI IGR> An. Inst. Geol. Rom. voi. 72, part II Institutul Geological României INSTRUCȚIUNI PENTRU AUTORI ANUARUL INSTITUTULUI GEOLOGIC AL ROMÂNIEI publică contribuții științifice originale referitoare la acest domeniu. Vor fi acceptate numai lucrările care prezintă concis și clar informații noi. Manuscrisul va fi supus lecturii critice a unuia sau mai multor specialiști: după a doua revizie nesatisfăcătoare din partea autorilor va fi respins definitiv și nu va fi înapoiat. Manuscrisele trebuie prezentate, de regulă, în engleză sau franceză; cele prezentate în limba română trebuie să fie însoțite de un rezumat. în engleză sau franceză, de maximum 10 % din volumul manuscrisului. Lucrările trebuie depuse, pe disketă și text pe hârtie în două exemplare, la secretariatul Comitetului de redacție, inclusiv ilustrațiile în original. Manuscrisul trebuie să cuprindă: textul (cu o pagină de titlu, care este și prima pagină a lucrării), bibliografie, cuvinte cheie, abstract., ilustrații, explicații ale figurilor și planșelor, și un sumar cu scop tehnic. Se va adăuga o filă separată cu un colontithi de maxi- mum 60 semne și un sumar. în care se va indica ierarhia titlurilor din text în clasificarea zecimală (1; 1.1; 1.1.1). care nu trebuie să depășească patru categorii. Textul va fi predat pe disketă, format ASCII și două copii pe hârtie, cu un spațiu liber de 3 cm în partea stîngă a paginii și nu trebuie să depășească 10 pagini (inclusiv bibliografia și figurile). Prima pagină a textului va cuprinde: a) titlul lucrării (concis, dar informativ), cu un spațiu de 8 cm deasupra; b) numele întreg al autorului (autorilor); c) instituția (instituțiile) și adresa (adresele) pentru fiecare autor sau grup de autori; d) text. Notele de subsol se vor numerota consecutiv. Citările din text trebuie să includă numele autorului și anul publicării. Exemplu: lonescu (1970) sau (lonescu, 1970). Pentru doi autori: lonescu, Popescu (1969) sau (lonescu, Popescu, 1969). Pentru mai mult de doi autori: lonescu et al. (1980) sau (lonescu et al., 1980). Pentru lucrările care se află sub tipar, anul publicării va fi înlocuit cu ”in press”. Lucrările nepublicate și rapoartele vor fi citate în text ca și cele publicate. Abstractul, maximum 20 rînduri (pe filă separată), tre- buie să fie în limba engleză și să prezinte pe scurt, princi- palele rezultate și concluzii (nu o simplă listă cu subiecte abordate). Cuvintele cheie (maximum 10) trebuie să fie în limba engleză sau franceză, corespunzător limbii în care este lucrarea (sau abstractul, dacă textul este în română), prezentate în succesiune de la general la specific și dac- tilografiate pe pagina cu abstractul. bibliografia se prezintă în ordine alfabetică și crono- logică peut ru autorii cu mai mult, de o lucrare. Abrevierile titlului jurnalului sau ale editurii trebuie să fie conforme cu recomandările respectivelor publicații sau cu standard- ele internaționale. Exemple: a) jurnale: Giușcă, D. (1952) Contributions â l’etude cristallochi- miquedesniobat.es. An. Corn. Geol., XXIII, p. 259- 268. București. . Pavelescu, L. (1954) Contribuții la studiul mine- ralogic al zăcămîntului de la Mușca. Gonim. Acad. Rom.. IV. 11-12, p. 658-991, București. b) publicații speciale: Ștrand. T. (1972) The Norwegian Caledonides. p. 1- 20. In: Kulling. O., Ștrand, T. (eds.) Scandinavian Caledonides, 560 p., Interscience Publisher*. c) cărți: Bălan, M. (1976) Zăcămintele manganifere de la lacobcni. Ed. Acad. Rom., 132 p.. București. d) hărți: lonescu, 1.. Popescu. P., Georgescu, G. (1990) Geological Map of Romania. scale 1:50.000, sheet Cîmpulung. Inst. Geol. Geofiz., București. e) lucrări nepublicate sau rapoarte: Dumitrescu, D., lonescu, I., Moldoveanu, M. (1987) Report. Arch. I.G.R., București. Lucrările sau cărțile publicate în rusă, bulgară, sârbă etc. trebuie menționate în bibliografie transliterînd nu- mele și titlurile. Exemplu: Krasheninnikov, V. A., Basov. 1. A. (1968) Stratigrafiya kainozoia. Trudy GIN. 110. 208 p.. Nauka, Moskow. Ilustrațiile (figuri și planșe) trebuie numerotate și prezentate în original, pe coli separate (hîrtie de calc), bune pentru reprodus. Dimensiunea liniilor, a literelor și a simbolurilor pe figuri trebuie să fie suficient de mare pentru a putea fi citite cu ușurință după ce au fost re- duse. Dimensiunea originalului nu trebuie să depășească suprafața tipografică a paginii: lățimea coloanei 8 cm. lățimea paginii 16.5 cm. lungimea paginii 23 cm, pentru figuri, iar pentru planșele liniare nu trebuie să depășească dimensiunile unei pagini simple (16,5/23 cm) sau duble (23/33 cm) și trebuie să fie autoexplicati vă (să includă titlul, autori, explicație etc.). Scară grafică obligatorie. Ilustrațiile fotografice (numai alb-negru) trebuie să fie clare, cu contrast bun și grupate pe planșe de 16/23 cm. In cadrul fiecărei planșe numărătoarea fotografiilor se repetă (de. ex. PL 1, fig. 1. Pl. II. fig. 1). Tabelele vor fi numerotate și vor avea un titlu. Di- mensiunea originală a tabelelor trebuie să corespundă di- mensiunilor tipografice menționate mai sus (8/16,5 sau 16.5/23). Autorii vor primi un singur set de corectură, pe care trebuie să-l înapoieze, cu corecturile corespunzătoare, după 10 zile de la primire. Numai greșelile de tipar tre- buie corectate; nu sînt acceptate modificări. Autorii vor primi gratuit 30 de extrase pentru fiecare lucrare. Comitetul de redacție INSTRUCTIONS TO AUTHORS ANUARUL INSTITUTULUI GEOLOGIC AL ROMÂNIEI publishes original scientific contributions dealing with any subject of this field. Only papers presenting concisely and clearly new infor- mat ion will be accepted. The manuscript will be submit- ted for criticai lecture to one or severa! advisers. Papers will be definitely rejected after a second unsatisfactory revision by the authors. The manuscripts will not be re- t urned to the authors even if rejected. Manuscripts are prefered in English or French. Manuscripts subinitted in Romanian will be accompanied by an abstract in English or French (maximum 10 per cent of the manuscript volume). Papers should be subinitted on diskette and typed text in duplicate to the secretary of the Editorial Board, including the reproduction ready original figures. The manuscript should comprise: text (with a title page which is the first. page of it), references, key words, abstract, illustrations, captions and a summary for technical pur- poses. Author(s) should add a separate sheet with a short title (colontitle) of maximum 60 strokes and a summary indicating the hierarchy of headings from the text listed in decimal classification (1; 1.1; 1.1.1) but not exceeding four categories. Text should be on diskette, format ASCII and 2 copies. holding an empt.y place of 3 cm on the left side of the page. T he text cannot exceed 10 typewritten pages (including references and figures). Front page (first page of the text) should comprise: a) t itle of the paper (concise but informative) with an empty space of 8 cm above it; b) full naine(s) of the author(s); c) institution(s) and address(es) for each author or group of authors; d) text. Footnot.es should be numbered consequtively. Citations in the text should include the name of the au- thor and the publication year. Example: lonescu (1970) or (lonescu, 1970). For two authors: lonescu, Popescu (1969) or (lonescu, Popescu, 1969). For more than two authors: lonescu et al. (1980) or (lonescu et al., 1980). For papers which are in course of prinț the publication year will be replaced by ”in press”. Unpublished papers or reports will be cited in the text like the published ones. Abstract, of maximum 20 lines (on separate sheet), must be in English, summarizing the main results and conclusions (not a simple listing of topics). Key words (max. 10 items), in English or French, fol- lowing the language used in the text (or the Resume if the text is in Romanian). given in succession from general to specific, should be typed on the abstract page. References should be typed in double-line spacing, listed in alphabetical order and chronological order for authors with more than one reference. Abbreviations of journals or publishing houses should be in accordance with the recommendations of the respective publications or with the internațional practice. Examples: a) journals: Giușcă, D. (1952) Contributions â l’etude cristallochi- mique des niobates. An. Corn. Geol., XXIII, p. 259- 268, București. , Pavelescu, L. (1954) Contribuții la studiul mine- ralogic al zăcămîntului de la Mușca. Comni. Acad. Rom., IV, 11-12, p. 658-991, București. b) special issues: Ștrand. T. (1972) The Norwegian Caledonides. p. 1 20. In: Kulling, O., Ștrand, T. (eds.) Scandinavian Caledonides, 560 p., Interscience Publishers. c) books: Bălan, M. (1976) Zăcămintele manganifere de la lacobeni. Ed. Acad. Rom., 132 p., București. d) maps: lonescu, I.. Popescu, P.. Georgescu. G. (1990) Geological Map of Romania, scale 1:50,000, sheet Câmpulung. Inst. Geol. Geofiz.. București. e) unpublished papers or reports: Dumitrescu, D., lonescu, I., Moldoveanu. M. (1987) Report. Arch. Inst. Geol. Geofiz., București. Papers or books published in Russian. Bulgarian or Serbian etc. should be mentioned in the references transliterating the name and titles. Example: Krasheninnikov, V. A., Basov, I. A. (1968) Stratigrafiya kainozoia. Trudy GIN, 410, 208 p,, Nauka, Moskow. 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Author(s) will receive only one set of preprim proofs which must be retumed, with corrections, 10 days after receiving them. Only printing errors should be corrected, no changes in the text- can be accepted. Thirty oflprints of each paper are supplied to the au- t.hor(s) free of charge. Editorial Board jA Institutul G igr/ eologic al României Toate drepturile rezervate editurii Institutului Geologic al României All rights reserved to the Geological Institute of Romania Editat cu sprijinul Agenției Naționale pentru Știință, Tehnologie și Inovare - Colegiul Consultativ pentru Cercetare Științifică și Dezvoltare Tehnologică Edited with the support of the National Agency for Science, Tehnology and Innovation - Advisory Board for Scientific Research and Technologic Development Translation and language review by: Adriana Năstase Editorial Staff: Georgeta Borlea, Cristian Toth Illustration: Paraschiv Toader Printing: G. Bădulescu, N. Păleanu, F. Dumitru, P. Jurjea, C. Alhu Institutul Geological României