MIDDLE-LATE TRIASSIC 40Ar/39Ar HORNBLENDE AGES FOR EARLY INTRUSIONS WITHIN THE DITRAU ALKALINE MASSIF, RUMANIA: IMPLICATIONS FOR ALPINE RIFTING IN THE CARPATHIAN OROGEN
Abstract: Multigrain hornblende concentrates from two samples of massive gabbro and diorite collected within „early“ intrusive phases of the Ditrau alkaline complex (Rumania) record well-defined 36Ar/40Ar vs. 39Ar/40Ar plateau isotope correlation ages of 231.5 ± 0.1 Ma and 227.1 ± 0.1 Ma; 2σ intralaboratory error). These are interpreted as dating relatively rapid post-magmatic cooling at high crustal levels following pluton emplacement in the Middle-Late Triassic. The magmatic activity predated Early Jurassic rifting in the Eastern Carpathian orogen.
THE EVOLUTION OF THE NEOGENE VOLCANISM IN THE APUSENI MOUNTAINS (RUMANIA): CONSTRAINTS FROM NEW K-Ar DATA
Abstract: New K-Ar data from the Apuseni Mountains Neogene volcanic area are presented. When combined with geological and magnetic polarity data, the new data clarify the duration and evolution of this volcanic area. They show that the Neogene volcanic activity took place during the Late Badenian-Pannonian (15–7 Ma). The beginning of calc-alkaline andesitic volcanism (around 15–13 Ma) had an explosive character giving a widespread volcano-sedimentary formation. The volcanic activity reached the paroxysm during the Sarmatian (13.5–11 Ma), when thick lava flows and large volcanic structures were emplaced. This activity decreased in the Pannonian (10–7 Ma) and was restricted to the central and northeastern parts of the studied area. In the central part, the volcanic activity stopped in the Early Pannonian (10 Ma), while in the northeastern part it lasted until the Late Pannonian (7 Ma). The volcanic products are covered by pure sedimentary formations in only a few parts of the area. During all this time, tectonic activity played an important role in the basin’s development and volcanic processes.
SEMIDUCTILE DEFORMATION IN PELAGIC LIMESTONES AT DIAGENETIC CONDITIONS
Abstract: Semiductile to ductile deformation phenomena within unmetamorphic, fine-grained, pelagic limestones of the Northern Calcareous Alps (NCA) in the Eastern Alps were studied. The investigated pelagic limestones include the Triassic Hallstatt Limestone, the Liassic Adnet Limestone, the Middle Jurassic Strubberg Marl and the Upper Jurassic Oberalm Limestone. These pelagic limestones and marls display structures related to semiductile to ductile deformation, including shear planes, solution seams, stylolites and dynamic recrystallisation similar to structures in protomylonites due to strata-parallel simple shear. The structures preferentially developed along clay-rich layers and along boundaries between more competent marly limestones showing a protomylonitic appearence due to disjunctive anastomosing foliation. Along the boundaries aragonite and fine-grained calcite were dissolved and insoluble clay minerals were concentrated. Increasing strain resulted in the development of a penetrative foliation, generating S-C fabrics even within competent limestone layers. Furthermore, mesoscale out-of-sequence shear planes caused decomposition of competent limestone layers into clasts and nodules. These clasts acted as rigid objects within a more viscous, argillaceous matrix. When ideally oriented, asymmetric pressure shadows were generated around these nodules and σ-clasts were developed. The transition from massive limestone beds to nodular layers depends on silt and clay contents. While limestones with low clay content were structurally resistant to deformation, clay-rich limestones were easily deformed. The Adnet and Hallstatt limestones formed decollement horizons accomodating high strain during Cretaceous nappe stacking and thrusting within the NCA, while the Strubberg and Oberalm limestones were involved during Tertiary transpressive overprint in large strike-slip faults and thrusting within an associated triangle structure.
DIAGENESIS AND POROSITY OF THE UPPER TRIASSIC CARBONATES OF THE PRE- NEOGENE VIENNA BASIN BASEMENT
Abstract: The Upper Triassic carbonates of the Opponitz Formation and Hauptdolomit Formation represent reservoir rocks of gas deposits in the basement of the Vienna Basin Neogene fill. During study of the reservoir rock properties of dolomites in the well Kuklov-3 (K-3) significant variations in porosity as a result of late diagenesis processes in buried sediment were found. On the basis of petrographical, SEM and mineralogical-geochemical methods, we identified neomorphic calcite layers, also found in the Kuklov-4 (K-4) well. Coarse crystallized calcite crystals are idiomorphic (e.g. ditrigonal scalenohedron). They have a relatively high content of Sr, Fe and Na, and decreased isotopic ratio of O (δ18 O: -6 to -9 ‰) or also C (δ13 C: -0.7 up to +1.8 ‰) in comparison with values in dolomites (δ18 O: -4.8 up to ; 1.3 or also δ13 C: 0.1 to +4.1 ‰) or also in limestones (mostly δ18 O: -3.9 to -3.6 ‰). Microstructural analysis indicates that they substitute dolomites as a result of dedolomitization under conditions of deep burial. Diagenesis under conditions of deep burial results in forming of new minerals such as kaolinite, pyrite and illite. The observed changes (increasing) of reservoir rocks porosity of dolomites both in the well K-3 and K-4 (at the depth of 3660 to 3830 m) were caused by diagenetic processes taking place in the deep burial environment and these processes were probably limited to a layer of (originally dolomitic) breccias.
NEW DATA ON ”PLUMOSITE” AND OTHER SULPHOSALT MINERALS FROM THE HERJA HYDROTHERMAL VEIN DEPOSIT, BAIA MARE DISTRICT, RUMANIA
Abstract: Compositional data on a range of sulphide and sulphosalt minerals from the hydrothermal vein deposit of Herja in the Baia Mare metallogenic area are presented. The presence of zinkenite, chalcostibite, diaphorite, fülöppite, boulangerite, bournonite, electrum and manganite are confirmed in the Herja ores for the first time. In addition, compositions close to veenite, twinnite and heteromorphite have been identified — possibly representing the first report of these minerals on Romanian territory. Fibrous Sb-sulphosalts, which are trace phases in massive polymetallic ores and are the main component of the abundant vugs and cavities, are dominantly jamesonite, although boulangerite, berthierite and zinkenite are also present in lesser amounts. Arsenopyrite, associated with the Sb-sulphosalts is commonly enriched in Sb (to 6 wt. %). Fahlore phases were determined to be tetrahedrite, with Ag contents ranging from 7 to 20 wt. %. All Sb-sulphosalts are free of As. The loose felty matted masses of acicular needles, "plumosite", which occur widely throughout the vein systems are confirmed to be jamesonite. This mineral is characterised by a conspicuous Mn content, equivalent to 4–8 % mol. % benavidesite. This has been partially confirmed by X-Ray diffraction patterns, which showed a slight shift from those of some reference patterns for (Mn-free) jamesonite. However, a quantitative correlation between cell parameters and extent of Mn substitution is prohibited by discrepancies in the various peak patterns, resulting from differing experimental conditions. Although "plumosite" has been regarded as synonymous with boulangerite in recent years, it is proposed that the descriptive name "plumosite" be used for all such felted masses of Pb-Sb sulphosalts, including those with the compositions of jamesonite and berthierite. No supportive evidence for the existence of the problematic mineral parajamesonite was found in the examined samples. Geothermometry based on the S-isotope compositions of coexisting pyrite-galena pairs indicated temperatures of 417 ± 75 °C and 320 ± 70 °C, which are regarded as close to the maximum temperatures at the onset of mineralization. The stibnite and sulphosalt parageneses, however, are believed to have formed at temperatures below 220 °C.
EOCENE ANASCAN BRYOZOA FROM NEW LOCALITIES IN THE WESTERN CARPATHIANS, SLOVAKIA
Abstract: The paper concerns all Eocene anascan Bryozoa known from Slovakia. New bryozoan associations from Strba and Poluvsie are studied and described. A total of 10 taxa, newly found in Slovakia are described, the remainder are listed.
