[Show abstract][Hide abstract] ABSTRACT: Although no undoubted oceanic crustal rock complexes of Penninic affinity participate in the present surface structure of the Western Carpathians, indirect lines of evidence suggest prolongation of the South Penninic-Vahic oceanic tract into the ancient Carpathians. The sedimentary record of both the syn-rift and syn-orogenic clastic deposits reveal their origin between the outer Tatric (Austroalpine) and the inner Oravic (Middle Penninic) margins. The rifting regime is exemplified by the normal fault-related scarp breccias of the Jurassic Borinka Unit in the Malé Karpaty Mts., which are characterized by local, gradually denuded source areas. Two other regions provide examples of a contractional regime, both related to shortening and closure of the Vahic oceanic domain. The Belice Unit in the Považský Inovec Mts. includes Upper Jurassic-Lower Cretaceous eupelagic, mostly siliceous deposits and a thickening-upwards Senonian sequence of turbiditic sandstones, conglomerates and chaotic breccias. It is inferred that this succession represents the sedimentary cover of oceanic crust approaching a trench, its incorporation in the accretionary complex and finally underthrusting below the outer Tatric margin. In the Oravic units of the Pieniny Klippen Belt, deep-marine conglomerate/breccia bodies with olistoliths indicate collision-related thrust stacking that started from the Maastrichtian (Gregorianka Breccia of the Sub-Pieniny Unit) and terminated with the Lower Eocene Milpoš Breccia in the Šariš Unit. In addition, a tentative recycling scheme of "exotic" clastic material from mid-Cretaceous conglomerates of the Klape Unit to various Klippen Belt units is outlined. This material is considered to be unrelated to the Vahic oceanic realm and its closure, and likely represents erosional products of more distant orogenic zones.
No preview · Article · Dec 2012 · Geological Quarterly
[Show abstract][Hide abstract] ABSTRACT: The Meliata Mélange and the origin of the different blocks in a cherty matrix (radiolarites, cherty limestones, cherty marls, argillaceous marls) are crucial not only for the interpretation of the geodynamic history of the south--eastern part of the Western Carpathians. Similar mélange complexes do exist in the southern Northern Calcareous Alps and in the Dinarides, Albanides and Hellenides. The Meliata Mélange, and especially its type locality at the Muráň river in the small village Meliata (Slovak Karst Mts.), stands as a synonym for the suture of the Meliata Ocean. According to the widely accepted paleogeographic reconstructions, the Meliata Ocean, sometimes also named Meliata-Hallstatt Ocean, should strike originally from the Northern Calcareous Alps to the Western Carpathians. In this classical model, the Northern Calcareous Alps and the Western Carpathians form its northern shelf, whereas the Transdanubian Range and the Bükk Mts. should have formed its southern margin. On the contrary in our model, which is based on investigations of different mélanges in the Alpine/Carpathian/Dinaride realm, the "Meliata Ocean" does not represent an independent ocean, but the northernmost part of the single Neotethys Ocean. This started to open in the Anisian and was partly closed in the late Middle Jurassic times. During this orogenic phase, which formed the Neotethyan Belt, several types of ophiolitic and radiolaritic mélanges were created. One of them is the Meliata Mélange. However, the understanding and interpretation of the Meliata Mélange differ in the literature and no clear definition of the Meliata Mélange was presented until now. Consequently, an exact definition of a succession or unit should start at the type locality located tectonically south-west and above the Gemeric Superunit, which has the "Meliata Mélange" remnants preserved from both sides. This fact has led some authors to the opinions about two branches of the Meliata Ocean surrounding the Gemeric Superunit, whereas others inferred that the northern occurrences do not represent a true suture, but they were transported to its recent position tectonically by thrusting (obduction). By this, an exact definition of the Meliata Mélange will not only lead to a better understanding of the geology of the southeastern Western Carpathians, it will also help for a better understanding and reconstruction of the geodynamic processes in the whole Neotethys realm. For that reason we have started with a reinvestigation of the type-locality, particularly the Late Middle Jurassic matrix between the olistostromes and slide blocks of the upper part of the succession recognized in earlier investigations. The lower part of the type section was interpreted as a continuous Anisian to Carnian sequence originally. A sample from the basal part of the section, below the Ladinian cherty limestones and radiolarites and above the Anisian limestones, yielded the Callovian to Early Oxfordian age indicated by the microfacies resembling the silicified Bositra limestone with radiolarians. In the upper part of the Meliata type section, several grey limestone and dolomite fragments resting in a late Middle Jurassic sedimentary matrix occur. Besides Carnian limestones, also the Norian grey limestones occur that represent components derived from the typical grey Hallstatt facies. The different carbonate blocks in the Jurassic matrix show also different thermal overprint based on the Conodont Colour Alteration Index measurements, indicating transported metamorphism. Ophiolite components and slides are missing in the Meliata type section, but occur in the mélange areas in the nearby surroundings of the village. In fact, the Meliata Mélange represents originally a deep-water basin fill in front of advancing ophiolite and sedimentary cover nappes, which was later deformed by incorporation in the nappe stack. As a result, a typical mélange was formed. Acknowledgements. The authors acknowledge the financial support from the APVV and OEAD agencies (bilateral projects SK-AT-0014-10 and SK 04/2011).
[Show abstract][Hide abstract] ABSTRACT: Conference title - 9. Vyrocny predvianocny seminar Slovenskej geologickej spolocnosti--9th Annual seminar of the Slovak Geological Society, Copyright - GeoRef in Process, Copyright 2013, American Geosciences Institute. After editing and indexing, this record will be added to Georef., Language of summary - Undetermined, Pages - 493-494, ProQuest ID - 885317512, SubjectsTermNotLitGenreText - ArcGIS; cartography; Central Europe; digital cartography; digital terrain models; Europe; geographic information systems; igneous rocks; information systems; mapping; Neresnica Catchment; Neresnica Slovakia; Slovakia; volcanic rocks, Last updated - 2012-12-13, CODEN - MSLOBI, Corporate institution author - Bagelova, A; Nemeth, Zoltan; Plasienka, Dusan; Simon, Ladislav; Kohut, Milan; Iglarova, Lubica; Moravcova, Martina, DOI - 600528-17; 0369-2086; 1338-3523; MSLOBI
[Show abstract][Hide abstract] ABSTRACT: We present new zircon fission-track (ZFT) data from Variscan granitoid bodies in the Veporic (footwall unit) and Gemeric (hangingwall unit) thick-skinned nappe sheets of the Central Western Carpathians. All samples show Late Cretaceous to earliest Paleogene cooling ZFT ages, which contribute to constraining the low-temperature exhumation history of the Vepor-Gemer Belt. Four granite samples from the western part of the Gemericum near the contact with the underlying Veporicum provided central ZFT ages between 70.4 Ã‚Â± 5.4 and 74.7 Ã‚Â± 5.6 Ma. One sample from this area shows an older age of 87.7 Ã‚Â± 5.9 Ma, possibly owing to its higher structural position. One remoter sample from the SE part of the Gemeric Unit has 61.7 Ã‚Â± 3.4 Ma central ZFT age, which probably reflects exhumation associated with a younger compressional tectonic event in that area. One sample from the centre of the Veporic metamorphic core complex yielded a cooling age 64.9 Ã‚Â± 4.8 Ma. However, most of these samples exhibit an internal age scatter pointing to complex cooling and exhumation history influenced by a slow passage through the zircon partial annealing zone and/or reheating brought about by the Cretaceous Rochovce granite intrusion. In spite of this, the acquired ages generally match the exhumation trend of the Veporic metamorphic core complex.
Preview · Article · Jul 2007 · Journal of Geosciences
[Show abstract][Hide abstract] ABSTRACT: Tectonic activity during the Miocene exhumation of the Tatra granitoid basement resulted in frictional melting of granite. The activity marks the early stages of the faulting that is responsible for uplift of the High Tatras. As indicated by pre-existing cataclasite metamorphic mineral assemblages, the ambient pressure was about 250–300 MPa, corresponding to depths between 10 and 12 km. The pseudotachylytes are Fe rich, highly oxidized and crystalline. The matrix composition suggests disequilibrium partial melting of a biotite-dominated assemblage. Oxygen isotopic compositions of a pseudotachylyte sample and its constituent minerals show equilibration with the host granodiorite and allow for the introduction of oxidizing external water rather than oxidation as a result of the dissociation of free water liberated during melting. The kinetic information extracted from hematite crystal-size distributions (CSDs) that are preserved in feldspathic matrices shows that crystals in most places were accumulated while the system was open. The melt was highly mobile and prone to strong differentiation. The hematite crystals reach a maximum of 26 vol. % (45 wt % Fe 2 O 3 ). In rare places where the flow ceased, the system became closed and produced distinct CSDs. The longest apparent crystallization times (90 s) are recorded mostly in pools in the central parts of the pseudotachylytes whereas the shortest times (10 s) come from rims and tips of fractures. The estimated hematite growth rate was about five orders of magnitude higher than that of ilmenite in lava lakes. Such extreme crystallization rates result from high undercoolings associated with high cooling rates. Very high cooling rates are promoted by the extremely high surface/volume ratios of the pseudotachylyte sheets.
Full-text · Article · May 2003 · Journal of Petrology
[Show abstract][Hide abstract] ABSTRACT: Alpine low-grade metamorphism related to Cretaceous orogeny has been investigated in the metasediments of the Permo-Mesozoic cover in the Veporic unit, Western Carpathians. Scythian metaquartzites, slates, schists and Middle to Late Triassic metacarbonate sediments were studied by means of optical, XRD and electrone microprobe methods. Metaclastic rocks contain mainly white mica and quartz. K-feldspar and albite are present in various amounts and chlorite can be found only sporadically in few samples. Tourmaline is the main accessory mineral. Metacarbonates are composed of recrystallized calcite and additionally dolomite, albite, K-feldspar, quartz, white mica and chlorite are present. Metaclastic rocks and metacarbonates show metamorphic grade of upper anchizonal to epizonal (greenschist facies) conditions according to the illite crystallinity (IC) measurements. IC increases with increasing celadonite content of white K-mica in studied samples. Chlorite thermometry yields a temperature of 310-330 °C in the northern part and 335-380 °C in the central and eastern part of the Veporic unit. Although the chlorite thermometry is mostly inaccurate in sedimentary rocks, since it was calibrated for volcanic rocks, the increasing trend of metamorphic temperatures in the studied units is obvious and corresponds with the obtained phyllosilicate crystallinity data. A pressure of 4-4.5 kbar (380 °C) has been obtained from the white mica, K-feldspar and biotite-bearing rocks using an intersection of the reaction: 3Cel = Phl + 2Kfs + 3Qtz + 2H2O with the chlorite geothermometer. These results suggest higher temperature and lower pressure of Alpine low-grade metamorphism than previous estimates. The P-T conditions of Alpine low-grade metamorphism in the Veporic unit are in good agreement with observed deformational microtextures.
[Show abstract][Hide abstract] ABSTRACT: This study presents the first preliminary U-Pb zircon data on tin-bearing S-type granites from the Gemeric unit of the Western Carpathians (Slovakia). U-Pb single zircon dating controlled by cathodoluminescence suggests crystallization of the Gemeric granites during Permian to Early Triassic (303-241 Ma) time. Post-crystallization, low-temperature metamorphic overprint is reflected by partial Pb loss in zircons. These Gemeric granites are younger than the highly fractionated, S- type, tin- and rare-element-bearing leucogranites in the European Variscides. They may have resulted from partial melting, triggered by increased heat flow from the mantle below the continental crust, and most probably intruded during the post-collisional extension and initial rifting of the Variscan orogenic belt. During Alpine orogeny, the Gemeric granites were affected by a low-temperature deformation and metamorphism.