Eclogite facies metaultramafite from the Veporic Unit (Western Carpathians, Slovakia)
Abstract: Metaultramafic rocks closely associated with eclogites in the Veporic unit of the Western Carpathians record a complex P–T evolution, including the effects of high-pressure (HP) metamorphism. The investigated metaultramafite is chemically similar to pyroxenite, has a fine- to medium-grained texture, is composed predominantly of olivine and amphibole, and contains minor amounts of garnet, orthopyroxene, spinel, chlorite, ilmenite and carbonates. The high-pressure mineral assemblage is garnet (XMg = 0.46–0.47) + olivine (XMg = 0.71–0.73) + low-Al orthopyroxene (XMg = 0.77–0.78; Al = 0.02–0.03 apfu) + ilmenite + chlorite (XMg = 0.87–0.89) + Cr-spinel. Chromium-rich spinel is most likely a relict from the pre-HP metamorphic stage, possibly of magmatic origin. Calculations using a garnet–orthopyroxene Fe–Mg exchange thermometer, Al-in-orthopyroxene barometer, and thermodynamic modelling in the system SiO2–TiO2– Al2O3–FeO–MgO–CaO–H2O indicate that the peak conditions of metamorphism reached 2.4±0.4 GPa and 702±20 °C. Subsequent decompression and retrogression is recorded by the formation of aluminous orthopyroxene, replacement of garnet by symplectites of Al-spinel and amphibole (hornblende), transformation of Cr-spinel to Al-spinel and formation of abundant amphibole in the matrix. Metaultramafic rocks in the Veporic unit thus provide evidence, in addition to that from associated eclogites, for high-pressure metamorphism in the pre-Alpine basement of the Western Carpathians, which is most likely of Variscan age.
Mineralogy, geochemistry and classification of the new Smolenice iron meteorite from Slovakia
Abstract: A single 13.95 kg mass of a slightly weathered iron meteorite was found in the forest near Smolenice (48°31.2’N, 17°23.9’E; Trnava County, Slovakia). The bulk chemical composition (in wt. %) is: Fe 88.78, Ni 8.16, Co 0.38, P 0.05, S˂0.006 and (in μg/g): Ge˂0.18, Ir 1.67, Ga 1.80, Cr 87.3, Cu 135.1, As 4.52, Mo 5.82, Sn 1.53, W 0.56, Re 0.18, Ru 3.56, Rh 0.90, Pd 4.12, Pt 5.35, Au 1.19, Zn˂5, B˂0.68, Pb˂0.06. Bulk geochemistry, and Ni, Ga, Ge and Ir contents in particular suggest that the meteorite is an octahedrite belonging to the IVA group. The average thickness of kamacite lamellae is 0.22 mm, ranking it as fine octahedrite (Of). The mineral composition is simple, the most abundant minerals being iron (kamacite) (5.16–7.36 wt. % Ni) followed by taenite (16.73–33.93 wt. % Ni). Troilite nodules and daubréelite inclusions and thin veinlets are rare. The Widmanstätten pattern is uniform across the meteorite and plessite structure is developed locally. Analyses of cosmogenic radionuclides (14C and 26Al) indicate that the radius of the Smolenice meteorite could be 30±10 cm and its terrestrial age 11±2 kyr.
Regional low-temperature fluid flow indicated by quartz mineralization in Silesicum, NE Bohemian massif
Abstract: The crystalline rocks of the Silesicum unit of the Bohemian Massif host two principal types of hydrothermal quartz veins. Veins associated with granitoids are primarily quartz with wollastonite and epidote and accompanied by hydrothermal alteration of host rocks whereas others are of the more complex “Alpine-type”. L + V + S (liquid + vapour + solid phase) fluid inclusions within quartz crystals contain muscovite and ± calcite (± haematite) as solid phases and homogenisation temperatures are between 124 and 176 °C. Trapped fluids are uniformly of the H2O–NaCl–CaCl2 ± MgCl2 ± KCl system with a salinity between 9.1 and 26.8 mass % (NaCl + CaCl2). The variable Na/Ca ratios result from different intensity of fluid-rock reactions. The ubiquitous muscovite is a product of fluid-rock interactions. Oxygen isotope evidence indicates that the fluids were a mixture of meteoric and marine waters in deep regional-scale convection systems. The studied type of fluids represents a post-Variscan hydrothermal system and shows the extent of migration pathways in the upper crust on the north-eastern edge of the Bohemian Massif.
U–Pb LA–ICP–MS dating of zoned zircons from the Greater Caucasus pre-Alpine crystalline basement: Evidence for Cadomian to Late Variscan evolution
Abstract: Here we report U–Pb zircon age data, obtained using LA–ICP–MS, from a total of 14 rocks of the Pass and Elbrus sub-zones of the Main Range Zone of the Greater Caucasus, which differ quite significantly from each other in composition of sedimentary and igneous rocks. Both exotic (detrital) zircons, and those formed within the Greater Caucasus are revealed. The ages of detrital zircons range from 2981 to 668 Ma. On the basis of weighted mean age data among in situ zircons from meta-sedimentary rocks in both sub-zones figures of 626± 2 Ma and 627± 19 Ma were detected, which corresponds to the earliest – Cadomian stage of high temperature regional metamorphism. From meta-sedimentary rocks of the Elbrus sub-zone figures – 461±5.3 Ma, 457±12 Ma indicate manifestation of the Ordovician (tectonically associated with Caledonian orogeny) stage of high temperature prograde regional metamorphism. Figures from granitoid rocks of both sub-zones – 454±9 Ma, 468±5 Ma and 471.7±4.6 Ma were obtained, which also correspond to the Caledonian stage of synmetamorphic granitoid formation. Besides, figures from the meta-sedimentary rocks of the Pass sub-zone – 312.5±4 Ma, 317.0±8.3 Ma correspond to Late Variscan regressive regional metamorphism. In addition, figures obtained from the granitoid rocks of both sub-zones – 309±8 Ma, 310.9 Ma, 325±4 Ma, 311±5.9 Ma and 357±5.9 Ma correspond to the Late Variscan stage of synmetamorphic granitoid formation. These results are in good agreement with geological and petrological data for the Greater Caucasus.
Tanystropheus and other archosauromorph reptile remains from the Middle and Late Triassic of Villány (Villány Hills, Hungary)
Abstract: Tanystropheus and other possible archosauromorph fossils have been discovered from Middle to Upper Triassic shallow marine sedimentary sections in Villány (Villány Hills, southern Hungary). Four fragmentary cervical vertebrae can be assigned to Tanystropheus sp. based on characteristic features including the strongly elongate and hollow vertebral body with extremely reduced neural spine. Besides the cervicals, various teeth, classified into four different morphotypes including longitudinally striated, carinated and ziphodont ones, are thought to belong to archosauromorphs, since they markedly differ from the frequently found teeth of fish and sauropterygians. In addition, three enigmatic cranial bones that might represent some circumorbital elements, have been found as well, and are referred to here as Sauropsida indet. These fossils, originated from the same tectonic unit as those from the Anisian of Bihor (Romania), are of great importance for a better understanding of the poorly known semi-aquatic to terrestrial vertebrate fauna of the Middle to Late Triassic of central Europe
Zircon U–Pb geochronology from Permian rocks of the Tribeč Mts. (Western Carpathians, Slovakia)
Abstract: U–Pb dating of magmatic zircons from the Permian basaltic metaandesites/metabasalts of the Tribeč Mts. yielded the Concordia ages of 263.1±2.6 Ma, which correspond to the Guadalupian Epoch in the time span of the uppermost Wordian/Capitanian Stages. These magmatic zircon ages clearly document the timing of the Mid-Permian lithospheric extension in the internal zone of the Variscan fragments in the Western Carpathians. The studied volcanic rocks with the associated metasediments belong to the Veporic Unit that overthrusts the Tatric Unit. The considered sequence was correlated with the Northern Veporic Permian rocks from the Čierťaž Mts. From the geochemical point of view, the studied volcanic rocks have a calc-alkaline magmatic trend with an affinity to continental within-plate tectonic setting, linked to the post-orogenic lithospheric extension. The detrital zircon population, obtained from the associated arkosic metagreywackes, displays mainly Tournaisian and Ediacaran zircon ages in the range of 342–367 and 546–631 Ma, respectively. Only a small number of Cambrian/Ordovician (499–466 Ma), Tonian (720–1000 Ma) and Paleoproterozoic/Neoarchean (~1.9 Ga and ~2.5 Ga) zircon ages were determined. The similar association of zircon ages was found within the xenocrystic cores in the studied volcanic rocks. The presented detrital and xenocrystic zircon ages specify the provenance of the Tribeč Permian deposits from the Western Carpathian Crystalline Basement crust, characteristic of derivation from the Variscan magmatic rocks and reworked fragments of Cadomian crust.