International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Volume 67 no. 2 / April 2016

Volume 67 no. 2 / April 2016

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Articles in this issue

  • The Schwarzhorn Amphibolite (Eastern Rätikon, Austria): an Early Cambrian intrusion in the Lower Austroalpine basement

    Abstract: The Alpine nappe stack in the Penninic-Austroalpine boundary zone in the Rätikon (Austria) contains a 4×1 km tectonic sliver of meta-diorite, known as the Schwarzhorn Amphibolite. It was deformed and metamorphosed in the amphibolite facies and is unconformably overlain by unmetamorphic Lower Triassic sandstone, indicating pre-Triassic metamorphism. Cataclastic deformation and brecciation of the amphibolite is related to normal faulting and block tilting during Jurassic rifting. Zircon dating of the Schwarzhorn Amphibolite using LA-ICP-MS gave a U-Pb age of 529+9/–8 Ma, interpreted as the crystallization age of the protolith. Geochemical characteristics indicate formation of the magmatic protolith in a supra-subduction zone setting. The Cambrian protolith age identifies the Schwarzhorn Amphibolite as a pre-Variscan element within the Austroalpine basement. Similar calc-alkaline igneous rocks of Late Neoproterozoic to Early Cambrian age are found in the Upper Austroalpine Silvretta Nappe nearby and in several other Variscan basement units of the Alps, interpreted to have formed in a peri-Gondwanan active-margin or island-arc setting.
  • Perovskite, reaction product of a harzburgite with Jurassic–Cretaceous accretionary wedge fluids (Western Carpathians, Slovakia): evidence from the whole-rock and mineral trace element data

    Abstract: Perovskite (Prv) was discovered in an abyssal harzburgite from a “mélange” type blueschist-bearing accretionary wedge of the Western Carpathians (Meliata Unit, Slovakia). Perovskite-1 formation in serpentinized orthopyroxene may be simplified by the mass-balance reaction: Ca2Si2O6 (Ca-pyroxene-member)+2Fe2TiO4 (ulvöspinel molecule in spinel)+2H2O+O2=2CaTiO3 (Prv)+2SiO2+4FeOOH (goethite). Perovskite-2 occurs in a chlorite-rich blackwall zone separating serpentinite and rodingite veins, and in rodingite veins alone. The bulk-rock trace-element patterns suggest negligible differences from visually and microscopically less (“core”) to strongly serpentinized harzburgite due to serpentinization and rodingitization: an enrichment in LREE(La,Ce), Cs, ±Ba, U, Nb, Pb, As, Sb, ±Nd and Li in comparison with HREE, Rb and Sr. The U/Pb perovskite ages at ~135 Ma are interpreted to record the interaction of metamorphic fluids with harzburgite blocks in the Neotethyan Meliatic accretionary wedge. Our LA–ICP–MS mineral study provides a complex view on trace element behaviour during the two stages of rodingitization connected with Prv genesis. The positive anomalies of Cs, U, Ta, Pb, As, Sb, Pr and Nd in Cpx, Opx and Ol are combined with the negative anomalies of Rb, Ba, Th, Nb and Sr in these minerals. The similar positive anomalies of Cs, U, Ta, ±Be, As, Sb found in typical serpentinization and rodingitization minerals, with variable contents of La, Ce and Nd, and negative anomalies of Rb, Ba, Th, Nb and Sr suggest involvement of crustal fluids during MP-LP/LT accretionary wedge metamorphism. LA–ICP–MS study revealed strong depletion in LREE from Prv-1 to Prv-2, and a typically negative Eu (and Ti) anomaly for Prv-1, while a positive Eu (and Ti) anomaly for Prv-2. Our multi-element diagram depicts enrichment in U, Nb, La, Ce, As, Sb, Pr, Nd and decreased Rb, Ba, Th, Ta, Pb, Sr, Zr in both Prv generations. In general, both Prv generations are very close to the end-member composition. In spite of low concentrations of isomorphic constituents, Prv-1 and Prv-2 display the A(La,Ce)3+ + B(Fe,Cr)3+ = ACa2+ + BTi4+ heterovalent couple substitution. A decrease of ferric iron in Prv-2 indicates increasing reduction conditions during rodingitization.
  • The Upper Cretaceous Ostravice Sandstone in the Polish sector of the Silesian Nappe, Outer Western Carpathians

    Abstract: The Ostravice Sandstone Member was identified and described as a lithostratigraphic unit in the Polish part of the Outer Carpathians. This division occurs in the lowermost part of the Godula Formation, is underlain by variegated deposits of the Mazák Formation or directly by the Barnasiówka and Lhoty formations, and overlain by the Czernichów Member of the Godula Formation. Domination by thick- and very thick-bedded sandstones, conglomeratic sandstones and conglomerates rich in calcareous clasts, mostly of the Štramberk-type limestones, is typical for the Ostravice Sandstone Member. These deposits are widespread between the Moravskoslezské Beskydy Mountains in the Czech Republic and the Ciężkowice Foothills in Poland. The documentation of the Ostravice Sandstone Member occurrence as well as the petrological, sedimentological features, and inventory of the carbonate clasts are presented here.
  • Euryhaline preferences of the decapod crab Mioplax socialis enabled it to survive during the Badenian/Sarmatian extinction (Miocene) in the Central Paratethys

    Abstract: Although decapod crustaceans of the Central Paratethys were diverse during the Badenian (Langhian–Early Serravallian), a dramatic drop in their diversity occurred at the boundary with the Sarmatian. A crab Mioplax socialis is one of the few decapods reported from the Lower Sarmatian (Mohrensternia Zone) of the Paratethys. Until now, this species has been known from only a handful of specimens from Austria, Croatia and Bulgaria (Central Paratethys), and its systematics and ecology remain poorly known. Here, on the basis of new specimens from the Sarmatian tuffitic clays of the Stretava Formation (Skároš, Eastern Slovakia) we confirm that this species belongs to the subfamily Chasmocarcininae. The diagnostic characters of the male sternum that allow this classification are reported for the first time. The molluscan assemblage co-occurring with M. socialis demonstrate that this species tolerated conditions with variable salinity. Its tolerance of a broad range of salinity regimes may thus explain its survival across the Badenian–Sarmatian extinction event. Preservation of near-complete and fully articulated individuals of M. socialis suggests calm conditions and short residence times on the sediment-water interface.
  • Structural evolution of the Turňa Unit constrained by fold and cleavage analyses and its consequences for the regional tectonic models of the Western Carpathians

    Abstract: The Turňa Unit (Turnaicum, Tornaicum) is one of the three nappe systems involved in the geological structure of the inner zones of the Western Carpathians. The unit is formed by a system of partial nappes and duplexes, which overlie the Meliata Unit s.l. and are overridden by the Silica Nappe. The Slovenská skala partial nappe in the investigated area includes clastic sediments of the mid-Carboniferous, Permian and Early Triassic age, followed by mostly deep-water Middle–Upper Triassic succession predominantly composed of carbonates. Structural analysis of cleavage planes and folds was carried out predominantly in the Lower Triassic Werfen Formation. The measured deformational structures are polygenetic and were principally formed in three successive deformation stages. The first deformation stage is represented by bedding-parallel, very low-grade metamorphic foliation that was related to nappe stacking and formation of the Mesozoic accretionary wedge during the latest Jurassic and earliest Cretaceous. The second deformation stage is represented by systems of open to closed, partly asymmetric folds with SW–NE oriented, steeply NW- or SE-dipping axial-plane cleavage. Regionally, the folded bedding planes are usually moderately SE-ward dipping, the NW-ward and subvertical dips are less common. The mesoscopic fold structures predominantly occur in the SW–NE trending anticlinal and synclinal hinge zones of large-scale folds. These structures evolved in a compressional tectonic regime with the NW–SE to N–S orientation of the maximum compressional axis. The third observed deformation stage was activated during ENE–WSW oriented shortening. This stage is chiefly represented by open, kink-type folds. Some inferences for regional structures and tectonic evolution of the area are discussed as well.
  • Testing of multidimensional tectonomagmatic discrimination diagrams on fresh and altered rocks

    Abstract: We evaluated 55 multidimensional diagrams proposed during 2004–2013 for the tectonic discrimination ofultrabasic, basic, intermediate, and acid magmas. The Miocene to Recent rock samples for testing the diagrams had notbeen used for constructing them. Eighteen test studies (2 from ocean island; 2 from ocean island/continental rift; 6 fromcontinental rift; 4 from continental arc; 2 from island arc; 1 from mid-ocean ridge, and 1 from collision) of relativelyfresh rocks fully confirmed the satisfactory functioning of these diagrams for all tectonic fields for which they wereproposed. Eight additional case studies on hydrothermally altered or moderately to highly weathered rocks were alsopresented to achieve further understanding of the functioning of these diagrams. For these rocks as well, the diagramsindicated the expected tectonic setting. We also show that for testing or using these diagrams the freely-available geochemistry databases should be used with caution but certainly after ascertaining the correct magma types to selectthe appropriate diagram sets. The results encourage us to recommend these diagrams for deciphering the tectonic settingof older terranes or areas with complex or transitional tectonic settings.