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Magna T.,University of Lausanne | Magna T.,University of Munster | Magna T.,Czech Geological Survey | Janousek V.,Czech Geological Survey | And 4 more authors.
Chemical Geology | Year: 2010

Lithium (Li) elemental and isotope data are presented for a suite of plutonic rocks (I-, S-, A- and SS-type, coexisting mafic bodies) from the Western Carpathians, Slovakia, that were generated throughout the complete Variscan orogenic cycle. I-type granites show a limited range of δ7Li, contrasting with the large variations found in S-type granites and orthogneisses of distinct ages. This contradicts previous reports of predominantly light-Li S-type granites, sourcing metasedimentary lithologies, and isotopically heavier I-type granites, derived from meta-igneous sources. An almost exclusively heavy Li isotope signature (δ7Li >4.7‰) found in four out of five A-type granites rules out several commonly accepted petrogenetic scenarios such as remelting of granulitic residue after formation of I-type granitic melts, anatexis of calc-alkaline meta-igneous crust or extensive closed-system fractional crystallization of mantle-derived magmas. Instead, it most probably reflects a derivation of A-type granites from a mantle wedge modified by slab-derived fluids during an Early Variscan or Pan-African subduction episode. In contrast, the distinct and lower δ7Li values (<1.2‰) in the contemporaneous SS-type granites can be related to their likely pelitic parentage.Mafic rocks (gabbros and diorites), associated with several occurrences of granites, are uniformly Li-rich and isotopically light (<-0.5‰), precluding a direct derivation from the mantle. These signatures testify to their cumulate origin whereby kinetic effects may be a viable explanation for the light Li isotope compositions, associated with diffusive redistribution of Li between mantle-derived mafic melts and acid magmas. This corroborates recent studies on faster diffusion of 6Li compared with 7Li in natural systems.Taken together, the presumed dichotomy between the sources and processes leading to generation of S- and I-type granitic magmas does not seem to be reflected by Li isotope signatures in a simple and globally valid manner. Interpretation of Li isotope compositions thus needs to be paralleled by other available information on petrology, whole-rock geochemistry and the magmatic context. © 2010 Elsevier B.V.

Kohut M.,Dionyz Stur State Institute of Geology | Trubac J.,Czech Geological Survey | Novotny L.,Nova Energy | Ackerman L.,Czech Geological Survey | And 4 more authors.
Journal of Geosciences (Czech Republic) | Year: 2013

The Kurišková U-Mo deposit from the Gemeric Unit of the Western Carpathians (Slovakia) is an example of polygenic deposit whose origin involved several events: endogenous, related to magmatism/volcanism, and exogenous, associated with precipitation from meteoric hydrothermal fluids in repeated tectonically-driven (fold & thrust and shear zones) channel ways penetrating the Permian Huta volcano-sedimentary complex. Sources of the U-Mo mineralization were multiple: (a) molybdenite was derived directly from juvenile hydrothermal fluids related to igneous activity, (b)the U mineralization formed from meteoric fluids circulating through altered and metamorphosed basaltic and rhyolitic volcanics intercalated by clastic sediments (sandstones and mudrocks), which interacted in an arid to humid climate with organic and carbonate substances within Permian basin. The principal ore-forming minerals are uraninite, coffinite, molybdenite and apatite with rare orthobrannerite and powellite. Two basic mineralization forms are present: (a)tabular - "stratiform like" and (b) stockwork intraformational and/or dislocation stockworks in shear zones. The Re-Os molybdenite dating confirmed crystallization from igneous source in Late Permian (Lopingian; 257.2 ± 3.0 Ma to 255.6 ± 3.7 Ma) for massive vein mineralization, whereas the superimposed U remobilization within shear zones occurred in the Triassic/Jurassic period. The Kurišková U-Mo deposit represents a polygenic endo/exogenous hydrothermal deposit of the Permian/Paleo-Alpine age, with metals sourced in Permian volcanosedimentary rocks that were leached by shear zone-related meteoric fluids.

Uher P.,Comenius University | Kohut M.,Dionyz Stur State Institute of Geology | Ondrejka M.,Comenius University | Konecny P.,Dionyz Stur State Institute of Geology | Siman P.,Slovak Academy of Sciences
Acta Geologica Slovaca | Year: 2014

Monazite-(Ce) represents a characteristic magmatic accessory mineral of the Hercynian peraluminous S-type granites to granodiorites and related granitic pegmatites of the Bratislava Granitic Massif (BGM), Malé Karpaty Mountains, Central Western Carpathians, SW Slovakia. Monazite forms euhedral to subhedral crystals, up to 200 μm in size, usually it is unzoned in BSE, rarely it reveals oscillatory or sector zoning. Thorium concentrations of 2 to 9 wt. % ThO2 (≤ 0.09 apfu) and local elevated uranium contents (≤ 4.3 wt. % UO2, ≤ 0.04 apfu) are characteristic for the pegmatite monazites. Both huttonite ThSiREE-1P-1 and cheralite Ca(Th,U)REE-2 substitutions took place in the studied monazite. Electron-microprobe Th-U-Pb monazite dating of the granites and pegmatites gave an isochron age of 353 ± 2 Ma (MSWD = 0.88, n = 290), which confirmed the meso-Hercynian, Lower Carboniferous (Mississipian) magmatic crystallization. An analogous age (359 ± 11 Ma) was obtained from monazite from adjacent paragneiss, corresponding to the age of the Hercynian contact thermal metamorphism related to the granite intrusion of BGM. Monazite in some granite shows also older clastic or authigenic grains or zones (∼ 505 to 400 Ma, with maximum of 420 ± 7 Ma) which probably represents inherited material from the Lower Paleozoic metapelitic to metapsammitic protolith of BGM.

Vojtko R.,Comenius University | Marko F.,Comenius University | Preusser F.,University of Stockholm | Madaras J.,Dionyz Stur State Institute of Geology | And 2 more authors.
Geologica Carpathica | Year: 2011

The Cenozoic structure of the Western Carpathians is strongly controlled by faults. The E-W striking Vikartovce fault is one of the most distinctive dislocations in the region, evident by its geological structure and terrain morphology. This feature has been assumed to be a Quaternary reactivated fault according to many attributes such as its perfect linearity, faceted slopes, the distribution of travertines along the fault, and also its apparent prominent influence on the drainage network. The neotectonic character of the fault is documented herein by morphotectonic studies, longitudinal and transverse valley profile analyses, terrace system analysis, and mountain front sinuosity. Late Pleistocene activity of the Vikartovce fault is now proven by luminescence dating of fault-cut and uplifted alluvial sediments, presently located on the crest of the tilted block. These sediments must slightly pre-date the age of river redirection. Considering the results of both luminescence dating and palynological analyses, the change of river course probably occurred during the final phase of the Riss Glaciation (135 ± 14 ka). The normal displacement along the fault during the Late Quaternary has been estimated to about 105-135 m, resulting in an average slip rate of at least 0.8-1.0 mm • yr -1. The present results identify the Vikartovce fault as one of the youngest active faults in the Central Western Carpathians.

Danisik M.,Curtin University Australia | Danisik M.,University of Waikato | Kadlec J.,Academy of Sciences of the Czech Republic | Glotzbach C.,Leibniz University of Hanover | And 8 more authors.
Swiss Journal of Geosciences | Year: 2011

A combination of four thermochronometers [zircon fission track (ZFT), zircon (U-Th)/He (ZHe), apatite fission track (AFT) and apatite (U-Th-[Sm])/He (AHe) dating methods] applied to a valley to ridge transect is used to resolve the issues of metamorphic, exhumation and topographic evolution of the Nízke Tatry Mts. in the Western Carpathians. The ZFT ages of 132. 1 ± 8.3,155.1 ± 12.9, 146.8 ± 8.6 and 144.9 ± 11.0 Ma show that Variscan crystalline basement of the Nízke Tatry Mts. was heated to temperatures &210°C during the Mesozoic and experienced a low-grade Alpine metamorphic overprint. ZHe and AFT ages, clustering at ~55-40 and ~45-40 Ma, respectively, revealed a rapid Eocene cooling event, documenting erosional and/or tectonic exhumation related to the collapse of the Carpathian orogenic wedge. This is the first evidence that exhumation of crystalline cores in the Western Carpathians took place in the Eocene and not in the Cretaceous as traditionally believed. Bimodal AFT length distributions, Early Miocene AHe ages and thermal modelling results suggest that the samples were heated to temperatures of ~55-90°C during Oligocene-Miocene times. This thermal event may be related either to the Oligocene/Miocene sedimentary burial, or Miocene magmatic activity and increased heat flow. This finding supports the concept of thermal instability of the Carpathian crystalline bodies during the post-Eocene period. © 2011 Swiss Geological Society.

Danisik M.,Curtin University Australia | Danisik M.,University of Tübingen | Kohut M.,Dionyz Stur State Institute of Geology | Broska I.,Slovak Academy of Sciences | Frisch W.,University of Tübingen
Geologica Carpathica | Year: 2010

We apply zircon and apatite fission track thermochronology (ZFT and AFT, respectively) to the Variscan crystal-line basement of the Malá Fatra Mts (Central Western Carpathians) in order to constrain the thermal history. The samples yielded three Early Cretaceous ZFT ages (143.7±9.6, 143.7±8.3, 135.3±6.9 Ma) and one Eocene age (45.2±2.1 Ma), proving that the basement was affected by a very low-grade Alpine metamorphic overprint. Although the precise timing and mechanisms of the overprint cannot be unequivocally resolved, we propose and discuss three alternative explanations: (i) a Jurassic/Cretaceous thermal event related to elevated heat flow associated with extensional tectonics, (ii) early Late Cretaceous thrusting and/or (iii) an Eocene orogeny. Thermal modelling of the AFT cooling ages (13.8±1.4 to 9.6±0.6 Ma) revealed fast cooling through the apatite partial annealing zone. The cooling is interpreted in terms of exhumation of the basement and creation of topographic relief, as corroborated by the sedimentary record in the surrounding Neogene depressions. Our AFT results significantly refine a general exhumation pattern of basement complexes in the Central Western Carpathians. A younging of AFT ages towards the orogenic front is evident, where all the external massifs located closest to the orogenic front (including Malá Fatra Mts) were exhumed after ∼13 Ma from temperatures above ∼120 °C.

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