Anna Vozárová

Late Variscan (Carboniferous to Permian) environments in the Circum Pannonian Region

Late Variscan (Carboniferous to Permian) environments in the Circum Pannonian Region The Pennsylvanian-Cisuralian late-orogenic and post-orogenic paleoenvironments of the Circum Pannonian Region (CPR) include tectono-stratigraphic sequences developed from the Upper Bashkirian-Moscovian marine early molasse stage up to the Guadalupian-Lopingian post-orogenic stage, with gradual connection to the beginning of the Alpine (Neotethyan) sedimentary cycle. Shallow marine siliciclastic or carbonate siliciclastic overstep sequences started in the internal part of the Variscan orogenic belt during the latest Serpukhovian and Bashkirian-Moscovian. They overlapped unconformably the variably metamorphosed Variscan basement, or weakly deformed and metamorphosed foreland and syn-orogenic flysch sediments of Mississippian to Early Pennsylvanian age. The post-Variscan rifting largely affected the Variscan orogenic belt by reactivation of the Variscan lithosphere. The late- to post-orogenic terrestrial sequences started within the internal part of the Variscan orogenic belt during the Middle/Late Pennsylvanian. It continued gradually to terrestrial-shallow water carbonate-siliciclastic sequences in its external part through the Permian. According to the present configuration, the Alpine (Neotethyan) northward shifting transgression started during the Guadalupian/Lopingian in the South and during the Early Triassic in the North.

Geochemistry of the Permian sandstones from the Malužiná Formation in the Malé Karpaty Mts (Hronic Unit, Western Carpathians, Slovakia): implications for source-area weathering, provenance and tectonic setting

Abstract The Permian sandstones of the Malužiná Formation in the northern part of the Malé Karpaty Mts are dominantly quartzofeldspathic and quartzolithic in composition with abundant feldspars and volcanic, plutonic igneous and less metasedimentary lithic fragments, indicating the sand grains were derived from a basement uplift and recycled orogen. The Malužiná Formation sandstones have moderate to high SiO2 contents (68-85 wt. %; on average 76 wt. %), TiO2 concentrations averaging 0.3 wt. %, Al2O3 contents of about 12 wt. %, and Fe2O3 (total Fe as Fe2O3) + MgO contents of around 2.9 wt. %. The Chemical Index of Alteration (CIA) values for the Permian Malužiná Formation sandstones vary from 45 to 68 with an average of 55, indicating low to moderate weathering of the source area. The bulk chemical composition and selected trace elements preserve the signatures of a felsic and intermediate igneous provenance, and suggest mostly an active continental margin tectonic setting of the source area for the Malužiná Formation sandstones. The Eu/Eu* (~0.78), La/Sc (~7.28), Th/Sc (~2.10), La/Co (~6.67), Th/Co (~1.85), and Cr/Th (~6.57) ratios as well as the chondrite-normalized REE patterns with flat HREE, LREE enrichment, and negative Eu anomalies indicate derivation of the Malužiná Formation sandstones from felsic rock sources. The deposition of the Malužiná Formation sandstones took place in a rifted continental margin environment supplied from collision orogen on a thick continental crust composed of rocks of older fold belts.

Permian single crystal U-Pb zircon age of the Rožňava Formation volcanites (Southern Gemeric Unit, Western Carpathians, Slovakia)

Permian single crystal U-Pb zircon age of the Rožňava Formation volcanites (Southern Gemeric Unit, Western Carpathians, Slovakia) Zircon populations from the Rožňava Formation volcanic rock complex have been analysed. Euhedral zircons from the 1st volcanogenic horizon with fine oscillatory growth zoning, typical of magmatic origin, gave the average concordia age of 273.3 ± 2.8 Ma, with Th/U ratios in the range of 0.44-0.73. The Permian ages ranging from 266 to 284 Ma were identified in the wider, zoned or unzoned, central zircon parts, as well as in their fine-zoned oscillatory rims. The average concordia age of 275.3 ± 2.9 was obtained from the euhedral zircon population of the 2nd volcanogenic horizon of the Rožňava Formation. The analyses were performed on zoned magmatic zircons in the age interval from 267 to 287 Ma, with Th/U ratios in the range of 0.39-0.75. In the later zircon population two inherited zircon grains were dated giving the age of 842 ± 12 Ma (Neoproterozoic) and 456 ± 7 Ma (Late Ordovician). The magmatic zircon ages document the Kungurian age of Permian volcanic activity and contemporaneous establishment of the south-Gemeric basin. The time span of volcanic activity corresponds to the collapse of the Western Carpathian Variscan foreland which expanded southward.

Permian volcanics in the Northern Gemericum and Bôrka Nappe system: U-Pb zircon dating and the implications for geodynamic evolution (Western Carpathians, Slovakia)

Permian volcanics in the Northern Gemericum and Bôrka Nappe system: U-Pb zircon dating and the implications for geodynamic evolution (Western Carpathians, Slovakia) U-Pb dating (SHRIMP) of magmatic zircon ages from the Northern Gemericum Permian volcanics (Petrová Hora Formation) yielded the Concordia age of 272.4 ± 7.3 Ma for basaltic andesite, as well as the Concordia age of 275.2 ± 4 Ma for rhyodacites. Both zircon ages correspond to the Cisuralian Epoch in the time span of the Kungurian Stage. Acquired 206Pb/238U zircon age data support the nearly contemporaneous origin of the acid and basic volcanogenic members in the Northern Gemericum Permian strata. The bimodal volcanic suite proves the transtension/extension tectonic regime in the North Gemeric sedimentary basin during the Late Cisuralian. The magmatic zircon ages of rhyodacites, occurring in the lower thrust sheet of the Bôrka Nappe (Jasov Formation), gave a younger Concordia age of 266 ± 1.8 Ma proving the Guadalupian Epoch, in the time span of the Wordian/Capitanian. In comparison to the Northern Gemericum realm, this age refers to the relatively younger stage of rift-related extensional movements. In the wide Alpine-Dinarides realm the Middle Permian (Guadalupian) movements are related to the beginning of the Alpine sedimentary cycle. Thus, the Middle Permian rifting expresses the beginning of the formation of the future Meliata oceanic trough.

Geochemistry and Sr, Nd isotopic composition of the Hronic Upper Paleozoic basic rocks (Western Carpathians, Slovakia)

Abstract The paper presents new major and trace element and first Sr-Nd isotope data from selected lavas among the Permian basaltic andesite and basalts of the Hronicum Unit and the dolerite dykes cutting mainly the Pennsylvanian strata. The basic rocks are characterized by small to moderate mg# numbers (30 to 54) and high SiO2 contents (51-57 wt. %). Low values of TiO2 (1.07-1.76 wt. %) span the low-Ti basalts. Ti/Y ratios in the dolerite dykes as well as the basaltic andesite and basalt of the 1st eruption phase are close to the recommended boundary 500 between high-Ti and low-Ti basalts. Ti/Y value from the 2nd eruption phase basalt is higher and inclined to the high-Ti basalts. In spite of this fact, in all studied Hronicum basic rocks Fe2O3* is lower than 12 wt. % and Nb/La ratios (0.3-0.6) are low, which is more characteristic of low-Ti basalts. The basic rocks are characterized by Nb/La ratios (0.56 to 0.33), and negative correlations between Nb/La and SiO2, which point to crustal assimilation and fraction crystallization. The intercept for Sr evolution lines of the 1st intrusive phase basalt is closest to the expected extrusions age (about 290 Ma) with an initial 87Sr/86Sr ratio of about 0.7054. Small differences in calculated values ISr document a partial Sr isotopic heterogeneity source (0.70435-0.70566), or possible contamination of the original magma by crustal material. For Nd analyses of the three samples, the calculated values εCHUR (285 Ma) are positive (from 1.75 to 3.97) for all samples with only subtle variation. Chemical and isotopic data permit us to assume that the parental magma for the Hronicum basic rocks was generated from an enriched heterogeneous source in the subcontinental lithospheric mantle.

Provenance of Permian Malužiná Formation sandstones (Hronicum, Western Carpathians): evidence from monazite geochronology

Abstract The Permian Malužiná Formation and the Pennsylvanian Nižná Boca Formation are Upper Paleozoic volcano- sedimentary complexes in the Hronicum nappe system. Sandstones, shales and conglomerates are the dominant lithological members of the Malužiná Formation sequence. Detrital monazites were analysed by electron microprobe, to obtain Th-U-Pb ages of the source areas. The majority of detrital monazites showed Devonian-Mississippian ages, ranging from 330 to 380 Ma with a weighted average of 351 ± 3.3 (2σ), that correspond well with the main phase of arcrelated magmatic activity in the Western Carpathians. Only a small portion of detrital monazites displayed Permian ages in the range of 250-280 Ma, with a significant maximum around 255 Ma. The weighted average corresponds to 255 ± 6.2 Ma. These monazites may have been partially derived from the synsedimentary acid volcanism that was situated on the margins of the original depositional basin. However, some of the Triassic ages (230-240 Ma), reflect, most likely, the genetic relationship with the overheating connected with Permian and subsequent Triassic extensional regime. Detrital monazite ages document the Variscan age of the source area and also reflect a gradual development of the Hronicum terrestrial rift, accompanied by the heterogeneous cooling of the lithosphere.

First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

Abstract Several magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44–0.27) and for the Nb/U ratio at (9.55–4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new 206U–238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

Late Permian volcanic dykes in the crystalline basement of the Považský Inovec Mts. (Western Carpathians): U–Th–Pb zircon SHRIMP and monazite chemical dating

Abstract This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous) age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U-Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th-U-Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps.

3D density modelling of Gemeric granites of the Western Carpathians

Abstract The position of the Gemeric Superunit within the Western Carpathians is unique due to the occurrence of the Lower Palaeozoic basement rocks together with the autochthonous Upper Palaeozoic cover. The Gemeric granites play one of the most important roles in the framework of the tectonic evolution of this mountain range. They can be observed in several small intrusions outcropping in the western and south-eastern parts of the Gemeric Superunit. Moreover, these granites are particularly interesting in terms of their mineralogy, petrology and ages. The comprehensive geological and geophysical research of the Gemeric granites can help us to better understand structures and tectonic evolution of the Western Carpathians. Therefore, a new and original 3D density model of the Gemeric granites was created by using the interactive geophysical program IGMAS. The results show clearly that the Gemeric granites represent the most significant upper crustal anomalous low-density body in the structure of the Gemeric Superunit. Their average thickness varies in the range of 5–8 km. The upper boundary of the Gemeric granites is much more rugged in comparison with the lower boundary. There are areas, where the granite body outcrops and/or is very close to the surface and places in which its upper boundary is deeper (on average 1 km in the north and 4–5 km in the south). While the depth of the lower boundary varies from 5–7 km in the north to 9–10 km in the south. The northern boundary of the Gemeric granites along the tectonic contact with the Rakovec and Klátov Groups (North Gemeric Units) was interpreted as very steep (almost vertical). The results of the 3D modelling show that the whole structure of the Gemeric Unit, not only the Gemeric granite itself, has an Alpine north-vergent nappe structure. Also, the model suggests that the Silicicum–Turnaicum and Meliaticum nappe units have been overthrusted onto the Golčatov Group.