Granitic pegmatites of the beryl–columbite subtype in the Tatric Superunit, Western Carpathians, Slovakia: Variscan age determination by in-situ LA–ICP–MS U–Pb dating of columbite-group minerals
Abstract: Accessory columbite-(Fe) to tantalite-(Fe) from three granitic pegmatites of the Tatric Superunit (Bratislava Massif of the Malé Karpaty Mts., Bojná Massif of the Považský Inovec Mts. and Suchý Massif of the Strážovské Mts.) was used for dating by the in-situ LA–ICP–MS U–Pb method. The columbite–tantalite crystals were sampled from the most fractionated pegmatite dykes of the beryl–columbite subtype situated in the pre-Alpine, Paleozoic crystalline basement of the Tatric Superunit, Western Carpathians (western and central Slovakia). The obtained columbite–tantalite Concordia ages are as follows: 354.5 ± 4.5 Ma (Jezuitské Lesy pegmatite, the Bratislava granite Massif), 360 ± 5.0 Ma (Moravany nad Váhom, Striebornica Ridge pegmatite, the Bojná Massif), and 352 ± 8.5 Ma (Liešťany, Bystrý Hill pegmatite, the Suchý Massif). The columbite–tantalite ages show Mid-Variscan formation of rare-element pegmatites from the Devonian/Carboniferous boundary to Tournaisian stage, which is coeval with the emplacement of cogenetic granites during the main phase of Variscan intracontinental subduction and collision. The obtained columbite–tantalite age interval of rare-element granitic pegmatites of the Tatric Superunit (~360 to 350 Ma) is generally older than the ages of Be- and Li-rich rare-element pegmatites of the Moldanubian Superunit in the Bohemian Massif (~340 to 320 Ma). The rare-element granitic pegmatites of the Austroalpine Superunit (Eastern Alps) are significantly younger (~290 to 240 Ma) because they were formed in an extension regime during the Permian to Early Triassic post-Variscan orogenic collapse.
Provenance of Upper Paleozoic Sandstones from the Western Carpathians (Slovakia): Petrofacies analysis and U–Pb detrital zircon geochronology
Abstract: The provenance of Upper Paleozoic sediments in the Western Carpathians was derived by a petrofacies analysis of sandstones, including the U–Pb geochronology of detrital zircons. The Upper Paleozoic sedimentary basins were formed sequentially by tectonic processes associated with the Variscan continental collision, as well as by subsequent transpressional/transtensional and extensional regimes. Fore-arc related and proforeland basins were formed in the Late Tournaisian/Visean and subsequently in the Bashkirian/Moscovian. Transpressional/transtensional and extensional basins were formed successively on both sides of the continental collisional suture, both in the proforeland and retroforeland parts in the Late Pennsylvanian and later in the Cisuralian and Guadalupian. The sandstone petrofacies, as well as the detrital zircon distribution, indicate source areas directly from the underlying crystalline basement: a magmatic arc, an uplifted continental block for the Central Western Carpathian basins, and a recycled orogen for the Inner Western Carpathian basins. Detrital zircon age spectra record distinct stages of protracted Ediacaran to Carboniferous tectonosedimentary processes. This indicates a different palinspastic position of source areas along the peri-Gonwanan realm, the West African Craton, and the Sahara Metacraton in the Neoproterozoic.
Lithospheric scale cross-section through the Transylvanian Basin: A joint geophysical and geological survey
Abstract: The transition area between the Pannonian Basin and the East Carpathians is the subject of considerable tectonic research in Central Europe because of its geological diversity, especially for Lithosphere–Asthenosphere Boundary determinations. The major objective of this study is to investigate the Earth’s lithospheric structure and in particular to determine the Lithosphere–Asthenosphere Boundary from the Pannonian Basin, through the Transylvanian Basin to the Carpathian Bend area. We recorded six new deep magnetotelluric soundings and used two archive measurements to complete the information and to put additional constraints on the depth of the Lithosphere–Asthenosphere Boundary. In the part of the discussions we provide a brief overview of the existing various methodologies and Lithosphere–Asthenosphere Boundary determinations for the wider Carpathian–Pannonian region and Europe and comparison with new magnetotelluric results. The lowest Lithosphere–Asthenosphere Boundary depth was detected in the Pannonian Basin (~50 km). Our results indicate in addition that the Lithosphere-Asthenosphere Boundary beneath the Transylvanian Basin (~70–80 km) is not thick and much thinner than those of the European and Moesian Platforms. The additional geophysical information (geomagnetic data and phase tensor results) detected the presence of deep well conductive zones towards the Pannonian Basin, the Bogdan Vodă–Dragoș Vodă fault and the East Carpathians. This could be explained by the elevated position of the well conductive asthenosphere in the Pannonian Basin and deep and presumably fluid rich tectonic zones associated with the Bogdan Vodă–Dragoș Vodă fault and the East Carpathians. The phase tensors highlighted that the most complex tectonic zones are present in the vicinity of the East Carpathians (where the average Lithosphere–Asthenosphere Boundary depth is >100 km), which is in line with the relatively young age of the mountain belt and the very complex nature of collisional orogens.
Exhumation history of the Juhor Mts. in Central Serbia, the Northern Serbo–Macedonian Subunit
Abstract: In this study, we combined low-t thermochronology with outcrop- to micro-scale kinematic and petrological observations in the metamorphic basement of the Juhor Mts. in Central Serbia. The Juhor Mts. comprise northern parts of the Europe-derived Serbo–Macedonian Unit, at the transition towards the Adria-derived tectonic units of the Internal Dinarides. The Late Paleozoic Variscan orogeny resulted in the medium-grade greenschist to amphibolite facies metamorphism in the core of the mountains, as inferred from our thin section-scale observations. During the subsequent Alpine orogeny, the tectonic setting of the entire Europe–Adria transitional area was strongly influenced by the geodynamic evolution of the intervening Neotethyan Vardar Ocean. The last recorded thermal overprint in the northern segments of the Serbo–Macedonian metamorphics occurred in the latest Jurassic due to their burial during the obduction of the Eastern Vardar ophiolites over the European continental margin. According to our thermochronological and field structural data, the exhumation of the Juhor Mts. metamorphic basement occurred during two separate phases of extensional deformations. During the Late Cretaceous extension, the Serbo–Macedonian metamorphics were exhumed for ~3 to 6 km along a ductile Morava shear zone, and later structurally juxtaposed against the low-grade metamorphics of the adjacent Supragetic Unit of the Serbian Carpathians. The latest phase of ~1 to 2,5 km tectonic exhumation and uplift in the Miocene took place along the brittle normal faults that accommodated the opening of the Morava Valley Corridor, which forms the southern prolongation of the Pannonian Basin. It is plausible, therefore, that these Miocene normal faults are reactivated segments of thrusts inherited from the preceding Paleogene phase of the Adria–Europe collision.
