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More evidence on Neoproterozoic terranes in Southern Poland and southeastern Romania

Żelaźniewicz A., Buła Z., Fanning M., Seghedi A., Żaba J.

Geological Quarterly

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2009

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Vol. 53, No 1

93-124

EN

New geological, geochemical and U-Pb SHRIMP zircon age data brought more information about basement units in subsurface of Southern Poland and SE Romania, which allows to revise and refine some earlier models in the framework of the break-up of the Rodinia/Pannotia supercontinent. In the Brno Block, Moravia, and in the Upper Silesia Block, three different terranes formed the composite Brunovistulia Terrane. The Thaya Terrane (low eNd(T)) of Gondwana (Amazonia) descent collided obliquely at 640–620 Ma with the Slavkov Terrane (moderate eNd(T)) composed of amphibolite facies metasediments and arc-related, mostly unfoliated granitoids which intruded at 580–560 Ma. At that time, back-arc rifting separated the couple Thaya–Slavkov (inherited zircons: 1.01–1.2, 1.4–1.5, 1.65–1.8 Ga) that drifted away from Gondwana until collision around 560–550 Ma with the Rzeszotary Terrane, the Palaeoproterozoic (2.7–2.0 Ga) crustal sliver derived from Amazonia or West Africa. At least these three units composed Brunovistulia, which occurred at low latitudes in proximity to Baltica as shown by palaeomagnetic and palaeobiogeographic data. Then Brunovistulia was accreted to the thinned passive margin of Baltica around its Małopolska promontory/proximal terrane. A complex foreland flysch basin developed in front of the Slavkov–Rzeszotary suture and across the Rzeszotary–Baltica/Małopolska border. The further from the suture the less amount of the 640–550 Ma detrital zircons extracted from the Thaya–Slavkov hinterland and the smaller eNd(T) values. In West Małopolska, the flysch contains mainly Neoproterozoic zircons (720–550 Ma), whereas in East Małopolska 1.8–2.1 Ga and 2.5 Ga zircons dominate, which resembles nearby Baltica. The basin infill was multiphase folded and sheared; in Up per Silesia prior to deposition of the pre-Holmia Cambrian over step. In Małopolska, the folded flysch series formed a large-scale antiformal stack with thermal anticline in its core marked by low-grade metamorphic overprint. In Central Dobrogea, Moesia, Ediacaran flysch also contains mainly 700–575 Ma detrital zircons which link the source area, likely in South Dobrogea with ca. 560 Ma granitoids, rather close with Gondwana. However, fauna in Lower Cambrian overstep strata shows Baltican affinity. Such features resemble Upper Silesia, thus Brunovistulia might have extended beneath the Carpathians down to Moesia. The other part of South Dobrogea with Palaeoproterozoic ironstones resembles Ukrainian banded iron formation. If true, the Baltican sliver would be incorporated in Moesia. Such a possibility concurs with the provenance data from Ediacaran flysch of Central Dobrogea, which points to uplifted continental block as a source of derital material. Our study supports an earlier proposition that at the end of the Neoproterozoic a group of small terranes that included Brunovistulia, Moesia and Małopolska formed the Teisseyre-Tornquist Terrane As semblage (TTA). In our model, a characterisistic feature of the TTA was a mixture of crustal elements that were derived from both Gondwana and Baltica, which gave rise to mutual collisions of the elements prior to and concurrent with the docking to Baltica in latest Ediacaran times. The presence of extensive younger covers and complex Phanerozoic evolution of individual members of the TTA impede the recognition of their Neoproterozoic history.

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Evolution of the Mesozoic basins on the southwestern edge of the East European Craton (Poland, Ukraine, Moldova, Romania)

Świdrowska J., Hakenberg M., Poluhtovič B., Seghedi A., Višnâkov I.

Studia Geologica Polonica

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2008

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Vol. 130

3-130

EN

The sedimentary cover of the SW margin of the East European Craton (EEC) records its Mesozoic evolution from Permian to Early Maastrichtian time. Structural units of the Mid-Polish Swell with bounding synclines, the Stryi Depression, the Moldavian Platform, the Pre-Dobrogea Depression (PDD) and the North Dobrogea (ND) are groupped along the Teisseyre-Tornquist Zone (TTZ), one of the most important lineaments of the European Plate. They developed above the Trans-European Suture Zone (TESZ), the contact zone of Precambrian and Palaeozoic domains of crustal consolidation. The investigated area forms a belt 1000 km long that strikes across four states down to the Black Sea. The stratigraphy and facies data based on the profiles from many hundreds of wells and outcrops are summarized on thickness and lithofacies maps covering 16 time-spans. They show palaeogeogra- phic history of sedimentary basins of the SE part of Mid-Polish Trough (MPT), the Stryi Depression and the Pre-Dobrogea Depression. Fragmentary record of epicontinental sediments in the ND could be interpreted referring to depositional history of the PDD. The facies-thickness maps were transfor- med to maps of accumulation rate reflecting subsidence rates. Sedimentary and structural evolution of the two outermost basins, MPT and PDD, give evidences for their genetic independence and the lack of their direct connections along direction of TTZ till the end of Jurassic time. The Triassic-Middle Jurassic evolution of the North Dobrogea suggests that it could lie farther to the SW in the Tethyan realm. Deep-water sequences of the ND did not display any relation to the epiplatform sediments in the PDD up to the Bathonian. Mid-Cimmerian transpressional docking of the ND block to the PDD gave the beginning of their common epicontinental Jurassic history with subsidence axis striking W-E. Geometric junction of both external basins (MPT and PDD) in NW-SE direction occurred during the Early Cretaceous as a result of origin of foredeep basin located to the north of the ND inverted block, together with the western part of the PDD. Inversion was a consequence of the Neo-Cimmerian collision in the Northern Tethys and docking of the Central Dobrogea to the ND. The evolution of the PDD was connected with the eastern Mediterranean realm from Albian time on. A multiphase (10 stages) tectonic history of the Mid-Polish Trough and the Stryi Depression was recognized. Clockwise rotation of the two principal stress axes in horizontal plane controlled basin opening. A change of the strike-slip component along the TTZ direction and over the TESZ occurred from sinistral (Early Jurassic), through the lack of horizontal displacements in Albian-Cenomanian time, to dextral component from the Turonian till the end of Cretaceous. During the inversion the s1 axis reached a NE-SW orientation.

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The Romanian Carpathian Foreland

Seghedi A.

Reports on Geodesy

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1998

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z. 7/37

21-48