The Variscan foreland in Poland revisited : new data and new concepts

An earlier concept of the Variscan foreland in Poland (Narkiewicz, 2007) is reconsidered in the light of new stratigraphic, tectonic and geophysical evidence, providing new data on Devonian sedimentation, Carboniferous magmatism and the deep crustal structure of SE Poland. Regional comparisons with the tectonic evolution of Central Europe and the Black Sea region show that the subsidence pattern in the foreland was controlled by alternating phases of accelerated convergence and tectonic standstill along the southern margin of Euramerica. In particular, the Bretonian (Devonian/Carboniferous) compressional deformation resulted from intensified orogenic convergence in the West-Central European Variscides leading to closure of the Saxo-Thuringian Basin and East-Sudetic back-arc basin. Another turning point in the regional tectonosedimentary development around the Mississippian-Pennsylvanian boundary was probably related to the termination of terrane collision in the Black Sea region. Late Pennsylvanian basin inversion was associated with a roughly N-S tectonic shortening. This was partly due to displacement along pre-existing basement discontinuities comprising reactivated Caledonian sutures that also pre-determined the Devonian-Carboniferous basin boundaries. Consequently, deeply-rooted tectonic zones, including the Kraków-Lubliniec and Holy Cross faults and the Teisseyre-Tornquist Zone, focussed maximum compressional and transpressional deformation and associated uplift. Such a concept of terminal Variscan tectonism, termed here the “decoupled model”, is discussed with reference to the recently proposed “coupled model”. The latter assumes a wide extent of the Variscan Orogen, reaching as far as the marginal Radom-Kraśnik Fold-and-Thrust Belt linked with the Bohemian Massif through a major basal detachment. It is concluded that the “decoupled model” is more consistent with the documented seismic and structural evidence as well as with the present knowledge of the heterogeneous pre-Devonian basement in southern Poland.