At the border of peri-Gondwana and Baltica: the structure of the eastern termination of the Variscan belt

The termination of the eastern Variscan belt has long been a matter of debate because it is deeply concealed beneath younger sediments. Its geometry has been addressed by the two competing hypotheses of the Variscan orocline and right-lateral strike-slip tectonics. We compiled a set of new gravity and magnetic maps for the Czech Republic, Poland and eastern Germany to track Variscan structures in the subsurface. These maps clearly show that the Rheno-Hercynian Suture turns by almost 90° east of the Harz Mountains in Germany and continues into Poland towards the ESE. Our results therefore favour the concept of a semi-orocline that terminates in the east against the Brunovistulian Block. The pattern of magnetic and gravity anomalies, combined with geological evidence, indicates two superimposed stages of accretion in the eastern Variscan belt. The initial west–east convergence led to the formation of the NNE–SSW-trending structures that dominate the southern Bohemian Massif. These structures were overprinted by an important north–south-shortening event that shaped the WNW–ESE-oriented features. The latter run parallel to the Baltica margin and dominate the area NE of the Elbe Fault. This is consistent with seismic data showing large-scale underthrusting of the Baltica crust beneath the Variscan belt over a distance of at least 100 km.