LARGE-SCALE THIN-SKINNED TECTONICS IN THE EASTERN BOUNDARY OF THE BOHEMIAN MASSIF

Two new seismic reflection profiles and a deep borehole reveal thin-skinned thrusting on the easternmost part of the Rheno-Hercynian zone of the Variscan belt of Europe. Above Precambrian Brunnia basement the profiles show three different seismic zones within the compressed Palaeozoic sedimentary section. The borehole data suggest that the lower zone is a deformed "paraautochthonous" Brunnia basement covered by Upper Devonian and Lower Carboniferous shelf carbonates with numerous local overthrusts. This zone is overthrust by the uppermost seismic zone of Lower Carboniferous Culm flysch wedge and in the west by the eastward dipping zone. This intervening seismic zone on the east end of the profiles is a foreland dipping thrust sheet of another Culm flysch complex (mainly Horni Benesov Formation), or seismic crocodiles in the sense of Meissner (1989). Inverted metamorphism between the Culm flysch and the Brunnia shelf sequences encountered in the well Potstat-1, and strong slaty cleavage in the intervening zone, suggests that the upper zone is allochthonous, heaving been thrust from deeper levels tens of kilometres eastward over carbonates. Imbrication of the carbonates as part of the footwall suggest relatively strong coupling between the Palaeozoic sediments and underlying basement at the time of thrusting.