Fold-thrust-belt geometry and detailed structural evolution of the Silesian nappe – eastern part of the Polish Outer Carpathians (Bieszczady Mts.)

Abstract

On the basis of field studies of mesoscopic structures, and analysis of radar and aerial photos together with seismic data, the structure and structural evolution of a part of the Silesian nappe was established. In the study area the Silesian nappe comprises two tectonic units: the Central Carpathian Depression and the Fore-Dukla thrust sheet, separated by a fault. The Central Carpathian Depression is built of several mapscale slices. The slices comprise map-scale NE-verging anticlines, with additional synclines to the south-east. The slices are separated by steeply dipping forelimb-thrusts, which connect together at a depth of ca. 6-7 km into a single sole thrust and form a leading imbricate fan. To the west of the Rabe-Baligrod fault zone the fault between the Central Carpathian Depression and the Fore-Dukla thrust sheet is a typical thrust. Eastwards from this fault zone it becomes a steeply NE-dipping normal fault. The Silesian nappe is cut by map-scale oblique and transverse, mainly strike-slip faults – some of them are tear faults. Longitudinal strike-slip faults indicate dextral movement along the pre-existing thrusts. The structural evolution of the Silesian nappe comprises here eight pre-, syn- and post-orogenic stages beginning with the formation of clastic veins, followed by folding, thrusting, strike-slip faulting and terminating with normal faulting.