KINEMATIC DATA ON MAJOR VARISCAN STRIKE-SLIP FAULTS AND SHEAR ZONES IN THE POLISH SUDETES, NORTHEAST BOHEMIAN MASSIF

The still highly disputable terrane boundaries in the Sudetic segment of the Variscan belt mostly seem to follow major strike-slip faults an d shear zones. Their kinematics, expected to place important constrain ts on the regional structural models, is discussed in some detail. The most conspicuous is the WNW-ESE Intra-Sudetic Fault Zone, separating several different structural units of the West Sudetes. It showed duct ile dextral activity and, probably, displacement magnitude of the orde r of tens to hundreds kilometres, during late Devonian(?) to early Car boniferous times. In the late Carboniferous (to early Permian?), the s ense of motion on the Intra-Sudetic Fault was reversed in a semi-britt le to brittle regime, with the left-lateral offset on the fault amount ing to single kilometres. The north-south trending Niemcza and northea st-southwest Skrzynka shear zones are left-lateral, ductile features i n the eastern part of the West Sudetes. Similarly oriented (northeast- southwest to NNE-SSW) regional size shear zones of as yet undetermined kinematics were discovered in boreholes under Cenozoic cover in the e astern part of the Sudetic foreland (the Niedzwiedz and Nysa-Brzeg she ar zones). One of these is expected to represent the northern continua tion of the major Stare Mesto Shear Zone in the Czech Republic, separa ting the geologically different units of the West and East Sudetes. Th e Rudawy Janowickie Metamorphic Unit, assumed in some reconstructions to comprise a mostly strike-slip terrane boundary, is characterized by ductile fabric developed in a thrusting regime, modified by a superim posed normal-slip extensional deformation. Thrusting-related deformati onal fabric was locally reoriented prior to the extensional event and shows present-day strike-slip kinematics in one of the sub-units. The Sudetic Boundary Fault, although prominent in the recent structure and topography of the region, was not active as a Variscan strike-slip fa ult zone. The reported data emphasize the importance of syn-orogenic s trike-slip tectonics in the Sudetes. The recognized shear sense is com patible with a strike-slip model of the northeast margin of the Bohemi an Massif, in which the Kaczawa and Gory Sowie Units underwent late De vonian-early Carboniferous southeastward long-distance displacement al ong the Intra-Sudetic Fault Zone from their hypothetical original posi tion within the Northern Phyllite Zone and the Mid-German Crystalline High of the German Variscides, respectively, and were juxtaposed with units of different provenance southwest of the fault. The Intra-Sudeti c Fault Zone, together with the Elbe Fault Zone further south, were su bsequently cut in the east and their eastern segments were displaced a nd removed by the younger, early to late Carboniferous, NNE-SSW trendi ng, transpressional Moldanubian-Stare Mesto Shear Zone.