Kinematic data on major Variscan strike-slip faults and shear zones in the Polish Sudetes, northeast Bohemian Massif

Abstract

The still highly disputable terrane boundaries in the Sudetic segment of the Variscan belt mostly seem to follow major strike-slip faults and shear zones. Their kinematics, expected to place important constraints 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 ductile dextral activity and, probably, displacement magnitude of the order of tens to hundreds kilometres, during late Devonian(?) to early Carboniferous times. In the late Carboniferous (to early Permian?), the sense of motion on the Intra-Sudetic Fault was reversed in a semi-brittle to brittle regime, with the left-lateral offset on the fault amounting to single kilometres. The north–south trending Niemcza and north-east–southwest Skrzynka shear zones are left-lateral, ductile features in 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 eastern part of the Sudetic foreland (the Niedźwiedź and Nysa-Brzeg shear zones). One of these is expected to represent the northern continuation of the major Stare Mesto Shear Zone in the Czech Republic, separating the geologically different units of the West and East Sudetes. The 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 superimposed normal-slip extensional deformation. Thrusting-related deformational 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 fault zone. The reported data emphasize the importance of syn-orogenic strike-slip tectonics in the Sudetes. The recognized shear sense is compatible with a strike-slip model of the northeast margin of the Bohemian Massif, in which the Kaczawa and Góry Sowie Units underwent late Devonian–early Carboniferous southeastward long-distance displacement along the Intra-Sudetic Fault Zone from their hypothetical original position 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-Sudetic Fault Zone, together with the Elbe Fault Zone further south, were subsequently cut in the east and their eastern segments were displaced and removed by the younger, early to late Carboniferous, NNE–SSW trending, transpressional Moldanubian–Stare Mesto Shear Zone.

The origin of the Popiel peridotite (Western Sudetes, SW Poland): Metamorphism of the island arc tholeiitic cumulate

“…It is lo cated north-east of the vil lage of Janowice Wielkie (Fig. 1), im me di ately south of the Intra-Sudetic Fault, one of the ma jor Variscan geolog i cal bor ders in the north-east part of the Bo he mian Mas sif, in Cen tral Eu rope (Aleksandrowski et al, 1997).…”

“…The peridotite is sur rounded by low-grade metabasic rocks ("striped metabasites"), be long ing to the Kowary Unit of the Rudawy Janowickie Com plex (Aleksandrowski et al, 1997), sur round ing the Variscan Karkonosze gran ite to the east and north-east. Popiel Hill is sit u ated within ca.…”

Palaeodrainage systems at the basal unconformity of the Bohemian Cretaceous Basin: roles of inherited fault systems and basement lithology during the onset of basin filling

“…The onset of activity of the WNW to NW-striking dextral ductile shear zones in the Variscides is dated as Late Devonian-Viséan (e.g., Aleksandrowski et al 1997, Matte et al 1986, i.e., before the formation of the Late Carboniferous extensional basins. Later activity occurred at < 295 Ma, in late Stephanian to early Permian, with dextral motions interpreted by Pitra et al (1999), and putative sinistral kinematics suggested by Mattern (2001).…”

Lithospheric mantle beneath NE part of Bohemian Massif and its relation to overlying crust: new insights from Pilchowice xenolith suite, Sudetes, SW Poland

“…We discuss the details of mantle evolution recorded in the xenoliths and comment on its significance to the overall characteristics of the Lower Silesian mantle domain of the European Variscan orogen. U p p e r E l b e F a u l t Z o n e O d r a F a u l t Z o n e I n t r a -S u d e t i c F a u l t Z o n e The Pilchowice basanite is located directly on the IntraSudetic Fault (ISF)-a major Variscan NW-SE trending, long-living (Devonian-Carboniferous, Don 1984 or Devonian-Permian; Aleksandrowski et al 1997) dislocation transecting whole the Sudetes. In the vicinity of Pilchowice the ISF separates Karkonosze-Izera Block (represented by gneisses) from the mica schists of Kaczawa Complex (Fig.…”