Transpresja i ekstensja w Rudawach Janowickich (Sudety Zachodnie)

Zbigniew Cymerman



This paper presents the complex structural and kinematic history of metamorphic rocks from the Rudawy Janowickie metamorphic complex (RJMC), the eastern part of the Izera-Karkonosze core complex (Western Sudetes). The metamorphic rocks of the RJMC are divided into three lithotectonic units: (1) the Kowary unit; (2) the Niedamirów unit; and (3) the Leszczyniec unit. The RJMC is characterized by two tectonic stages: D1 transpressional event and D2 extensional one. The older transpressional (D1) deformation occurred during HP-MT metamorphic conditions (M1). Regional, in general subhorizontal NNE-SSW stretching lineation (L1) on steeply deeping foliation (S1) and shear criteria (S-C structures, C' shear bands) observed in the Leszczyniec and Niedamirów units indicate a southward displacement of the hanging-wails during D1 deformation. However, some domains in the Leszczyniec unit show a more complicated kinematics probably related to a strain partitioning during dextral transpression. An important regional extensional ductile deformation (D2) is best described from the Kowary orthogneisses. The well developed S2 mylonitic foliation strikes NNE-SSW and dips moderately to the east. Ductile and brittle structures indicate that deformation (D2) within the RJMC was due to noncoaxial deformation. Extensional deformation occurred under conditions of retrograde metamorphism from amphibolite-facies conditions to greenschist facies. Regional ca. W-E stretching Iineations and shear criteria indicate an eastward ductile displacement of the hanging wall during the Visean D2 extension. At least some movement on the shear zones occurred at depths of ca. 25 km during late-Variscan amphibolite facies metamorphism, but shear zone fabric may be found in some parts of the Karkonosze granites. The shearing events may thus have been active over a period of as much as 20 Ma. The main D2 extensional deformation probably was contemporaneous with, or slightly preceded the extensional collapse of the crust directed to the east, which initiated formation of the Intra-Sudetic basin. This basin formed along the hanging wall of the normal shear zone and were tilted moderately towards the east during the Sudetic phase. The RJMC is a major detachment belt that played an important role in the Carboniferous extension of the Sudetes.

Pełny tekst: