Structural evolution of an antiformal window: the Scheiblingkirchen Window (Eastern Alps, Austria)

The Scheiblingkirchen window, a Lower Austroalpine tectonic window at the eastern margin of the Eastern Alps (Austria) was formed during Late Cretaceous continent–continent collision. Structural investigations including structural mapping, microstructural studies and texture analysis revealed a decompression-related three-stage tectonic history of Lower Austroalpine units during the formation of the Scheiblingkirchen window. tra-Lower Austroalpine nappe stacking was by top-to-the-N out-of-sequence thrusting of the Kirchberg fold nappe over the Wechsel nappe under lower greenschist facies metamorphic conditions. The structural expression of the stacking event (D1) comprises a penetrative foliation containing a N–S trending stretching lineation, isoclinal recumbent folds trending subparallel to the stretching lineation and ultramylonites. Quartz and calcite microstructures indicate that dynamic recrystallization processes accompanied deformation. Their commonly moderately developed lattice preferred orientation record dominant slip on the prism and rhomb planes parallel to 〈a〉. bsequent exhumation of previously stacked rocks is related to the formation of foliation-parallel mylonitic shear zones within an E–W extensional regime (D2). Microstructures and textures suggest similar deformation temperatures during thrusting and extension. superimposed phase of NW–SE oriented horizontal shortening (D3) was accommodated by large- and small-scale upright folding of the area around NE–SW trending axes and by backthrusting leading to the antiformal doming of the Scheiblingkirchen Window. Subsequent subvertical flattening resulting from the shortening phase led to the formation of NE–SW trending, outcrop-scale open recumbent folds. Low temperature deformation conditions as inferred from the low degree of recrystallization of quartz and calcite aggregates and the dominance of glide on the basal planes point to a cooling-related deformation event.