The DAV and Periadriatic fault systems in the Eastern Alps south of the Tauern window

Alpine deformation of Austroalpine units south of the Tauern window is domi nated by two kinematic regimes. Prior to intrusion of the main Periadriatic plutons at similar to 30 Ma, the shear sense was sinistral in the current orientation, with a minor northside-up component. Sinistral shearing locall y overprints contact metamorphic porphyroblasts and early Periadriatic dyke s. Direct Rb-Sr dating of microsampled synkinematic muscovite gave ages in the range 33-30 Ma, whereas pseudotachylyte locally crosscutting the myloni tic foliation gave an interpreted Ar-40-Ar-39 age of similar to 46 Ma. The transition from sinistral to dextral (transpressive) kinematics related to the Periadriatic fault occurred rapidly, between solidification of the earl ier dykes and of the main plutons. Subsequent brittle-ductile to brittle fa ults are compatible with N-S to NNW-SSE shortening and orogen-parallel exte nsion. Antithetic Riedel shears are distinguished from the previous sinistr al fabric by their fine-grained quartz microstructures, with local pseudota chylyte formation. One such pseudotachylyte from Speikboden gave a Ar-40-Ar -39 age of 20 Ma, consistent with pseudotachylyte ages related to the Peria driatic fault. The magnitude of dextral offset on the Periadriatic fault ca nnot be directly estimated. However, the jump in zircon and apatite fission -track ages establishes that the relative vertical displacement was similar to4-5 km since 24 Ma, and that movement continued until at least 13 Ma.