LATE CRETACEOUS, SYNOROGENIC, LOW-ANGLE NORMAL FAULTING ALONG THE SCHLINIG FAULT (SWITZERLAND, ITALY, AUSTRIA) AND ITS SIGNIFICANCE FOR THETECTONICS OF THE EASTERN ALPS

The Schlinig fault at the western border of the Otztal nappe (Eastern Alps), previously interpreted as a west-directed thrust, actually repr esents a Late Cretaceous, top-SE to -ESE normal fault, as indicated by sense-of-shear criteria found within cataclasites and greenschist-fac ies mylonites. Normal faulting postdated and offset an earlier, Cretac eous-age, west-directed thrust at the base of the Otztal nappe. Shape fabric and crystallographic preferred orientation in completely recrys tallized quartz layers in a mylonite from the Schlinig fault record a combination of (1) top-east-southeast simple shear during Late Cretace ous normal faulting, and (2) later north-northeast-directed shortening during the Early Tertiary, also recorded by open folds on the outcrop and map scale. Offset of the basal thrust of the Otztal nappe across the Schlinig fault indicates a normal displacement of 17 km. The fault was initiated with a dip angle of 10 degrees to 15 degrees (low-angle normal fault). Domino-style extension of the competent Late Triassic Hauptdolomit in the footwall was kinematically linked to normal faulti ng. The Schlinig fault belongs to a system of east-to southeast-dippin g normal faults which accommodated severe stretching of the Alpine oro gen during the Late Cretaceous. The slip direction of extensional faul ts often parallels the direction of earlier thrusting (top-W to top-NW ), only the slip sense is reversed and the normal faults are slightly steeper than the thrusts. In the western Austroalpine nappes, extensio n started at about 80 Ma and was coeval with subduction of Piemont-Lig urian oceanic lithosphere and continental fragments farther west. The extensional episode led to the formation of Austroalpine Gosau basins with fluviatile to deep-marine sediments. West-directed rollback of an east-dipping Piemont-Ligurian subduction zone is proposed to have cau sed this stretching in the upper plate.