LATE CRETACEOUS EXHUMATION OF THE METAMORPHIC GLEINALM DOME, EASTERN ALPS - KINEMATICS, COOLING HISTORY AND SEDIMENTARY RESPONSE IN A SINISTRAL WRENCH CORRIDOR

The metamorphic Gleinalm dome, Eastern Alps, was uplifted and exhumed within a releasing structure in a sinistral wrench corridor during the Late Cretaceous. The dome is confined by a system of ductile shear zones including low-angle normal faults and steep sinistral tear faults which define a large releasing structure with the metamorphic dome in its center. The fabrics developed within all ductile shear zones record processes which were operating during decreasing temperatures from initial epidote-amphibolite/upper greenschist facies conditions (with crystal plastic fabrics in quartz) to temperatures below ca. 300 degrees C (with predominantly cataclastic fabrics). A cooling path based on 40Ar/39Ar amphibole (95.4 +/- 1.2 Ma) and muscovite ages (87.6 +/- 0.6; 84.3 +/- 0.7 Ma) together with sphene, zircon and apatite fission track data indicate cooling through ca. 500 degrees C at ca. 94 Ma to below ca. 250-200 degrees C at 65 Ma. Subsidence of the adjacent Late Cretaceous Kainach Gosau basin occurred synchronously with cooling and uplift of the Gleinalm dome. Internal depositional patterns record rapid subsidence at the time of cooling with internal synsedimentary block rotation above an intra-crustal ductile normal fault. The sinistral wrench corridor of the Eastern Alps developed by sinistral displacement of the Austroalpine units against a relatively stable Europe during the Late Cretaceous.