P-T gradient of Eo-Alpine metamorphism within the Austroalpine basement units east of the Tauern Window (Austria)

A petrological study has been undertaken in the Austroalpine basement units, along a SSE-NNW profile across the northern parts of the Saualpe Complex in the Seetal Alps, the Micaschist-Marble Complex (Rappold and Wolz Units) in the Wolz Tauern and the Speik Complex with Permian cover sequences at Hochgrossen Massif in the Rottenmann Tauern. With exception of the Permian cover rocks all units experienced Pre-Alpine as well as Eo-Alpine metamorphism. Relicts of early Variscan eclogite facies metamorphism (397 Ma) are preserved in the Speik Complex in the Hochgrossen Massif. Different compositional zoning and inclusion patterns in garnet porphyroblasts from the Rappold and Wolz Units allow to distinguish two Pre-Alpine metamorphic events: a Permian (similar to 250 Ma) low-P/high-T and an Upper Carboniferous (330 Ma?) medium-pressure metamorphism of amphibolite facies conditions. Eo-Alpine metamorphism (similar to 100 Ma) is characterized by a southward grading from upper greenschist facies (510 +/- 10degreesC and 0.8 GPa) in the Permian cover sequences in the north, through amphibolite facies (600-650degreesC and 1.0-1.1 GPa) in the Wolz and Rappold Units to eclogite facies (690 +/- 20degreesC and 1.8 +/- 0.1 GPa) in the Saualpe Complex in the south. The P-T conditions of Eo-Alpine metamorphism estimated for the different Austroalpine units indicate a subduction type geothermal gradient of 10-16degreesC/km. The rocks that formed at different P-T conditions are now exposed within south dipping thrust units in the Eastern Alps.