Evolution of the Penninic Basement of the Eastern Alps

Abstract

Penninic basement is exposed in the Venediger nappe system of the Tauern window. Three lithostratigraphic units are distinguished: (1) the ophiolitic Stubach group which consists of splinters derived from back-arc oceanic crust, (2) the Habach-Storz group which is dominated by volcanic protoliths and represents remnants of an island arc probably formed on top of the back-arc oceanic crust, and (3) the Zentralgneis group which is composed of large volumes of Variscan granitoids. The island arc experienced maturation during its evolution in the Late Proterozoic and Early Palaeozoic. Carboniferous high-grade metamorphism and granitoid formation reflect a collisional event and collision- and subduction-related magma generation. S-type, originally cordieritebearing, high-K granitoids, I-type high-K granitoids, and I-type medium-K granitoids form a sequence of decreasing age. Permian magmatism with a tendency to the A-type indicates an intraplate setting and signalizes the end of the Variscan orogenic cycle. The evolution of the basement in the Tauern window shows the progressive buildup of continental crust by long-lived subduction activity, starting in an intra-oceanic environment. The overall picture is reminiscent of granite-greenstone belts.