Cenozoic Evolution of the Koralm Complex

The evolution of the Koralm Complex during the Cretaceous (Eo-Alpine evolution) is very well constrained by petrological studies and data. This, together with geochronological work, facilitated a detailed reconstruction of the pressure-temperature-time evolution, in particular from the Permian to the Late Cretaceous. During the last few years detailed structural studies gave access to the reconstruction of the tectonic evolution during the Late Creatceous. In these studies it was shown, that the exhumation of high-pressure rocks was related to an extensional shear zone (“Plattengneis shear zone”), which was activated at high-pressure conditions. At shallow crustal levels, the exhumation of the Koralm Complex was accommodated by low-angle normal faults along its southern and northern margins. Deformation along these normal faults occurred under greenschist facies metamorphic conditions. Along its southern margins, a low-angle normal fault forms the contact between the Koralm Complex below, and the Plankogel Complex above; in the north/northeast, a low-angle normal fault forms the contact between the Koralm Complex and the Paleozoic of Graz. Extension accommodated by these normal faults triggered the formation of the Gosau sedimentary basins during the Late Cretaceous as well. Thus, there is a direct relationship between the exhumation of the Koralm eclogites, the structural evolution of the Plattengneis shear zone, and the formation of the Gosau sedimentary basins in the cent