Tectonic history of Eoalpine high-pressure rocks – new results and open questions

The Eoalpine high pressure (HP) belt is part of the Austroalpine basement and reached eclogite facies conditions at 100 to 90 Ma during the Cretaceous Alpine orogenic cycle. It extends over 350 km from the Texel Complex in the west over the Saualpe and Koralpe units to the Pohorje Mountains in the east. While HP to ultra HP conditions are well established, there is still debate on the tectonic history of these rocks. Early studies suggest a continuous subduction along the suture of the Meliata ocean. Other studies suggest a younger intra-continental subduction zone, which formed along a pre-existing weakness caused by Permian rifting. Also, the exhumation mechanisms of these rocks remain unclear. Exhumation through an extrusion wedge has been suggested for the rocks of the Saualpe. The contact toward the hanging wall is interpreted as a low-angle normal fault active during extrusion of the HP rocks. Based on crystallographic preferred orientation (CPO) data, exhumation in an extensional regime along a low angle detachment fault was proposed for the Koraple. Slab extraction has been proposed for both the Koralpe and the Pohorje units, based on pseudosection modeling, which suggests a common exhumation path for the HP units with their hanging wall starting at 1.0 GPa. We will present new CPO data of both metabasalts and the surrounding gneiss matrix from the Koralpe as well as the Pohorje mountains, which will shed some light on the deformation mechanisms active during exhumation and on the overall tectonic history of these rocks.