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Exhumation related crystallographic preferred orientations in Cretaceous high pressure rocks of the Eastern Alps

The Saualpe-Koralpe high pressure (HP) complex as well as the HP units of the Pohorje mountains formed during the Cretaceous orogenic cycle in the Eastern Alps. Within these units eclogite bodies can be found, which were probably emplaced along the rift zone that led to the opening of the Meliata ocean. After closure of the ocean ongoing convergence led to underplating within the lower plate, which led to the formation of the Austroalpine nappe stack. During subduction, the Saualpe, Koralpe and Pohorje units reached peak pressure conditions of 2.2-2.4 GPa/630-690°C, 1.8-1.9 GPa/670°C and 3.0–3.7 GPa/710–940 °C, respectively. PT-analyses, microstructural investigations and dating predict different contrasting models for the subsequent exhumation of these units.

Here, we investigate the deformational history of these units during their exhumation. We sampled sets of pristine eclogites, retrograde amphibolite facies shear zones as well as neighboring gneisses surrounding the eclogite lenses. The samples were analyzed by electron backscatter diffraction (EBSD) to determine their crystallographic preferred orientation (CPO) and deformation mechanisms. Both omphacite in pristine eclogites and hornblende in the amphibolite facies shear zones show a pronounced CPO. Hornblende yields distinct signs of dynamic recrystallization by subgrain rotation within the shear zones. Quartz CPO was analyzed in both the eclogites and the surrounding gneiss matrix. Results indicate a shear sense reversal during the exhumation of the Pohorje eclogites.

In this study we show CPO data that recorded the deformational path of these rocks from eclogite facies conditions up to the exhumation to crustal levels.


Ruth Keppler1, Niko Froitzheim1
1Universität Bonn, Germany
GeoBerlin 2023