The Middle Austro-Alpine Sieggraben structural complex – new data on geothermobarometry

The Sieggraben structural complex is located in the Eastern Alps and went through complicated tectonothermal evolution. Lithotypes are represented by metabasic rocks, metacarbonates, metapelites, and serpentinites. Metabasites consist of amphiboles and eclogites. The whole unit underwent two MP/HP metamorphic stages – a D1 prograde burial stage and a D2 exhumation stage. The D1 prograde burial stage resulted in the forming of Omp with over 30 % of Jd component, Am1, Pl1. P-T conditions of the D1 stage were calculated at 610–650 °C (Grt-Cpx geothermometer) and 16–17 kbar (Grt-Cpx-Pl-Qtz geobarometer). The D2 exhumation stage resulted in the forming of Am2, Pl2, and Cpx2 mineral association. P-T conditions of the D2 stage were set to 700 °C at 12 kbar by Grt-Bt geothermometer and Grt-Pl-Ky-Qtz geothermobarometer. Previously published P-T path was recalculated using new geothermobarometry calculations.