Thermobarometry of metasediments and metabasites from the Eclogite zone of the Hohe Tauern, Eastern Alps, Austria

Metamorphic P–T conditions of calcareous metasediments and metabasites from the eclogite zone of the Hohe Tauern region were evaluated based on the application of various geothermobarometers, e.g. programs PTt PATH, TWEEQU and THERMOCALC. Average P–T values in metasediments are c. 9.0–10.2 kbar, 552–565 °C due to the late tertiary alpine metamorphic event. In one sample, only the inclusion of omphacite in garnet testifies the earlier alpine high P event. In metabasites, however, this event dominates with conditions at c. 19.2–22.4 kbar, 594–627 °C. Retrogression at lower pressure is only rarely documented in the formation of albite. Pseudosections calculated with Thermocalc in the simplified NCFMASH system for various bulk compositions related to sample eclogite 2447 are in approximate accordance with a sequence of mineral assemblages: omphacite+paragonite+zoisite+hornblende (prograde inclusions in garnet)>garnet+omphacite+kyanite (matrix phases at P–T maximum)>paragonite+zoisite+hornblende (secondary phases on retrograde path). Formation of these hydrous phases probably took place during decompression at slightly lower P–T conditions in the presence of restricted amounts of H2O.