Evolution of H2O content in a polymetamorphic terrane: The Plattengneiss Shear Zone (Koralpe, Austria)

Abstract

The Koralpe of the Eastern European Alps experienced high-temperature/ low-pressure metamorphism (∼650 °C and 6.5 kbar) during the Permian and eclogite facies metamorphism (∼700 °C and 14 kbar) during the Eo-Alpine (Cretaceous) metamorphic event. In the metapelitic Plattengneiss shear zone that constitutes much of the Koralpe, the second metamorphism caused only partial re-equilibration of the assemblages formed during the first metamorphism. It is shown here that the Eo-Alpine mineral assemblage, garnet + biotite + muscovite + plagioclase + quartz (with or without yanite), formed under low water activity conditions that are consistent with the level of dehydration that occurred during the P..