Alpine P-T path of micaschists and related orthogneiss veins near Obrennberg (W-Hungary, Eastern Alps)

Abstract

High-pressure metapelites with the assemblage kyanite-staurolite-garnet ′ chloritoid-biotite-muscovite-plagioclase-quartz and crosscutting gneiss veins were studied in the Sopron Mountains near Obrennberg (Hungary, Eastern Alps). Different garnet generations were investigated by textural analysis and study of garnet zoning from different textural domains from both the micaschist and the gneiss veins. Thermobarometry of subsequent garnet generations and the surrounding mineral assemblage was used to reconstruct the Alpine P-T path of the metamorphic rocks during the Alpine orogenesis. Peak pressure conditions (1390-1470 MPa) are recorded by high-Si phengites (Si = 7.03 a.p.f.u.) and temperatures by white mica-garnet-albite-quartz assemblage at about 550-600 °C. This is in good agreement with the peak pressures obtained from the massive orthogneisses of the area. Gneiss veins crosscutting the micaschist show slightly lower peak pressures between 1230 and 1280 MPa at similar temperatures (575-590 °C). Subsequent garnet generations and associated mineral assemblages show decreasing pressure with slightly decreasing temperature. Textural observations, white mica chemistry and comparison of garnet zoning trends provided additional evidence on the formation of leucophyllites during retrograde metamorphism.