HIGH-PRESSURE LOW-TEMPERATURE METAMORPHISM OF THE KO-HEGY GNEISS, SOPRON (W-HUNGARY) - PHENGITE BAROMETRY AND FLUID INCLUSIONS/

A first record of Alpine high-pressure/flow-temperature, blueschist-fa cies metamorphism is reported from a garnet-bearing orthogneiss in the vicinity of Sopron area, western Hungary, in the Grobgneiss series of the Eastern Alps. The high-pressure conditions are marked by phengite -3T with Si contents up to 3.49 atoms p.f.u., which is in close associ ation with biotite, K-feldspar, quartz and grossular-rich garnet. Peak metamorphic pressure conditions were about 1.2 GPa at 450-500 degrees C. Some of the white micas preserved low-Si (about 3.1 atoms p.f.u.) and high-Ti magmatic cores. Four types of aqueous fluid inclusions can be distinguished in the studied rock: 1. Primary, intermediate salini ty (10.9-12.4 NaCl eq. wt%) NaCl-H2O inclusions in albite with T-h = 1 78-217 degrees C. This type may be the high-pressure fluid, reequilibr ated at lower pressures. 2. Secondary, intermediate salinity (7.1-12.4 NaCl eq. wt%) NaCl-H2O inclusions in quartz veins, cross-cutting the S-2 schistosity. Homogenisation temperatures range from 85 to 176 degr ees C. 3. Secondary, high salinity CaCl2-H2O +/- NaCl inclusions (24 a nd 28.4 CaCl2 eq. wt%) in quartz veins, crosscutting the S-2 schistosi ty. Homogenisation temperatures range between 61 and 171 degrees C. Th e type 2 and 3 fluids are connected with retrograde metamorphism. 4. S econdary, high salinity NaCl-CaCl2-H2O inclusions with salinity of abo ut 20.4 and 22.2 NaCl eq. wt% and homogenisation temperature between 6 4 degrees C and 99 degrees C.