High-pressure/low-temperature metamorphism of the Ko-hegy gneiss, Sopron (W-Hungary); phengite barometry and fluid inclusions

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Abstract

A first record of Alpine high-pressure/low-temperature, blueschist-facies metamorphism is reported from a garnet-beating 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 association with biotite, K-feldspar, quartz and grossular-rich garnet. Peak metamorphic pressure conditions were about 1.2 GPa at 450-500°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 salinity (10.9-12.4 NaCl eq. wt%) NaCl-H20 inclusions in albite with Th = 178-217°C. This type may be the high-pressure fluid, reequilibrated at lower pressures. 2. Secondary, intermediate salinity (7.1-12.4 NaCl eq. wt%) NaCl-H20 inclusions in quartz veins, cross-cutting the S2 schistosity. Homogenisation temperatures range from 85 to 176°C. 3. Secondary, high salinity CaCl2-H2O ± NaCl inclusions (24 and 28.4 CaCl2 eq. wt%) in quartz veins, cross-cutting the S2 schistosity. Homogenisation temperatures range between 61 and 171°C. The type 2 and 3 fluids are connected with retrograde metamorphism. 4. Secondary, high salinity NaCl-CaCl2-H2O inclusions with salinity of about 20.4 and 22.2 NaCl eq. wt% and homogenisation temperature between 64°C and 99°C.

Original languageEnglish
Pages (from-to)917-925
Number of pages9
JournalEuropean Journal of Mineralogy
Volume8
Issue number5
Publication statusPublished - Sep 1 1996

Keywords

  • Blueschist facies
  • Eastern Alps
  • Fluid inclusions
  • Phengite
  • Sopron

ASJC Scopus subject areas

  • Geochemistry and Petrology

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