CONTRASTING CHEMISTRY AND HOC-ISOTOPE COMPOSITION OF GREENSCHIST-FACIES, HERCYNIAN AND ALPINE METAMORPHIC FLUIDS (WESTERN CARPATHIANS)

Microthermometry and stable isotope data enable us to distinguish betw een two contrasting sets of fluids involved in the Hercynian and Alpin e metamorphic events in the Western Carpathians. High-temperature smok y quartz (450-500 degrees C) was probably formed during the syn-kinema tic phase of the Hercynian metamorphism, when chemical and isotopic eq uilibrium had been established between aqueous solutions and the surro unding rocks. This is indicated by fixed Na/Ca ratios and narrow range s of delta D and delta(18)O values in the inclusion fluids (-59 +/- 5 parts per thousand and +7 to +7.5 parts per thousand SMOW, respectivel y), In contrast, Alpine quartz precipitating at temperatures between 3 00 degrees and 400 degrees C in extension-related structures displayed a non-equilibrium signature characterized by a much larger compositio nal and isotopic variability. Presence of CO2 in quartz from granitoid -hosted shear zones indicates externally derived fluids with delta(13) C values between -11.9 to - 7.7 parts per thousand PDB. These values c an be interpreted to reflect an admixture of a lighter CO2 generated b y decomposition of organic matter in underlying low- to medium-grade s ediments, The essentially identical isotopic composition of the inclus ion CO2 from the presumably Hercynian as well as Alpine metamorphic qu artzes supports the concept of Hercynian overthrusting nf granitoids o nto metamorphites in the crystalline basement of the Western Carpathia ns.