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Primary carbonate/CO 2 inclusions in sapphirine‐bearing granulites from central Sri Lanka
Author(s) -
Bolder-Schrijver,
Leo M. Kriegsman,
Touret
Publication year - 2000
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1046/j.1525-1314.2000.00254.x
Subject(s) - granulite , magnesite , geology , metamorphic rock , fluid inclusions , geochemistry , mineralogy , carbonate , cordierite , inclusion (mineral) , hydrothermal circulation , facies , chemistry , magnesium , geomorphology , biochemistry , organic chemistry , structural basin , seismology , catalysis
High‐density CO 2 ‐rich fluid inclusions from a sapphirine‐bearing granulite (Hakurutale, Sri Lanka) have been studied by microthermometry, Raman spectrometry and SEM analysis. Based on textural evidence, two groups of inclusions can be identified: primary, negative crystal shaped inclusions (group I) and pseudo‐secondary inclusions, which experienced a local, limited post‐trapping modification (group II). Both groups contain magnesite as a daughter mineral, occurring in a relatively constant fluid/solid inclusion volume ratio (vol solid =0.15 total volume). CO 2 densities for group I and II differ only slightly. Both groups contain a fluid, which was initially trapped at peak metamorphic conditions as a homogeneous (CO 2 +MgCO 3 ) mixture. Thermodynamic calculations suggest that such a fluid (CO 2 +15 vol% MgCO 3 ) is stable under granulite facies conditions. After trapping, magnesite separated upon cooling, while the remaining CO 2 density suffered minor re‐adjustments. A model isochore based on the integration of the magnesite molar volume in the CO 2 fluid passes about 1.5–2 kbar below peak metamorphic conditions. This remaining discrepancy can be explained by the possible role of a small quantity of additional water.