Nahcolite in fluid inclusions from the Ryoke metamorphic rocks and its implication for fluid genesis
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- HOSHINO Kenichi
- Department of Earth and Planetary Systems Science, Hiroshima University
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- NAGATOMI Ai
- Masutomi Geology Museum
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- WATANABE Makoto
- Department of Earth and Planetary Systems Science, Hiroshima University
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- OKUDAIRA Takamoto
- Department of Geosciences, Osaka City University
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- BEPPU Yuki
- Department of Geosciences, Osaka City University
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Abstract
Nahcolite (NaHCO3) has been found in fluid inclusions in quartz veins hosted by the Ryoke metamorphic rocks in Kasado-Jima (Island), Yamaguchi Prefecture, Japan. The inclusions are classified into three types: type 1 containing vapor +/− liquid of the H2O-NaCl-CO2-CH4 system, type 2 of H2O-NaCl fluids and type 3 with nahcolite solid. Salinities of the nahcolite-bearing fluids are lower than 4 wt% NaCl eq. Extremely large volume fractions of nahcolite solids, occupying more than 50% of total inclusion volume, and various fluid compositions are indicative of their origin as accidentally trapped ones while the fluids were immiscible below the nahcolite melting temperature (270 °C). A thermodynamic calculation of the nahcolite stability and a phase analysis of the fluids show logaNa+ = 7.4 − pH as the minimum activity at P = 100 MPa and T = 270 °C where the neutral pH = 5.6. Hence, it can be concluded that the original (prior to immiscible state) liquids might have contained high Na+ and low Cl− yielded by an interaction of a low-salinity fluid and Na-bearing minerals such as plagioclase in the host metamorphic rocks below the fractures now occupied by quartz if nahcolite precipitated from boiling fluids.
Journal
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- Journal of Mineralogical and Petrological Sciences
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Journal of Mineralogical and Petrological Sciences 101 (5), 254-259, 2006
Japan Association of Mineralogical Sciences
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Details
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- CRID
- 1390001206545532416
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- NII Article ID
- 10018106117
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- NII Book ID
- AA11460926
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- COI
- 1:CAS:528:DC%2BD2sXhtVGnug%3D%3D
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- ISSN
- 13493825
- 13456296
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- Text Lang
- en
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- Data Source
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- JaLC
- Crossref
- CiNii Articles
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- Abstract License Flag
- Disallowed