"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism
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Accession number;04A0874346
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| Title;"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism |
| Author;
SANTOSH M
(Kochi Univ., Kochi, Jpn)
TSUNOGAE T
(Univ. Tsukuba, Ibraki, Jpn)
YOSHIKURA S
(Kochi Univ., Kochi, Jpn)
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Journal Title;J Mineral Petrol Sci
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Journal Code:G0150B
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ISSN:1345-6296
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VOL.99;NO.4;PAGE.164-179(2004)
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| Figure&Table&Reference;FIG.9, TBL.1, REF.38 |
| Pub. Country;Japan |
| Language;English |
| Abstract;Ultrahigh temperature (UHT) granulites in Tonagh Island, Napier Complex, East Antarctica record peak metamorphic pressure-temperature (P-T) conditions of up to 9kbar and 1100.DEG.C.. Sapphirine, garnet, orthopyroxene and quartz in these rocks contain very high density fluid inclusions with melting temperatures close to that of pure CO2 (-56.6.DEG.C.) and homogenization temperatures down to -34.9.DEG.C. translating into high CO2 densities (up to 1.07g/cm3). The UHT granulites of Vizianagram in Eastern Ghats Belt, India which were subjected to extreme crustal metamorphism at >1000.DEG.C. and 8-9kbar also carry very high density (up to 1.15g/cm3) pure CO2 inclusions in quartz adjacent to spinel rimmed by various coronas of sillimanite, orthopyroxene and garnet. Garnets in a granulite facies rock from Salem in southern India that equilibrated at peak P-T conditions of 740-800.DEG.C. and 9-11kbar carry the highest density (1.17g/cm3) pure CO2 yet reported from continental crust. This rock also contains very high density CO2 inclusions in plagioclase and quartz. High density (0.998g/cm3) pure CO2-rich fluid inclusions also occur abundantly within garnets from a mafic granulite in Ampitiya, central Highland Complex, Sri Lanka. The peak P-T conditions of metamorphism of the mafic granulite are around 10.6kbar and 985.DEG.C. with subsequent rapid isothermal decompression along a clock-wise path down to 5.5kbar. In most of the cases above, the representative isochores for the CO2 inclusions either penetrate through or pass very close to the P-T windows defined from mineral phase equilibria indicating that the fluid inclusions were trapped at the time of peak or near post-peak metamorphism. We thus recognize a group of "ultrahigh density" (UHD) CO2-rich fluids that characterize UHT rocks and other granulites formed under extreme crustal metamorphism.... (author abst.) |
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