"Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism
スポンサーリンク
概要
- 論文の詳細を見る
Ultrahigh temperature (UHT) granulites in Tonagh Island, Napier Complex, East Antarctica record peak metamorphic pressure-temperature (P-T) conditions of up to 9 kbar and 1100°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°C) and homogenization temperatures down to −34.9°C translating into high CO2 densities (up to 1.07 g/cm3). The UHT granulites of Vizianagram in Eastern Ghats Belt, India which were subjected to extreme crustal metamorphism at >1000°C and 8-9 kbar also carry very high density (up to 1.15 g/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°C and 9-11 kbar carry the highest density (1.17 g/cm3) pure CO2 yet reported from continental crust. This rock also contains very high density CO2 inclusions in plagioclase and quartz. High density (0.998 g/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 10.6 kbar and 985°C with subsequent rapid isothermal decompression along a clock-wise path down to 5.5 kbar. 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. These fluids contrast sharply with the lower density (generally <1.0 g/cm3) CO2 inclusions commonly reported from normal granulite facies rocks in various terrains. The presence of “synmetamorphic” UHD CO2 within various minerals is consistent with the low water activities predicted by the mineral assemblages in these rocks. Although the source of the CO2 is equivocal, mantle derived mafic magmas could have provided the heat and volatiles required for crustal metamorphism at extreme conditions displayed by these rocks.
- 日本鉱物科学会の論文
- 2004-08-01
著者
-
Santosh M.
Faculty Of Science Kochi University
-
Tsunogae Toshiaki
Institute Of Geoscience The University Of Tsukuba
-
Yoshikura Shin-ichi
Faculty Of Science Kochi University
関連論文
- The birth of Gondwana : Timing and thermal spikes constrained from chemical dating of monazites(Proceedings of the 19^ Symposium on Chronological Studies at the Nagoya University Center for Chronological Research in 2006,Part1)
- Decompression process of mafic granulite from eclogite to granulite facies under ultrahigh-temperature condition in the Kontum massif, central Vietnam
- Ultrahigh temperature sapphirine-osumilite and sapphirine-quartz granulites from Bunt Island in the Napier Complex, East Antarctica -Reconnaissance estimation of P-T evolution -
- Melange fabric of the Chrystalls Beach Complex, southeast Otago, New Zealand
- Sm-Nd garnet ages of retrograde garnet bearing granulites from Tonagh Island in the Napier Complex, East Antarctica: A preliminary study
- Multistage orthopyroxene formation in ultrahigh-temperature granulites of Ganguvarpatti, southern India : implications for complex metamorphic evolution during Gondwana assembly
- Spinel + Quartz association from the Kerala khondalites, southern India : evidence for ultrahigh-temperature metamorphism
- Ultrahigh temperature metamorphism and deep crustal processes : Introduction
- Carbonic fluid inclusions in ultrahigh-temperature metamorphic rocks from Tonagh Island in the Archean Napier Complex, East Antarctica: A preliminary report
- SHRIMP geochronology of a mylonite zone on Tonagh Island: characterisation of the last high-grade tectonothermal event in the Napier Complex, East Antarctica
- Electron microprobe dating of monazites from an ultrahigh-temperature granulite in Southern India : Implications for the timing of Gondwana assembly
- Magnetic microsperules in Permian and Triassic bedded chert from Southwest Japan
- Laser ablation ICP mass spectrometry for zircon U-Pb geochronology of metamorphosed granite from the Salem Block : Implication for Neoarchean crustal evolution in southern India
- Microstructurally controlled monazite chronology of ultrahigh-temperature granulites from southern India : Implications for the timing of Gondwana assembly
- Ultrahigh-temperature metamorphism of the Southern Marginal Zone of the Archean Limpopo Belt, South Africa
- "Ultrahigh density" carbonic fluids in ultrahigh-temperature crustal metamorphism
- Sapphirine and corundum bearing ultrahigh temperature rocks from the Palghat-Cauvery Shear System, southern India
- Laser ablation ICP mass spectrometry for zircon U-Pb geochronology of metamorphosed granite from the Salem Block: Implication for Neoarchean crustal evolution in southern India