Fluid inclusions in an osumilite-bearing granulite from Bunt Island in the Archean Napier Complex, East Antarctica: implications for a decompressional P-T path?

• Main Authors: Toshiaki Tsunogae, M. Santosh, Yasuhito Osanai, Masaaki Owada, Tsuyoshi Toyoshima, Tomokazu Hokada, Warwick A. Crowe
• Format: Report
• Language: English
• Published: Department of Geology, Rand Afrikaans University/Department of Natural Environmental Science, Kochi University/Department of Earth Sciences, Okayama University/Department of Earth Sciences, Yamaguchi University/Graduate School of Science and Technology, Niigata University/National Institute of Polar Research/Department of Geology and Geophysics, University of Western Australia 2003
• Subjects: Carbonic fluid inclusion; ultrahigh-temperature granulite; Bunt Island; Archean Napier Complex; East Antarctica; Napier; Bunt; Antarc*; Antarctica; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3122; http://id.nii.ac.jp/1291/00003122/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3122&item_no=1&attribute_id=18&file_no=1

We report high-density CO_2-rich fluid inclusions in garnet,orthopyroxene,and quartz from an osumilite-bearing aluminous granulite from Bunt Island of the Archean Napier Complex,East Antarctica.The melting temperatures of fluids lie in the range of -56.8 to -57.8゜C being close to the triple point for pure CO_2 (-56.6゜C ). Homogenization of the CO_2,-rich fluids into the liquid phase occurs at temperatures in the range of -35.4 to 24.7゜C. This translates into CO_2 densities in the range of 0.788-1.084g/cm^3 .The estimated CO_2 ,isochore for high-density inclusions in garnet intersects the P-T trajectory of Bunt Island at around 10 kbar at 1050゜C, which corresponds to the peak metamorphic conditions of the region derived from mineral phase equilibria.We therefore infer that CO_2 ,was the dominant fluid species present during the ultrahigh-temperature metamorphism in Bunt Island.CO_2 inclusions with lower density occurring in quartz and garnet provide isochores that intersect the P-T path at <7 kbar and <950゜C indicating density reversal of originally high-density inclusions along a decompressional exhumation path of the ultrahigh-temperature rocks in the Bunt Island.