Inferred ultrahigh-temperature metamorphism of amphibolitized olivine granulite from the Sør Rondane Mountains, East Antarctica |
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| Authors: | Nobuhiko Nakano Yasuhito Osanai Sotaro Baba Tatsuro Adachi Tomokazu Hokada Tsuyoshi Toyoshima |
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| Institution: | aDivision of Earth Sciences, Faculty of Social and Cultural Studies, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan;bDepartment of Natural Environment, University of the Ryukyus, Okinawa 903-0213, Japan;cNational Institute of Polar Research, Tokyo 190-8518, Japan;dGraduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan |
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| Abstract: | This paper reports the first evidence of ultrahigh-temperature (UHT) metamorphism from the Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, which is evident as orthopyroxene + spinel symplectite in an amphibolitized mafic granulite. The granulite consists of olivine, orthopyroxene, clinopyroxene, pargasitic amphibole, plagioclase, and ilmenite, and it possesses a within-plate alkali basalt signature. The local bulk chemical composition of symplectite, major and trace element compositions, and thermodynamic calculations for the symplectite, suggest the presence of garnet at the high-pressure stage and that the symplectite formed from garnet, olivine, and primary orthopyroxene by decompression from more than 12 kbar at 1000 °C. The granulite records a subsequent amphibolite-facies overprint (<700 °C at <6 kbar) that involved the chemical re-equilibration of several phases. The obtained pressure–temperature (P–T) conditions and P–T path are different from the UHT metamorphism from the Schirmacher Hills, central Dronning Maud Land, which is considered to have occurred in a back-arc tectonic setting. The relatively high-P conditions and the decompression path reconstructed in the present study are similar to those reported for southern India, Sri Lanka, and part of northeastern Mozambique, possibly reflecting continental thickening and exhumation during the main collision event between East and West Gondwana. |
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| Keywords: | Orthopyroxene + spinel symplectite Ultrahigh-temperature metamorphism Sø r Rondane Mountains East African&ndash Antarctic Orogen |
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