Ultrahigh temperature sapphirine-osumilite and sapphirine-quartz granulites from Bunt Island in the Napier Complex, East Antarctica -Reconnaissance estimation of P-T evolution -

• Main Authors: Yasuhito Osanai, Tsuyoshi Toyoshima, Masaaki Owada, Toshiaki Tsunogae, Tomokazu Hokada, Warwick A. Crowe, Isao Kusachi
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Okayama University/Department of Geology, Niigata University/Department of Earth Sciences, Yamaguchi University/Institute of Geoscience, University of Tsukuba/National Institute of Polar Research/Department of Geology and Geophysics, University of Western Australia/Department of Earth Sciences, Okayama University 2001
• Subjects: sapphirine; osumilite; P-T path; Bunt Island; Napier Complex; Antarctic; East Antarctica; Napier; Bunt; Amundsen Bay; Antarc*; Antarctica; Enderby Land; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3082; http://id.nii.ac.jp/1291/00003082/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3082&item_no=1&attribute_id=18&file_no=1

The summer party of the 39th Japanese Antarctic Research Expedition (1997-1998) carried out geological field work on Bunt Island at the southeastern end of Amundsen Bay, Enderby Land, which is in the highest-grade metamorphic region in the Napier Complex. The island is underlain by various kinds of ultrahigh-temperature (UHT) metamorphic rocks including osumilite-bearing aluminous sapphirine-garnet-orthopyroxene granulite and quartz-predominant sapphirine-garnet-sillimanite gneiss containing the assemblage sapphirine-quartz. Osumilite-bearing aluminous granulite is silica-undersaturated, aluminous and magnesian chromium-rich chemical affinity. Osumilite-bearing granulite from Bunt Island could be formed through the mixing of clayey materials or other felsic components derived from felsic igneous rocks with a relatively high proportion of mafic to ultramafic detritus in the sedimentary precursor. The chemical mixing could have taken place during c. 3.2 and c. 2.5 Ga. P-T estimation for osumilite-bearing granulite and related sapphirine-quartz gneiss indicates ultrahigh-temperature condition (～1100℃, ～1100 Mpa) as well as other high-grade rocks from the Napier Complex, but the rocks from Bunt Island clearly show isothermal decompression in part of the clockwise P-T evolutional process.