Petrography of a discordant metabasite from Skallen, Lutzow-Holmbukta, East Antarctica

• Main Authors: Masaru Yoshida, Nobuyuki Aikawa
• Format: Report
• Language: English
• Published: Department of Geosciences, Faculty of Science, Osaka City University 1983
• Subjects: Antarctic; East Antarctica; Skallen; Antarc*; Antarctica; Enderby Land; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1474; http://id.nii.ac.jp/1291/00001474/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1474&item_no=1&attribute_id=18&file_no=1

A discordant metabasite from Skallen is an olivine tholeiite resembling petrochemically with some of the Proterozoic Amundsen dikes of Enderby Land. Field occurrence, mineral association, and microstructure including zoning structure of minerals are not incompatible with the polymetamorphic interpretation of the area presented by YOSHIDA et al. (submitted to Antarctic Earth Science, 1982), and indicate that the rock intruded in synchronous with or earlier than possibly the second and probably the first tectono-metamorphic event of YOSHIDA et al. Microprobe analyses and compositional zoning of constituent minerals of the metabasite are presented and some temperature and pressure values are calculated utilizing five different geothermometers and a geobarometer. Among calculated values, 693±3℃, 768±3℃, and 823±22℃ obtained by averaging temperatures after margin pairs of garnet-clinopyroxene (ELLIS and GREEN : Contrib. Mineral. Petrol., 71,13,1979) and garnet-biotite (THOMPSON : Am. J. Sci., 276,425,1976) geothermometers, after core pairs of two pyroxenes (WOOD and BANNO : Contrib. Mineral. Petrol., 42,109,1973) and garnet-clinopyroxene geothermometers, and averaging highest temperatures after core pairs of two pyroxenes and garnet-clinopyroxene geothermometers are considered possible to be explained either by the polymetamorphic or by the monometamorphic history of the discordant metabasite. It is stressed that the peak of a dominant metamorphism is considered to have reached the temperature much higher than 823℃ whichever the metamorphic history might have been.