Sapphirine + quartz association in garnet: implication for ultrahigh-temperature metamorphism at Rundvågshetta, Lützow-Holm Complex, East Antarctica
Yasutaka Yoshimura, Yoichi Motoyoshi, Tomoharu Miyamoto, 2008. "Sapphirine + quartz association in garnet: implication for ultrahigh-temperature metamorphism at Rundvågshetta, Lützow-Holm Complex, East Antarctica", Geodynamic Evolution of East Antarctica: A Key to the East–West Gondwana Connection, M. Satish-Kumar, Y. Motoyoshi, Y. Osanai, Y. Hiroi, K. Shiraishi
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We report the occurrence of sapphirine+quartz association within garnet porphyroblast in the garnet–orthopyroxene–sillimanite granulite (Grt–Opx–Sill granulite) from Rundvågshetta in the Lützow-Holm Complex, East Antarctica. The granulites in the study area show a characteristic mineral assemblage consisting of orthopyroxene+sillimanite+quartz. The presence of sapphirine and quartz inclusions within garnet in the sapphirine-bearing Grt–Opx–Sill granulite suggests that metamorphic conditions changed from the stability field of orthopyroxene+sillimanite+quartz to that of sapphirine+quartz during the garnet growth. Peak metamorphic temperature conditions of about 1000–1100 °C are obtained by ternary feldspar thermometry for these granulites. Similar temperatures were also estimated from the Al-in-orthopyroxene geothermometer. The granulites are also characterized by coarse-grained garnet, being partly surrounded by a fine-grained symplectite composed of orthopyroxene and cordierite, whereas sapphirine+cordierite symplectitic intergrowth occurs in the matrix. These textures imply that the area underwent isothermal decompression subsequent to ultrahigh-temperature metamorphism. The sapphirine-bearing Grt–Opx–Sill granulite is likely to be the restitic product of partial melting and shows signs of segregation and movement of melt.
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Geodynamic Evolution of East Antarctica: A Key to the East–West Gondwana Connection
Geological correlations of East Antarctica with adjoining continents have been puzzling geologists ever since the concept of a Gondwana supercontinent surfaced. Despite the paucity of outcrops because of ice cover, difficulty of access and extreme weather, the past 50 years of Japanese Antarctic Research Expeditions (JARE) has successfully revealed vital elements of the geology of East Antarctica. This volume presents reviews and new research from localities across East Antarctica, especially from Dronning Maud Land to Enderby Land, where the geological record preserves a history that spans the Archaean and Proterozoic. The reviews include extensive bibliographies of results obtained by geologists who participated in the JARE. Comprehensive geological, petrological and geochemical studies, form a platform for future research on the formation and dispersion of Rodinia in the Mesoproterozoic and subsequent assembly of Gondwana in the Neoproterozoic to Early Palaeozoic.