岡山県大佐地域の三郡変成帯中の藍閃石とフェロ藍閃石

The Sangun metamorphic terrane, which is situated in the inner side of southwest Japan, is one of the glaucophanitic metamorphic terranes of high-pressure intermediate type in late Paleozoic−early Mesozoic. It is characterized by widespread occurrences of pumpellyite-bearing assemblages and sodic amphibole-bearing assemblages in mafic schists. Sodic amphibole in the Sangun terrane is mainly crossite− magnesioriebeckite with b = Z (Hashimoto, 1968a & b; Nishimura, 1971; Okamura et al., 1975; Kobayashi, 1979) whereas glaucophane with b = Y shows relatively minor occurrence as described from Zone II in the Katsuyama district (Hashimoto, 1968a) and Goutsu ( = Gozu) district (Sengan et al., 1983). As suggested by Hashimoto (1968a, page 140), composition of sodic amphibole may reflect different physical conditions of metamorphism. Chemical composition of sodic amphibole is important for fully understanding the physical conditions of the Sangun metamorphism. The author briefiy descibes glaucophane and ferroglaucophane, the latter of which is first reported in the Sangun terrane, in the Oosa district.