愛媛県八幡浜市大島の変成岩の鉱物組み合せとK-Ar年代値
1990 年 85 巻 1 号 p. 19-26
詳細
1990 年 85 巻 1 号 p. 19-26
High-grade metamorphic rocks such as garnet amphibolite and garnet-biotite gneiss were found in Ohshima, Yawatahama city, western Shikoku. They occur in the Sanbagawa metamorphic belt and are in fault contact with greenstones of the pumpellyite-actinolite facies. Common occurrences of almandine garnet in the amphibolite and cummingtonite-quartz assemblage suggest that they belong to the amphibolite facies of the intermediate-pressure type metamorphism, distinct from the surrounding Sanbagawa metamorphic rocks. Two biotites and two amphiboles from the high-grade rocks have a narrow range of K-Ar age from 90 to 100 Ma. Although present occurrence of the high-grade rocks may be explained by thrusting over the Sanbagawa metamorphic rocks, there has been so far no report of a suitable candidate corresponding to the parental body of the high-grade metamorphic rocks.
