Decompressional microstructure from garnet-bearing mafic granulite in Yanai district, Ryoke belt, Southwest Japan

Abstract

Newly found garnet-bearing mafic granulite in Yanai district, Ryoke belt occurs as blocks in gneissose tonalite. This granulite consists mainly of brown hornblende, orthopyroxene and plagioclase, with trace amounts of garnet, biotite and quartz. Garnet porphyroblast up to 3 cm in diameter is locally contained, and is surrounded by orthopyroxene and plagioclase symplectites that coexist with quartz. On the basis of microstructure and mineral assemblage in the garnet-bearing mafic granulite, it reveals that the reaction of garnet + quartz→orthopyroxene + plagioclase occurred at a decompressional process under the granulite facies condition.