Garnet-bearing pelitic schist from the Nago formation in the northern Okinawa Island

Garnet-bearing Shimanto pelitic schists occur in the Nago area of north-central Okinawa Island, Japan. The schists consist mainly of phengite, chlorite, quartz, albite, and epidote. They show narrow compositional banding, with bands composed of phengite + chlorite-rich and quartz-rich layers. The banded layers are deformed into isoclinal folds. The garnet occurs as euhedral grains with adjacent pressure shadows of mica and chlorite. The peak pressure-temperature conditions of metamorphism obtained from empirical garnet + muscovite + plagioclase thermobarometry are 4.1-4.6 kbar and 516-568°C, respectively. We propose that these conditions be used as reference values, because of the low almandine content of garnet. This is the first report of garnet-bearing pelitic schist from Okinawa Island.