Notes on petrography and rock-forming mineralogy (8) margarite-bearing metagabbro from the Iratsu mass in the Sanbagawa belt, central Shikoku.

Abstract

Margarite-bearing metagabbro was found from the iratsu epidote amphibolite mass in the Sanbagawa metamorphic belt. The sample is a metamorphosed anorthosite layer and consists of zoisite, paragonite, kyanite, margarite, chlorite, quartz and clay mineral (kaolinite or dickite). The unit cell parameter of margraite is as follows: a0=5.11 A, b0=8.79 A, c0=19.15 A. β=95.3°. Muscovite component in margarite is almost negligible, but (CaO=0.4-1.1 wt%) and Ca-poor (CaO=0.2-0.4 wt%) types. Within the constitutent of plagioclase in original anorthosite, and represent the equilibrium assemblage at the highest temperature stage during the Sanbagawa metamorphism. Margarite and Ca-rich paragonite were formed during the retrogressive metamorphism within the Sanbagawa stage.