三波川帯,八幡浜地域のざくろ石一単斜輝石角閃岩類

Abstract

Garnet-clinopyroxene amphibolites from the Kawamai tectonic mass emplaced in the Sanbagawa metamorphic terrain of the Yawatahama district, southwestern Shikoku have been studied chemically. The amphibolites are characterized by the assemblage brown hornblende-garnet-clinopyroxene-calcic plagioclase indicating, at least, the amphibolite facies.Their bulk rock compositions are always undersaturated with silica. The ferromagnesian minerals are saute with appreciable amounts of acmite and Tschermak's components, Ca-rich almandine and ferroan pargasite. From chemical comparison of clinopyroxene and of hornblende the formation temperature seems to be higher in the Kawamai amphibolites than in the Iratsu amphibolites. The partition coefficient of Fe and Mg between garnet and clinopyroxene suggests that the Kawamai amphibolites equilibrated at a temperature higher than or similar to that of the Higashi-Akaishi-yama garnet clinopyroxenites.It can be concluded that the Kawamai mass suffered the Sanbagawa metamorphism corresponding to the amphibolite facies of which Ps-T conditions were similar to those of the Higashi-Akaishi-yama mass, but prevailing PH2O must have been different between the two. Retrogressive reactions have been caused by the subsequent uplift of the Kawamai mass during the Sanbagawa metamorphism.