Clinopyroxenes in garnet-aegirine-augite schists from the Sambagawa metamorphic belt, Bizan district, eastern Shikoku, Japan

The Sambagawa metamorphic belt in the Bizan district consists mainly of pelitic schists, basic schists, and siliceous schists, along with minor garnet glaucophane schists.Siliceous schists containing garnet and clinopyroxene (garnet-aegirine-augite schists) are found within pelitic schists in both spotted and non-spotted schist zones.Garnet-aegirine-augite schists collected from the spotted schist zone consist mainly of quartz and phengite, with minor amounts of amphibole (ferroglaucophane, magnesioriebeckite, riebeckite, magnesiokatophorite, winchite, barroisite, ferrobarroisite), garnet, clinopyroxene (aegirine-augite, aegirine, omphacite; X Jd 0.08-0.37)and albite.Hematite, ilmenite, chlorite, epidote, calcite and titanite occur occasionally.Clinopyroxenes are found in two modes of occurrence: firstly, as inclusions in albite porphyroblasts (Cpx1), and secondly within the matrix (Cpx2).Most of the clinopyroxenes are zoned, with jadeite component-rich cores and jadeite-poor rims.This zoning represents decreasing jadeite component due to the decrease in pressure that occurred after the peak metamorphism.The jadeite component of Cpx1 is greater than that of Cpx2, suggesting that the composition of the clinopyroxenes was preserved within the albite porphyroblasts.