Amphiboles from the garnet glaucophane schists in the Bizan area, Sambagawa metamorphic belt, eastern Shikoku, Japan

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The Sambagawa metamorphic belt in the Bizan area consists mainly of pelitic schists, basic schists, and siliceous schists, along with minor garnet glaucophane schists. Garnet glaucophane schists consist mainly of garnet and amphibole (glaucophane, ferroglaucophane, barroisite, katophorite and taramite), with minor amounts of epidote, phengite, paragonite, chlorite, albite, titanite, and quartz. Clinopyroxene (jadeite-omphacite), chloritoid, rutile, ilmenite, calcite, K-feldspar, zircon occur occasionally. Amphiboles have five modes of occurrence. Amphiboles inclusions in porphyroblastic garnets are sodic and sodic calcic amphiboles (Amp1; ferroglaucophane, glaucophane, ferrobarroisite, barroisite, taramite). Taramitic amphiboles occur restrictedly in the cores of the porphyroblastic garnets. Amphibole inclusions in the rim of the garnets are zoned, with barroisite core and glaucophane rim. Amphibole inclusions in albite (Amp2), epidote (Amp3) and chlorite (Amp4) are ferroglaucophane in composition. Ferroglaucophane and glaucophane occur in the matrix (Amp5), and some of them are zoned from glaucophane core to barroisite rim. The diversity of the modes of occurrence and chemical compositions of the amphiboles reflect three metamorphic events of the garnet glaucophane schists in the Bizan area. A precursor metamorphic event is represented by the taramitic amphibole inclusions in the core of the porphyroblastic garnet. Schistosity-forming amphiboles (ferroglaucophane, glaucophane), amphiboles inclusions in the porphyroblastic garnets (ferroglaucophane, glaucophane, ferrobarroisite, barroisite) and amphibols included in albite, epidote and chlorite (ferroglaucophane) are representative of the prograde to the peak metamorphism of eclogitic metamorphic event. Barroisite rim of zoned amphiboles is probably developed during the epidote-amphibolite metamorphic event.