Sulfur supplies of arc volcanoes from frontal to back-arc-sulfur contents of melt inclusions in phenocrysts

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Our research project revealed that subduction related magmas of island arc volcanoes have high sulfur concentrations. Mafic magmas are expected to supply large amounts of sulfur to the volcanic magma system, and the sulfur is released during eruptions. We investigated the characteristics of major components and estimate sulfur supplies in the magma systems of volcanics from the volcanic front to back-arc, based on melt inclusion studies.1)we performed microprobe analyses of sulfur as well as major components of melt inclusions trapped in olivine phenocrysts from many volcanoes along the volcanic front from southwest Hokkaido through Tohoku to Chubu areas. Mafic magmas injected into the felsic chamber beneath the volcanoes is indicated to be hidrous and have large sulfur concentration. The mafic magmas were vesiculated before the melt entrapment in olivine phenocrysts.2)In the back-arc areas, on the other hand, melt inclusions in olivine phenocrysts have relatively low sulfur concentration, and phenocrysts (olivine and pyroxene) trapped high-K_2O melt inclusions.3)We performed microprobe analysis for sulfur, FTIR analysis for H2O, determine Sulfur-Xray peak shift of the melt inclusions trapped in olivine phenocrysts, and tried to develop some methods in the melt inclusion study.