Sulfar and chlorine yield from island arc.rolcano ; Volatiles in melt inclusion of phenocrysts.

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Melt inclusion studies of Asama volcano have found mafic melts trapped in olivine, rare phenocrysts derived from the mafic magma, and provided an insight that basaltic liquid played an important role as the mafic endmember of the mixed magma system. Olivine phenocrysts contain mafic melt inclusions of basaltic to andesitic compositions. The mafic melt inclusions have very large sulfur concentration (0.15-0.34 wt% S). Measured wavelength shifts of sulfur X-rays for the basaltic melt inclusions indicate that the dominant sulfur-bearing species is SO_4^<2->, with a correspondingly high sulfur solubility. It appears probable that a relatively oxidized basaltic melt at the subduction zone could have a large concentration of sulfur, and therefore, subduction-related arc volcanisms potentially supply a large amount of mantle-derived sulfur to the earth's surface.