[SCG60-P05] Generation and evolution processes of rhyolitic magma in Niijima volcano, Izu-volcanic arc, Japan: petrological and geochemical constaints
Keywords:Niijima volcano, High silica rhyolite, Izu volcanic arc, Cummingtonite
Mineral assemblages particularly with cummingtonite and without clinopyroxene, and high SiO2 and K2O contents of rhyolites suggest that the magmas were produced under low temperature (< 800ºC) and pressure (< 3kb), and hydrous conditions. The major and trace element characteristics indicates prominent fractionation of amphiboles and plagioclase from the parental magmas, and this is supported by tonalitic cumulate xenoliths found in the rhyolitic lavas and pyroclastics (Arakawa et al., 2017). The primitive magma is assumed to have been generated by partial melting of middle crust rather than the mafic lower crust. In comparison with the other rhyolites in volcanic front and rear arc regions in northern Izu-Bonin arc, the Niijima rhyolites show distinct features from the others, possibly representing the differences in magma source, and generation and differentiation processes of silicic magmas.