Quantification of H2O concentration in arc basaltic melts using H concentration in nominally anhydrous minerals

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Nominally anhydrous minerals in igneous rocks contain trace amounts of hydrogen as impurities, which can be used as an indicator of dissolved H2O concentration in coexisting melt and behavior of H2O during degassing of magmas. In this project , correlations between hydrogen concentration in plagioclase and H2O concentration in coexisting basaltic melt was investigated based on melting experiments on hydrous basalts, which suggests that island arc basaltic magmas beneath frontal-arc volcanoes is H2O-rich. In order to confirm this view, geochemical variation of aphyric volcanic rocks collected from the Izu-Oshima volcano in the Izu arc for the past 40,000 years was reviewed to examine conditions at which major crystallization differentiation have taken place. The consistency between these two independent studies was confirmed.