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

火成岩中名义上无水的矿物中含有微量的氢杂质，可作为共存熔体中溶解H2O浓度和岩浆脱气过程中H2O行为的指示剂。本项目在含水玄武岩熔融实验的基础上，研究了斜长石中氢浓度与共存玄武岩熔体中H2O浓度之间的相关性，表明弧前火山下岛弧玄武岩岩浆是富H2O的。为了证实这一观点，我们回顾了从伊豆弧伊豆大岛火山采集的近4万年来的无定形火山岩的地球化学变化，以考察发生主要结晶分异的条件。这两项独立研究之间的一致性得到证实。

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.