H2O-rich island arc basalt magma at volcanic front inferred from analyses of hydrogen in Ca-rich plagioclase

Abstract

Trace amounts of water in Ca-rich plagioclase from island arc basalt were analyzed using polarized infrared spectroscopy. Water contents in plagioclase varied from 50 to 300 ppm H₂O, which correspond to 1.5 to 6.0 wt.% H₂O in the coexisting melt. We present a polybaric degassing model from H2O-saturated basaltic melt to explain the variation in water content of the Ca-rich plagioclase in island arc basalt beneath the volcanic front.