Water content in arc basalts and its influence on volcanic activity: Case studies in Izu-Oshima, Miyakejima and Fuji volcanoes

Abstract

We studied water content in basalt magma from Izu-oshima, Miyakejima and Fuji volcanoes, based on petrology, OH in minerals, melt inclusions and experimental constrints on magma chambers, etc. We found that arc tholeiite basalt magma contains 3-5 wt% of water at crustal magma chamber depper than 10 km beneath these volcanoes. We show that changing lithology, fractionation trends and style of volcanic activity are largely controlled by the water content and the mode of degassing from the magma.