Calc alkali rocks derived from tholeiite magma in Hakone volcano

Abstract

The Hakone volcano is composed of island-arc type tholeiite magma, which is not dry but moderately hydrous. The moderately hydrous tholeiite magma can produce arc-tholeiite series and calc-alkali series through fractional crystallization in the magma reservoir under open-system condition and closed-system hydrous condition for water, respectively. The working hypothesis could be proposed by the change of magmatic temperature during fractionation. The magmatic temperature can be estimated by pyroxene-geothermometers.