高原火山,富士山におけるマグマ混合機構 : 苦鉄質包有物による検討 Magma Mixing Mechanism of Fujiyama in Takahara Volcano, Northeast Japan : Evidence from the Mafic Inclusions
The Takahara volcano is a Quaternary stratovolcano located on the volcanic front in the southern part of the northeast Japan arc. Fujiyama is a dacitic lava dome in the northern part of the Takahara volcano, with dominant mafic inclusions that are andesitic in composition. A few phenocrysts lie across the boundary between host dacites and inclusions. Plagioclase and orthopyroxene phenocrysts in the host rocks and inclusions, respectively, have wide compositional variations; the whole-rock major and trace element compositions of these rocks yield linear data distributions. These results indicate that mixing between felsic and mafic magma occurred during the formation of the Fujiyama magma. The felsic end-member could be close in composition to the host dacite, whereas the mafic end-member is not similar to that of the eruptive products at the early stage of the Takahara volcano. It is suggested that the mafic inclusions were composed of andesitic magma formed by mixing in the chamber and then mingling in the conduit during ascent.
火山 59(2), 91-97, 2014