渡島大島火山の火山岩類と超苦鉄質・苦鉄質包有物

概要

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0shima-Oshima, an island of triple stratovolcano off the Japan Sea coast, southwest Hokkaido, is made up of lavas and pyroclastics, of which about 70 vol.% is alkalic olivine basalt and the rest is calcalkalic andesite. Most of the andesite contain abundant ultramafic and mafic inclusions such as dunite, wehrlite, clinopyroxenite and gabbro which show a typical cumulate texture. Some inclusions consist of olivine-clinopyroxene cumulates, clinopyroxene-hornblende-phlogopite-plagioclase intercumulattes, and interstitial glass with quenched plagioclase and ortho- & clinopyroxene needles. Occurrence of such inclusions suggests that the andesite magma has derived through fractional crystallization of olivine, clinopyroxene, hornblende and plagioclase from the alkalic olivine basalt magma probably under hydrous conditions in the crust. Mineralogy and major element chemistry of the rocks of Oshima-Oshima support this process.
特定非営利活動法人日本火山学会の論文
1977-12-15