東北本州弧, 磐司岩火山岩類の地質と岩石

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The Banji-iwa volcanic rocks (BVR), spread across the central mountainous backbone of the Northeast Honshu arc, form a volcanic complex comprising four composite volcanoes and more than fourteen monogenetic centres. Volcanic activity of the BVR began in the late Pliocene and can be classified into three eruptive stages: Stage I, II and III. Stage I is characterized by the formation of subaqueous andesitic to dacitic lava domes, lava flows, volcaniclastic rocks and feeder dikes. The volcanic products of Stage II largely consist of subaqueous andesitic and dacitic lava flows, volcaniclastic rocks, and feeder dikes. In Stage III, four subaerial composite volcanoes (Senohara-yama, Yamagata Kamuro-dake, Sendai Kamuro-dake and Daito-dake), one dacitic lava dome (Takakura-yama) and three andesitic lava domes (Sanpoukura-san, Koazuma-dake and Minamiomoshiro-yama) were formed. The BVR consists of two-pyroxene andesite and dacite with small amounts of olivine-bearing two-pyroxene andesite. The lavas in the eruptives of Stage I volcanoes include the hypersthenic rock series; in contrast, the hypersthenic rock series and the pigeonitic rock series are found to coexist in the eruptives of Stage II and III volcanoes. Lavas of the BVR are distinctively poor in K2O and Rb as compared to those of the Quaternary Sekiryo volcanic rocks.
日本鉱物科学会の論文
2006-03-20