津川地域の中新世酸性火山岩

概要

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Miocene voluminous acid volcanic rocks are widely distributed in the Tsugawa area, Northeast Japan. They are rhyolitic and perlitic lava flows and their pyroclastics erupted in submarine condition. Mineral composition of them is characterized by Fe-rich pyroxene phenocryst in this area, synchronous basaltic hyaloclastite and tuff breccia are intercalated in acid pyroclastics. Accordingly, this area belongs to the zone of bimodal volcanism. In this paper, occurrence, petrography and chemical composition of acid volcanics are described. EPMA data of phenocryst minerals are also given. Perlite is closely associated with rhyolite occurring as alternating layers in various scale. Difference of chemical composition between perlite and rhyolite seems to be primary. It is likely that they were separated in magma reservoir by liquid immiscibility and were elongated in transport process to form banding.
日本地質学会の論文
1984-11-30