長崎県北西部の野島層群(中新統)中の酸性火砕流

概要

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In the northwestern part of Nagasaki Prefecture, Oya Formation, upper Miocene Series, is distributed with a trend of NEE-SWW direction. Acid volcanic tuff of about 20 to 35 meters thick, which is ever considered to be of the air-fall deposit, is contained in the uppermost part of this formation. We have investigated the mode of occurence, petrographic features and chemical compositions of this tuff. The results of this study can be summarized below. 1) The main part of the acid volcanic tuff, called "Kojimazaki tuff bed" may be the terrestrial pyroclastic flow, and the welding is therfore seen locally in the middle part. 2) Kojimazaki tuff bed is considered to be correlated to the rhyolitic tuff of Wakamatsu-jima and Nakadori-jima in the Goto Islands. 3) From the petrological point of view, this rhyolitic tuff may belong to the volcanic rock-series of Setouchi type, and at the same time be subject to the alteration of the "Green-tuff" type.
地学団体研究会の論文
1973-11-20