四国黒瀬川構造帯の岡成層群酸性火山岩

概要

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Acid volcanic rocks of the Okanaro Formation in the Kurosegawa Tectonic Zone, Shikoku, are petrographically classified into two major groups of rhyolite and rhyolitic tuff. The latter includes vitro-clastic tuffs and vitric-crystal tuffs. Relic textures and a part of relic crystals of the original volcanic and pyroclastic rocks are fairly well preserved. However, the rocks have mostly suffered weak metamorphic recrystallization under the conditions of the prehnite-pumpellyite facies. Chemical analyses reveal that some rocks, mostly rhyolites, have been enriched with soda due to albitization and others, largely tuffs, have become rich in potash according to kali-feldspathization. These chemical changes have probably occurred in connection with the low-temperature metamorphism which affected the rocks.
国立科学博物館の論文
1976-10-29