濃飛流紋岩と領家花崗岩との地質学的諸関係

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Nohi rhyolites, are presentative of the late Mesozoic acid volcanic rocks in the inner side of southwest Japan, have been hitherto considered as to be unconformably overlying, at their southern margin, on the erosion surface of the Ryoke granites. According to the writers detailed field observations in recent years, it was revealed that the Inagawa-Sumikawa granite, one of the so-called older Ryoke granites, was clearly intruding in to the rhyolites, and the latter was given extensive thermal effect resulting in the holocrystalline meta-volcanic rocks which had been erroneously called "quartz porphyries". A large amount of metamorphic minerals such as biotite, muscovite, hornblende, cordierite, andalusite, almandinous garnet, etc. were newly recrystalized from the rhyolites which were composed of originally, welded tuffs and their associated pyroclastic sediments. From the above-mentioned, the writers propose a new division of the Ryoke granites which is remarkably different from the customary one. Namely, Ryoke granites in a broader sense should be divided into Ryoke granites in a stricter sense and "post-Nohi" granites including Inagawa-Sumikawa granite. The writers' "post-Nohi" granites comprise massive or slightly schistose granites and granodiorites of various intrusion stage. They are widely distributed over the almost whole areas of the Ryoke metamorphic belt and, partly, over the non-metamorphic Paleozoic terrain called Mino belt. They are thought to be late Cretaceous in age, because the age of the Nohi rhyolites is evidently ascertained to be nearly late Cretaceous, and both the K-Ar and Rb-Sr datings on the minerals of the granites result in 60-70 million years in most cases. On the other hand, Ryoke granites in a stricter sense, comprise mainly gneissic granodiorites and quartz diorites. Distribution of the granites are limited with in the area of the higher metamorphic grade of the Ryoke belt, namely, banded gneiss zone characterized by the occurrence of sillimanite from pelitic rocks. There are several localities where the granites are found to be intruded or captured by "post-Nohi" granites. It is impossible, however, to make clear the mutual geologic relations between the granites and the Nohi rhyolites, because the both are essentially different in distridution. Detailed isotopic age investigation on the Ryoke granites in a stricter sense is hoped to be carried out and to contribute to the chronology of the Ryoke plutonometamorphism.
日本地質学会の論文
1969-01-31

濃飛流紋岩と領家花崗岩との地質学的諸関係

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