三郡・三波川・領家各変成帯相互の関係

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In southwestern Japan, three metamorphic belts, the Sangun, the Sanbagawa and the Ryoke ones, are located with parallelism. Of these, the Sangun and the Sanbagawa metamorphic belts are considered to be two branches of one and the same metamorphic belt and to be conjugated in northern Kyushu, judging from the geologic age of their original sediments, their metamorphic ages, the type of their metamorphisms and their distributions. This metamorphic belt is poiyaxial with northern and the southern synclinoria. At present, the former is occupied by the unmetamorphosed Paleozoic sediments including the Akiyoshidai and the Taisyakukyo limestone formations and the latter by the Ryoke metamorphic and granitic rocks. The differences in petrological characters between these two branches depend probably upon the scale of geosynclinal subsidence. It proceeded with far larger scale in the Sanbagawa belt than in the Sangun one. Consequently, the Sangun metamorphic belt consists mainly of the rocks of the green schist fades, whereas the Sanbagawa belt is characterized by the glaucophanitic metamorphism. Moreover, even in the Sanbagawa belt, the subsiding movement in the area to the west of central Kii peninsula shows a distinct difference from that of the eastern part. In the western part, the Sanbagawa belt was differentiated into the intermediate upheaval zone and its both-sided subsiding zones. The subsidence was conspicuous in the northern subsiding zone. On the other hand, in the eastern part of the belt including the eastern Kii peninsula, the subsidence proceeded uniformly. Consequently, in the eastern part of the Sanbagawa metamorphic belt, the distinct lawsonite and jadeite zones were formed, whereas in the western part, they are totally defect. Moreover, the northern subsiding zone in the western part consists of the rocks of the glaucophane schist and the epidoteamphibolite facies, whereas the intermediate upheaval and the southern subsiding zones are composed of the rocks of the green schist facies. After the middle Cretaceous age, severe acid plutonism attacked the Japanese Islands. Its forerunner occupied the unmetamorphosed part of the southern synclinorium of the older metamorphic belt mentioned above. This is the Ryoke metamorphic belt. The Ryoke metamorphism owes its main agency to the upheaval of the isogeothermal surface due to this plutonism.
地学団体研究会の論文
1962-11-30

著者

端山好和
地学団体研究会東京支部

三郡・三波川・領家各変成帯相互の関係

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