| Abstract |
The Yatsushiro gneisses occur as squeezed-out blocks, highly contorted and sheared, in the Kurosegawa Zone, in the Outer Zone of Southwest Japan. The gneisses consist of amphibolite, mica gneiss, and ...quartz gneiss, probably of Precambrian age. The host rock of the garnet reported in this paper is garnet-clinopyroxene-andesine gneiss, in the amphibolite body. It is inferred to be kept out of the amphibolitization by which the amphibolite was formed. The sample was picked up at Oshino, Sakamoto-mura Yatsushiro-gun, Kumamoto Prefecture. The garnet of the garnet-clinopyroxene-andesine gneiss is a large idiomorphic porphyroblast, about 1c m in diameter. Its physical properties are as follows: brownish red in colour; 1.751 in refractive index; 3.879 in specific gravity; 11.5817 A in unit cell edge. Its chemical composition is characterized by pyrope molecule of about 40 %; almandine 39 % ; andradite 12 %. The chemical composition of the garnet indicates that the host rock had been metamorphosed in grade of granulite or eclogite facies before the amphibolite facies was formed. The fact is remarkably important in geohistory of the Japanese Islands.show more
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