GEOLOGIC STRUCTURE AND METAMORPHIC ZONING OF THE NORTHERN EXTREMITY OF THE SANBAGAWA METAMORPHIC TERRAIN IN THE KANTO MOUNTAINS

Abstract

The studies on the geologic structure and the metamorphic zoning of the crystalline schists which expose in the northern extremity of the Sanbagawa metamorphic terrain of the Kanto Mountains, central Japan have been carried out by the present writers. The geologic structure in this area is gentle, being usually flat without large-scale folding. On the basis of the stability relation of metamorphic minerals, this district may be divided into three zones. Zone I is characterized by the occurrence of pumpellyite and alkaliamphibole. In zone II, pumpellyite and alkali-amphibole are not stable and “green biotite” appears. Common hornblende and “brown biotite” are observed in zone III. In term of mineral facies concept, zones I, II and III correspond to the glaucophane schist facies (lower pressure side), the green schist facies and the epidote-amphibolite facies, respectively. The metamorphism of zones I, II and III is progressive one, and the metamorphic grade increases southwards. Consequently, the present writers think the existence of the center line which attains to the highest temperature of the Sanbagawa metamorphism in the Kanto mountains.