関東平野西縁の地質
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概要
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Structural features of transitional region from the northeastern Kanto Mountains to the Kanto Plain is discussed in this paper. Along the northern margin of the Kanto Mountains, Namekawa zone, a characteristic zone of NW-SE trend, about 5 km wide, is developed. The Namekawa zone is the boundary zone between the Tertiary area of the Kanto plain on the north, and the Sanbagawa terrane of the Kanto mountains on the south. The Namekawa zone is characterized by the Middle Miocene sediments with slump structure sand with complicated folds, and by the gneiss and granite assigned probably to the rocks of the Ryoke terrane. The northern boundary of the Namekawa zone is represented by the Oya fault (defined in this paper), and the southern by the Naranashi fault (KOKATSU et al., 1970), which is probably equivalent to the Median Tectonic Line of Southwest Japan. TheSanbagawa terrane of the Kanto Mountains is bordered on the north by the Namekawa zone in this region, and by the Shimonita tectonic zone (ARAI et al., 1966) to the west. Therefore, they may be jointly called Shimonita-Namekawa zone. In the Early Miocene the sediments were formed mainly in the Sanbagawa terrane, and the Namekawa zone might have been the area of non-deposition. In the Middle Miocene the Namekawa zone was subsided rapidly. In the Late Miocene the zone was uplifted, and the sediments of this epoch were formed on the outside of the zone. The Iwatono Hills is situated on the east of the Kanto Mountains, and composed of sediments of Late Miocene and Pliocene. The Iwatono Hills is bordered on the west and the east by the faults of N-S trend. The fault of western margin of the Hills is a part of the Hachioji Tectonic Line, and that of the eastern margin is a southern extension of the Matsuyama fault (TAKEI et al., 1976). The eastern part of the Hills is tilted to west-southwest, with the slight synclinal structure of the Upper Miocene in the western margin. The tilting occured after the deposition of the Upper Miocene and before the deposition of the Pliocene.
- 日本地質学会の論文
- 1981-03-30