徳島県穴吹川上流，木屋平の地質と地形

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タイトル別名
  • The geology and geomorphology in Koyadaira, upper stream of Anabukigawa area, East Shikoku, Japan
  • トクシマケン アナブキガワ ジョウリュウ コヤダイラ ノ チシツ ト チケイ

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The Mikabu and Chichibu belts in the Anabukigawa arre were studied with respect to their composition， boundaries and the relation with landslides. The main body of the Mikabu Greenstones is composed of the MORB-type tholeiite, and the Hawaiian and Polynesian-type alkaline basalts. The greenstones are dominated by dolerite intrusions into bedded-cherts. The coincidence of the chemical composition attributes the Taigo and Nakano greenstone bodies to the Mikabu Greenstones. The limestone phyllite of the Mt. Tsurugi was dated by the occurrence of Late Carboniferous conodonts. The co-occurrence of conodonts and crinoids suggests that the limestone originates from the tropical reef settings.The Fujinoike-dani Valley and the southern slope along the Anabukigawa River are characterized by the frequent occurrence of landslides and collupse of forest road-cuts. Because the faults，that cut the North Chichibu Belt，an d bounds from the Mikabu Greenstone Belt as well as the Kaminirogawa-Akuigawa Fault that obliquely cut them later，are concentrated in the Fujinoike-dani Valley and the southern slope along the Anabukigawa Riiver.The landslides are concentrated along the valley walls of the Anabukigawa River where Mikabu Greenstones and the Sanbagawa green and pelitic schists occur. The distribution of landslides in the area is controlled by the lithology (distribution of greenstone and schists)，the coincidence of their dipping with valley wall, the contents of swelling clay minerals in the weathered materials， and the changes in rock properties of pelitic schists due to weathering.

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