(英) Geological structures of the Northern Chichibu Terrain of the Sasagatani Area, Central Shikoku (日) 四国中央部笹ヶ谷地域における秩父帯北帯の地質構造
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(英) The Sasagatani fault in central Shikoku was considered to be a tectonic boundary between the Sambagawa high-P/T metamorphic belt and the Chichibu non-high-P/T belt. Metamorphic minerals of the greenstones around the Sasagatani fault are examined. Alkali amphibole, alkali pyroxene, actinolite, stilpnomelane and pumpellyite are found not only on the north side of the fault, but also on the south side. Strata around the Sasagatani fault have undergone the pumpellyite-actinolite facies metamorphism. Thus, the Sasagatani fault is not an upper boundary fault of the Sambagawa metamorphic rocks. The Nanokawa thrust occurs in the Jurassic accretionary complexes of the Northern Chichibu Terrain in the Sasagatani Area. The greenstones of the hanging wall of the thrust have undergone the pumpellyite-actinolite facies metamorphism, whereas those of the footwall have undergone the prehnite-pumpellyite facies metamorphism. The Nanokawa thrust is a large overthrust, which has a different metamorphic grade between the hanging wall and footwall. The thrust is probably a southern boundary of the Jurassic accretionary deposits which have undergone the Sambagawa metamorphism. (日) 四国中央部,笹ヶ谷地域における秩父北帯の地質構造が明らかにされた.三波川変成岩類の上限の正断層とされた笹ヶ谷断層の北側・南側で緑色岩類中の変成鉱物を調べたところ,同断層とされた位置の北側だけでなく南側からもアルカリ角閃石の産出が確認された.笹ヶ谷断層は断層が存在するとしても,変成度のギャップをもたらすものではなく,大規模な断層ではないことが明らかになった.なお,変成度のギャップをもたらす大規模な断層として,さらに南側は名野川衝上断層の存在が推定された.
Akihiro Murata, Ryosuke YAMAZAKIandHirokazu MAEKAWA : Geological structures of the Northern Chichibu Terrain of the Sasagatani Area, Central Shikoku, Natural Science Research, Faculty of Integrated Arts and Sciences, The University of Tokushima, Vol.23, 65-76, 2009.
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