阿武隈変成帯の造構作用  [in Japanese] Tectonism in the Abukuma metamorphic belt  [in Japanese]

The basement complex of Northeast Japan cosists of Abukuma belt, Matsugadaira-Motai belt, South Kitakami belt, North Kitakami belt and Taro belt. The South Kitakami belt appears to have been a part of continent placed near Gondwana during Silurian to early Carboniferous, though it was later rifted and drifted from the continent (SAITO & HASHIMOTO, 1982). The Matsugadaira Motai belt is a glaucophanitic metamorphic belt of middle Silurianto middle Devonian developed along the western margin of the South Kitakami belt. The original rocks of metamorphics of the Abukuma belt consist of two components: One is an accretion prism (=Gosaishyo-Takanuki metamorphics and Nishidohira metamorphics) of late Palaeozoic developed along the western margin of the Matsugadaira-Motai belt and the other is a nappe (=Hitachi metamorphics) of rocks of the South Kitakami belt. In the Hitachi district located at the southern margin of the Abukuma belt the nappe overlies the accretion prism. It has been suggested that the tectonism responsible for the formation of the nappe of the South Kitakami belt is due to collision of a part of the Asian continent and the continental fragment containing the Matsugadaira-Motai belt and South Kitakami belt, and that the metamorphism of kyanite-sillimanite type in the Abukuma belt occurred during the collision. After the metamorphism of kyanite-sillimanite type, the Abukuma belt, as well as the south Kitakami and Matsugadaira-Motai belts, collapsed developing shear zones associated with intrusion of serpentinite bodies and metamorphism of greenschist facies. The collapsing of these belts appears to be related to the collision and to the appearance of the subduction zone along the eastern margin of the South Kitakami belt during Jurassic age, which is associated with the formation of the accretion prisms of the North Kitakami and Taro belts. The upright folding of the rocks of the terrain from the Abukuma belt to the Taro belt occurred during the latest jurassic to the earliest Cretaceous age. The metamorphism of andalusite-sillimanite type in the Abukuma belt occurred during the upright folding, associated with the intrusion of the granite bodies (e.g. Samegawa granite), though most of them in the terrain from the Abukuma belt to the Taro belt intruded immediately after the upright folding.