<国立科博専報>東北地方脊梁山脈の造構運動と火成作用

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The Backbone Range, a site of the initial volcanism, played an important role in the geologic development of the Green Tuff Region in Northeast Japan. Birth of the Creen Tuff Region was preceeded by acidic igneous activities through the Late Cretaceous to Paleogene. Thinning and stretching of the thick crust formed by the Oshima orogenic movement were succeeded through this acidic igneous activities. Separation of the Japanese Islands from the Asiatic Continent started simultaneously with this activities. The stage of thinning and streching of crust (120-22.5Ma), here proposed, is also intimately related to the opening of the Sea of Japan, althougn the area did not submerged yet under the sea. Close to the terminal stage of the thinning and stretching of crust, the initial volcanism of intermediate nature commenced in the Green Tuff Region, and was followed by a rapid subsidence of the area parallel to the Backbone Range of today. The pre-rifting stage (22.5-15Ma) is represented by the time of the initial volcanism and of acumulation of thick sequence of green tuff in and around the Backbone Range. Then, it was followed again by maximum subsidence indicated by a thick accumulation of monotonous siliceous or hard shale accompanied with extrusion of basalt and dolerite in the region of the Dewa hill. Extrusion of basalt and dolerite marks the rifting stage (15-10Ma) of eventually thinned and stretched underlying crust. Deformation of the Green Tuff Region took place after the Late Miocene differentiation stage under the compressional stress condition. Uplift of the Backbone range was completed through the dacitic volcanic activities accompanied with caldron collapse through Late Miocene to Plio-Pleistocene. Late Pleistocene to Recent neo-volcanisms genetically related with subduction of the Pacific plate were superimposed the Backbone Range formed during Neogene time.
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<国立科博専報>東北地方脊梁山脈の造構運動と火成作用

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