"早池峰構造帯"研究の現状と課題

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The "Hayachine Tectonic Belt" borders the Southern Kitakami and Northern Kitakami Massifs, and is characterized by widespread basic to ultrabasic rocks named the Hayachine Complex. In the central part, i. e. Hayachinesan-Oguni district, the Hayachine Complex consists of the Nakadake Serpentinite, Kagura Complex and Koguro Formation, in ascending order. The Nakadake Serpentinite is composed of serpentinite and serpentinized ultrabasic rocks, and the Kagura Complex is a complex of trondhjernite, dolerite, gabbro and ultrabasic rocks. The Koguro Formation is composed mainly of dolerite and basalt and is overlain by thick terrigenous sedimentary rocks of Ordovician? to Early Silurian age. The Hayachine Complex is, therefore, not an allochthonous block, but the basement of the "Tectonic Belt". The eastern boundary fault of the "Tectonic Belt" is a reverse one and steeply dips southwest. The geologic structure in the northeastern margin of the "Tectonic Belt" and in the Northern Kitakami Massif, as a whole, is characterized by overturned folds with axial planes dipping to the southwest. On the contrary, in the southwestern margin of the "Tectonic Belt" and in the northeastern margin of the Southern Kitakami Massif, high-angle reverse faults and asymmetric or overturned folds with southwest vergence are prevalent. The basement rocks, the Hayachine Complex, occur in the " Tectonic Belt", and thus the boundary zone between the Southern and Northern Kitakami Massifs seems to form a broad anticline, which associated with longitudinal reverse faults on both flanks. The Hayachine Complex is infered to have been formed in a rift zone, which originated on the continental margin, in Ordovician or Early Silurian time. During Middle Palaeozoic to Early (Middle?) Mesozoic, the "Tectonic Belt" was a site of passive margin. In the latest Jurassic, the Palaeozoic strata with the Hayachine Complex in the passive margin began to uplift, in connection with the accretion in the Northern Kitakami Massif, and leading to the formation of the said anticline. The "Hayachine Tectonic Belt" is the axial part of this anticline.
地学団体研究会の論文
1988-11-25

"早池峰構造帯"研究の現状と課題

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