東北日本の深成変成岩類の相互関係

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The Japanese Islands are divided into the two parts by the Fossa-Magna area, Southwest Japan and Northeast Japan. In the Southwest Japan the zonal distribution of the metamorphic belts nearlyparallel to the shape of the Islands is well recognized ; that is, from north to south the Hida belt, probably pre-Cambrian and characterized by granite and gneiss, the Sangun belt, late Paleozoic and metamorphosed under the condition of glaucophane-schist metamorphism, the Ryoke belt, late Paleozoic-early Triassic and characterized by granite and gneiss, and the Sanbagawa belt, late Paleozoic and metamorphosed under the condition of glaucophane-schist metamorphism. It has long been an important problem what the prolongations of such belts in the Southwest Japan are in the Northeast Japan. However, such zoning of metamorphic belts is not recognized in the Northeast Japan. The writer divided the Paleozoics and the older rocks of the Northeast Japan into four belts ; that is, from west to east, (1) Jaetsu belt, (2) Ashio belt. (3) Abukuma belt and (4) Kitakami belt. 1. Joetsu belt is characterized by glaucophane-schist metamorphism and intrusions of ultrabasic rocks. The original rocks are probably Paleozoic, but the certain ages of the rocks and metamorphism are not distinct. The distribution of these rocks is very narrow, because the wide area of the belt is covered by the young sediments and volcanics. 2. Ashio belt is composed of Upper Paleozoic formation and is free from any regional metamorphism. 3. The Abukuma belt is the plutonic and metamorphic belt, in which two stages of metamorphism and plutonism are discriminated. The earlier one is the pre-Gosaisho-Takanuki metamorphism and the later one is the Older Abukuma plutonism and metamorphism. The former may be the Dalradian type metamorphism, characterized by staurolite-and kyanite-bearing schists, almandine-amphibolites, cordierite free biotite gneisses etc., and the age of the metamorphism may be pre-Cambrian. The latter is a regional consact metamorphism, characterized by common biotite-schists and biotitegneisses with great quantities of granitic rocks, and the age of the plutonism and metamorphism is late-Paleozoic-early Mesozoic. The metamorphic character of the preGosaisho-Takanuki metamorphic rocks is changed by the Older Abukuma plotonism and metamorphism, of which original rocks are preGosaisho-Takanuki metamorphic rocks and the Upper Paleozoic formations. 4. The Kitakami belt is composed of the Upper Paleozoics, in which two divisions are distinguished by the metamorphism ; that is, the Matsugadaira-Motai metamorphic rocks and non-metamorphic rocks. The Matsugadaira-Motai metamorphic rocks are formed under the condition of glaucophane-schist metamorphism, being composed of various schists derived mainly from the Lower-Middle Devonian. The non-metamorphic rocks are younger than Upper Devonian. In the Northeast Japan as wellasin the Southwest Japan great quantities of granitic rocks are intruded in Cretaceous. The divisions mentioned above are controled by this Cretaceous movement and the older rocks mentioned above are also modified by this granitic intrusions.
地学団体研究会の論文
1963-07-25

東北日本の深成変成岩類の相互関係

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