ひだ変成帯東北部の深成岩と変成岩

第1報 岩石の分布と性質

抄録

Though a lot of geological and petrological studies on the Hida metamorphic region have been done and published since a decade or earlier by many researchers belonging to the Hida group, the north-eastern part of the Hida metamorphic region have not yet been studied from the standpoint of regional geology except the excellent work of the geological map sheet "Shiroumadake" in scale 1/75000 by Isou (1937). The writer wishes to state in the present paper the general feature of geology of the area in question and discuss the lithological characters of the plutonic and metamorphic rocks occurring there. The said area is famous for the occurrence of staurolite-cyanite schist rare in Japan. The main part of the present metamorphic zone is consists of metamorphics and plutonics belonging to two groups having the general structure of N-S trend, the so-called " Unazuki direction." One of them is the Hida metamorphic group in strict sense, composed of the paragneiss, orthogneiss and migmatite. The paragneiss is finer in the north and coarser to the south in grain size, therefore, the northeastern area is characterized by crystalline schist, while the southwest by migmatite. The orthogneiss is dioritic in composition and injects into the paragneiss conformably. A great number of crystalline limestone layers are embeded in them. Another of the two is the Funatsu type plutonics and metamorphics formed by the mylonitization and the potassium-metasomatism relating to the intrusion of Funatsu granodiorite. The writer recognized that at least, a part of the original rock of Funatsu-type metamorphics was a member of the Hida metamorphics, which suffered afterwards from the post magmatic potassium metasomatism following the intrusion of Funatsu granodiorite. He considered also that Funatsu plutonism might have taken place in the later Palaeozoic to earlier Mesozoic age, while Hida metamorphism occurred in earlier age than the former. But the writer can not yet conclude from his own observations whether the above two events are due to the different or the same orogeny.