Structure and petrofabrics of the Ryoke metamorphic rocks in the Takato district, Nagano Prefecture

Abstract

The Ryoke metamorphic rocks of the Takato district are composed mainly of pelitic and psammitic rocks, with subordinate amounts of basic volcanic rocks and limestone. The grade of metamorphism of the district increases progressively from the northwest to the southeast. Petrofabric analysis has been carried out for biotite, muscovite and quartz in the pelitic schistose hornfelses and gneisses of the district. Biotite and muscovite fabrics are generally determined by the bedding schistosity, and quartz fabrics of the schistose hornfelses show weak symmetry and ac-girdle, while those of the gneisses do not show any symmetrical pattern. When compared with those of the Yanai district belonging to the Ryoke metamorphic belt in southwestern Japan, the fabric diagram mentioned above are less symmetrical. This fact may suggest that the movement during the Ryoke metamorphism was different between the Takato and the Yanai districts.