Gneisses at the Saruru river district in the southern Hidaka metamorphic zone, Hokkaidô.

Abstract

The gneisses of this district are classified, according to the structural views, into three main types as follows: 1. banded gneiss, 2. gneissose migmatite, and 3. schistose rock. The general trend of the rocks is NW-SE and the dip is 40°_??_60° NE. The banded gneiss occurs as a narrow belt along the marginal zone of the cordierite migmatite mass, while the gneissose migmatite and the schistose rock occur in the migmatite area. The banded gneiss and the gneissose migmatite are composed mainly of medium- to coarse-grained metamorphics such as biotite gneiss, garnet sillimanite-bearing cordierite muscovite biotite gneiss, kalifelspar biotite gneiss, tourmaline-bearing muscovite biotite gneiss, and sillimanite muscovite biotite gneiss, etc. The schistose rock is dark brown, and shows schistose or hornfelsic texture. It is composed of finegrained quartz, plagioclase, and biotite, containing muscovite, kalifelspar, and rarely garnet and tourmaline. In this paper, the results of volumetric relation of chief mineral constituents and plagioclase twin method are described and mutural relationships of the rocks are discussed.