On the diabase at the Meguro district, Hidaka Province, Hokkaido

Abstract

There is a distinct difference in the distribution of the igneous rocks between the western and the eastern part of the Hidaka metamorphic zone. The peridotites and gabbroic rocks are widely distributed in the western part. The granites mainly occur in the eastern part. Meguro district is situated in the south-eastern part of the Hidaka Mountains. From petrological features, metamorphic zone of this district can be classified into the following six zones. 1. hornfels, 2. schistose hornfels, 3. banded gneiss, 4. cordierite migmatite, 5. gneissose migmatite, 6. granitic migmatite. These metamorphic rocks and migmatites are intruded by dikes of basic igneous rocks, such as diabase, dioritic gabbro, hornblende gabbro and amphibolite. It seems probable that the above-mentioned basic plutonic complexes and the basic dikes are geneticaly related. The diabases which occur as minor dikes (2-3m in average width) are more abundant than the other dike rocks. The diabase may furnish clues that will suggest further data necessary to solve a problem of the mutural relation between the migmatites and the basic igneous complexes. In the present paper, the writer have described the mode of occurrences and the microscopical features on the diabases. Some considerations on the distribution, alteration and intrusion of the diabases are given.