九頭竜川上流地域における飛だ外縁帯の低度変成岩類

Abstract

Low-grade metamorphic rocks occur in small areas of Ise and Hakogase, Izumi-mura, Fukui Prefecture. Geologically, they lie in the Hida marginal belt. The rocks are divided into two major units based on their geographical distribution: the Ise and Hakogase masses. The Ise mass consists of metagabbro and basic schist with subordinate pelitic schist. Actinolite, epidote and chlorite are common metamorphic minerals in basic metamorphic rocks throughout the major part of the mass. Only in the limited southern part of the mass, hornblende and biotite are found in basic and pelitic schists, respectively. Garnet is also found in the southern part of the mass. The Hakogase mass consists of basic and pelitic schists. Characteristic metamorphic minerals are soda amphibole, epidote, chlorite, actinolite, lawsonite and pumpellyite in basic schists and muscovite, chlorite and stilpnomelane in pelitic schists. Mineral associations indicate that the Ise mass belongs to the greenschist facies up to the albite-epidote amphibolite facies probably with an increase in metamorphic grade southwards and the Hakogase mass belongs to the glaucophane schist facies throughout the mass. Both the masses differ from each other in metamorphic grade but are products of the same glaucophanitic metamorphism.