Crystalline schists of Yokokawagawa district (Yokokawagawa metamorphic rocks), north of Lake Suwa, Central Japan

Abstract

The Yokokawagawa metamorphic rocks which have long been thought to be northeastern extension of the Sambagawa metamorphic rocks of northern end of Akaishi mountains are studied from the viewpoint of structure as well as metamorphism. They are divided into two zones. The one is so-called spotted schist zone where garnet is stable in pelitic rocks, and porphyloblastic albite is widely developed. The other is so-called non-spotted schist zone where garnet is unstable and no porphryoblastic albite is developed. The metamorphic grade increases toward west in relation to descending order of stratigraphy. Comparing these rocks with Sambagawa metamorphic rocks of northern Akaishi mountains, structural and metamorphic similarities are found. The lateral displacement of the rocks by the fault of the western margin of the Fossa-Magna is estimated as 12 Km in left lateral sense. The origin of schist pebble in the Neogene formations in the Fossa-Magna region must be sought partly in this area.