Petrology and tectonics of Hidaka, Kamuikotan and Tokoto belts in Hokkaido, Japan

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1. A clockwise P-T path of metamorphic rocks was analyses for the Hidaka metamorphic belt, in which 4 deformational-metamorphic stages were defined;(1)tectonic thickning of accretional-forearc sediments metamorphosed under high P/T regime, (2) isobaric heating due to gabbro-diorite magmatism, giving rise to formation of an island arc metamorphic crust, (3)subhorizontal displacement of the crustal layer to form duplex structure, resulting in pressure release, and (4)dextral-reverse movement of the duplex with isobaric cooling.2. The Kamuikotan high pressure schists were divided into 3 zones using Ca-A1 minerals;I. lawsonite-pumpellyite z.,II. lawsonite-pumpellyite-epidote z.,III. oumpellyite-epidote z. The Schreinemakers analysis of the parageneses show relatively steep P/T gradient in P-T space.3. Na-amphibole, Na-pyroxene, lawsonite and aragonite were first found in the Tokoro belt, by which the belt was divided into 4 metamorphic zones. The fact supports a thought of two Cretaceous subductions with opposite subduction directions.