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

1. 分析了Hidaka变质带变质岩的顺时针P-T路径，确定了4个变形变质期；(1)高P/T条件下增生-弧前沉积变质的构造增厚；(2)辉长岩-闪长岩岩浆作用等压加热，形成岛弧变质地壳；(3)地壳层次水平位移形成双相构造，导致压力释放；(4)双相右向逆运动，等压冷却。利用Ca-A1矿物将Kamuikotan高压片岩划分为3个带；lawsonite-pumpellyite z二世。lawsonite-pumpellyite-epidote z,三世。P-T空间的Schreinemakers分析显示出相对陡峭的P/T梯度。在Tokoro带中首次发现了na -角闪洞、na -辉石、钠长石和文石，并将其划分为4个变质带。这一事实支持了白垩纪两次俯冲方向相反的俯冲的观点。

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.