Granulite facies metamorphism and anatexis in the Hidaka metamorphic belt, Hokkaido, northern Japan

1)对Hidaka变质带麻粒岩片麻岩的P-T分析表明，峰值（dl阶段）时，800 ~ 850个C， 7 ~ 7.2kb，水平位移形成复式构造（D2）时，700 ~ 750个C， 5kb，最终隆升运动伴随平移和挤压引起的右向横向滑动时，600 ~ 400个C， 3kb。2)在变质峰期，花岗质至调性岩浆被认为是由泥质和砂质片麻岩深熔形成的。化学和矿物学分析表明，Opx-Gt-Cd麻粒岩是Gt-Cd片麻岩部分熔融形成花岗质熔体后留下的残石，呈脉状或荚状。在更深的部分，可能发生了更大程度的部分熔融，在Hidaka带形成了大型的调性岩体。3)对调性岩浆成因和结晶过程的岩石学和实验研究表明，该岩浆形成温度可能高于950ºC，深度大于8kb，熔融岩石中含有4-5%的水，当温度从900ºC降至700ºC时，结晶发生在5-6kb。矿物结晶产物为Gt-Pl-Opx-Bt-Qz-Cd-Kfs。Opx的稳定性很大程度上受岩浆中Or含量的控制。4)研究了中新世石曼托花岗岩的变质包裹体，比较了Hidaka带的变质和变形过程。在花岗岩形成之前，石曼托增生三棱镜发生了高温-低压区域变质作用。增生棱柱的区域热力过程在日本高温地体如日高和良差变质带中相当普遍。(5)黎奥克带的片麻岩品位最高，在14km深度达到700cc。在深部，花岗质岩浆可能是由片麻岩的深熔作用形成的。杂岩和片麻岩的稀土元素分析证实了这种可能性。6)在自然环境中，实际的熔融过程只在高温岩浆中的岩石包体中观察到，如滑石岩和玄武岩。他们的研究表明，岩石的融化非常不均匀，由于高粘度，熔体很难相互混合。少

1) P-T analysis of granulite pacies gneisses in the Hidaka metamorphic belt show 800-850ﾟC, 7-7.2kb at the peak condition (Dl-stage), 700-750ﾟC, 5kb during horizontal displacement forming duplex structure (D2) and 600-400ﾟC, 3kb during the final uplifting movement accompanying tilting with dextral transcurrent slip due to transpression.2)During the peak metamorphic condition, granitic to tonalitic magmas are thought to have form through anatexis of pelitic and psammitic gneisses. Chemical and mineralogical analysis indicate that Opx-Gt-Cd granulites are restites left after partial melting of Gt-Cd gneisses to form granitic melts which occur as veins or pods. In deeper part, larger extents of partial melting might have occurred to give rise large tonalitic plutons in the Hidaka belt.3)Petrological and experimental studies on the genesis and crystallization of tonalitic magma indicate that the magma might have formed at higher temperature than 950ﾟC and deeper than 8kb, with 4-5% water c … More ontained in the melted rocks, and that the crystallization took place at 5-6kb when the temperature decreased from 900 to 700ﾟC. The crystallising orger of minerals is Gt-Pl-Opx-Bt-Qz-Cd-Kfs. The stability of Opx is largely controlled with Or contents of the magma.4)Metamorphic enclaves in Miocene Shimanto granites were studied to compare the metamorphic and deformational processes in the Hidaka belt. The high temperature-low pressure regional metamorphism took place in the Shimanto accretionary prism prior to generation of the granites. The regional thermo-dynamic process in accretionary prisms is rather common in the Japanese high temperature terranes such as Hidaka mentioned above and Ryoke metamorphic belt.5)The highest grade gneisses in the Ryoke belt attained at 700ﾟC at 14km deep. In deeper part, granitic magmas are expected to have been formed through anatexis of gneisses. REE analysis of migmatite and gneisses confirmed the possibility.6)Actual melting processes in natural environments are only observed for rock enclaves within high temperature magmas such as tonalite and basalt. Their examinations argue that rocks melt very heterogeneously, and that the melts are hardly mixed each other owing to high viscosity, . Less