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

1)日高变质带中麻粒岩类的P-T分析表明，峰期温度为800-850 ℃，峰值温度为7-7.2kb（D_1期）700-750 ℃，水平位移5 kb，形成复式构造（D_2期）;（D_2期）600-400 ℃，最后隆升3 kb，伴随着倾斜和压扭作用的右旋走滑。花岗质到英云闪长质岩浆被认为是通过泥质和砂质片麻岩的深熔作用形成的。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残留的残橄岩，呈脉状或豆荚状产出。3）对英云闪长质岩浆的成因和结晶作用的岩石学和实验研究表明，该岩浆形成的温度可能高于950 ℃，形成的深度可能大于8 kb，含水量为4-5%。 ...更多信息 当温度从900 ℃降至700 ℃时，结晶发生在5- 6 kb处。矿物的结晶组织为Gt-Pl-Opx-Bt-Qz-Cd-Kfs。Opx的稳定性在很大程度上受岩浆中Or含量的控制。4）研究了中新世四万十花岗岩中的变质包体，以对比日高带的变质和变形过程。在花岗岩生成之前，四万户增生棱镜中发生了高温低压区域变质作用。增生棱柱体中的区域热动力过程在日高等日本高温岩体和辽辽变质带中相当普遍。5）辽辽变质带中的最高级片麻岩在700 ℃时达到14 km深。在深部，花岗质岩浆可能是通过片麻岩的深熔作用形成的。混合岩和片麻岩的稀土元素分析证实了这种可能性。6）只有英云闪长岩和玄武岩等高温岩浆中的岩石包体才能观察到自然环境中的实际熔融过程。他们的研究表明，岩石的熔化是非常不均匀的，而且由于粘度高，熔化物很难相互混合。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