The early stage of the development of the Sambagawa metamorphic belt estimated from the metamorphic clasts within the Kuma Group

对三钵川变质带的关东山脉、纪伊半岛和四国以及三郡变质带的若狭变质岩进行了地质调查和取样。我们从岩石学上比较了高级变质碎屑岩与目前在日本西南部出露的高P型变质岩以及其他变质岩，如来自希达、喜马拉雅和吉尔吉斯坦变质带的变质岩。利用电子探针对石榴石、角闪石、绿帘石和白色云母等矿物进行了化学分析，并对这些矿物进行了化学分带、背散射电子像和元素颜色图的研究。研究表明，熊群高级变质碎屑岩与伊劳、东鸣角闪岩群等构造块体中的绿帘角闪岩相变质岩非常相似，40 Ar/39 Ar测年结果表明，熊群高级变质碎屑岩的峰变质年龄为145-189 Ma，明显大于百志推覆杂岩的峰变质年龄（90-100 Ma）。熊麻变质碎屑的裂变径迹年龄（65-70 Ma）也比别志推覆杂岩的裂变径迹年龄（45-58 Ma）大。这些研究表明，熊马推覆杂岩是比别子推覆杂岩更早阶段的变质岩，它比别子推覆杂岩中的变质岩早被剥露。

Geological survery and sampling of the metamorphic rocks from the Kanto Mountains, Kii Peninsula and Shikoku in the Sambagawa metamorphic belt and Wakasa in the Sangun metamorphic belt have been done. We petrographically compared the high-grade metamorphic clasts with the high-P type metamorphic rocks presently exposed in southwest Japan together with the other metamorphic rocks such as those from the Hida, Himalayan and Kyrghstan metamorphic belts. We chemically analyzed the constituent minerals including garnet, amphibole, epidote and white micas by using an electron probe micro-analyzer, and also examined these minerals in respect to the chemical zoning, backscattered electron image and elemental color mapping. These studies revealed that the high-grade metamorphic clasts from the Kuma Group are very much similar to the epidote amphibolite facies metamorphic rocks within the tectonic blocks such as the Iratsu and Tonaru amphibolite masses.The 40Ar/39Ar dating results suggest that the peak metamorphic age of the Kuma metamorphic clasts is 145-189 Ma and obviously older than that of the Besshi nappe complex (90-100 Ma). The fission track age of the Kuma metamorphic clasts (65-70 Ma) is also older than that of the Besshi nappe complex (45-58 Ma). These studies suggest that the Kuma nappe complex is earlier stage metamorphic rocks compared with the Besshi nappe complex and it was exhumed earlier than the metamorphic rocks within the Besshi nappe complex.