Tectonics of the Outer Zone of Southwest Japan as inferred from microtextur of its constituen rock

日本西南部的外围地区由四个大型机组组成。秩父超级机组2号，三巴川超级机组。由高到低依次为赤池部一号机组和石门特大机组。根据三巴川巨型单元岩，特别是Saruta推覆（I+II）片岩和Fuyunose推覆片岩的显微结构，明确了在俯冲水道沉积中，伴随有构造侵蚀和上盘岩石的混合作用。通过对索高内推覆片岩的显微结构和P-T-t-D路径的分析，指出索高内推覆片岩由3个亚推覆体组成，即ST亚推覆体、KAT亚推覆体和NOM亚推覆体，按构造水平递减顺序依次下覆，压力和温度下降，下覆过程归因于俯冲物从俯冲通道控制点向上流动。从Sogauchi推覆片岩与Sakamoto-Niyodo推覆片岩（Chichibu megaunit I）的显微结构关系和P-T-t-D路径分析，认为Sambagawa巨型片岩是沿白垩纪辐合带的力学边界发掘出的高压变质岩。在变形的最后阶段，三巴川巨型片岩的褶皱表现为由弯曲流动型向弯曲滑动型的过渡。

The Outer Zone of Southwest Japan consists of the four megaunits.Chichibu megaunit II,Sambagawa megaunit.Chicibu megaunit I and Shimant megaunit in descending order of structural level.On the basis of microtextures of the Sambagawa megaunit rocks, especially Saruta nappe (I+II) schists and Fuyunose nappe schists, it has been clarified that in subduction channel sediment subduction occurs a accompanying tectonic crosion and mixing of the hanging wall rocks.From analysis of microtextures and P-T-t-D path of the Sogauchi nappe schists, it has been pointed out that they consist of three subnappes, ST subnappe, KAT subnappe and NOM subnappe in descending oreder of structural level, which are succesively underplated with downward decrease of pressure and temperature, and that the underplating processes is ascribed to upflow of subducted sehiments from control point of subduction channel.From relationship in microtextures and P-T-t-D path between the Sogauchi nappe schists and the Sakamoto-Niyodo nappe schists (Chichibu megaunit I), it has benn concluded that the Sambagawa megaunit schists as metamorphic rocks of high-pressure type were exhumed along the mechanial boundary of the Cretaceous convergence zone.The folding of the Sambagawa megaunit schists during the last phase of deformation shows a transition from flexural-flow type to flexural-slip type.