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

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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.