Accretionary complex origin of the Sanbagawa, high P/T metamorphic rocks, Central Shikoku, Japan. Layer-parallel shortening structure and greenstone geochemistry.

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Despite suffering extensive penetrative deformation and high-grade metamorphism up to 600°C and 10-12 kb, Sanbagawa schists of SW Japan preserve imbricate structures and oceanic plate stratigraphy, of MORB, pelagic bedded chert, hemipelagic rocks and overlying turbidites. The field occurrence and petrochemistry of the metabasites suggest that a back-arc basin setting or a passive continental-margin setting is unlikely for their origin. Instead, we suggest that the protoliths of Sanbagawa schists formed in a part of an oceanic plate prior to Cretaceous subduction and incorporation into an accretionary complex.