The “Homeland” of the Torinosu-Type Limestone in Relation to Jurassic Accretionary Tectonics in SW Japan
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Upper Jurassic–Lower Cretaceous fore-arc basin deposits cover the oceanic plate sequences (OPSs) of the Permian and Jurassic accretionary complexes (ACs) in the Outer Zone of SW Japan, facing the Pacific. In this study, special attention is given to the Torinosu-type reef limestone blocks in the fore-arc basin deposits, in search for a continental shelf facies from which to derive them, in relation to the subduction–accretion tectonic evolution of the Asian margin in the Japan segment. Finding such a margin facies may resolve questions about the palaeogeographical relationships and identity of the Kurosegawa Permian accretionary terranes and South Chichibu Jurassic accretionary terranes. The in situ Torinosu-type reef limestones in the Toyonishi Group (Akiyoshi Terrane in the Inner Zone) as well as those in the Birafu Formation of the Sakashu Group (Kurosegawa Terrane, Outer Zone) of SW Japan, suggest a “homeland” for the Torinosu-type limestone blocks, which were transported as olistoliths by submarine mass-wasting events from the continental shelf thrust nappe into the fore-arc basins during subduction–accretion.
KeywordsJurassic Oceanic plate stratigraphy Accretion terrane Fore-arc basin Torinosu-type limestone SW Japan
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