Correlation of the Eocene subduction complex in Kyushu-Ryukyu Arc.

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Lateral change of tectono-sedimentary evolution of the Eocene subduction complexes of Kyuushu and Ryukyu Arc were examined from the analysis of sedimentary and deformation faceis. environments, and ages in terms of microfossils.The Hyuga group in Kyushu. late Middle Eocene to Early Oligoceneages, can be reconstructed as a typical subduction complex, that consists of a fully grown accretionary prism developed by both underplanting and offscraping processes, a trench slope deposits, and a forearc basin sequence. All of the units are of the contemporaneous hetrotopic facies. Development of the subduction complex may indicate a orthogonal sub-duction process. The wano Formation in Amami-Oshima and the Kayo Formation in Okinawa Island, late Middle Eocene age, represent deep-sea fan sequences accumulated in a slope- inner to middle fans, and in a large scale channel terrace, respectively. Both of the formations show a complicated fold structures, but exclude any accretionary deformations. They can be attributed to a consumption forearc, because of presence of the Creraceous basement beneath the forearc basins.The difference in framework of forearc between Kyushu and Ryu may suggest the regional variety of convergent angle of the subducting Philippine Sea Plate along the proto-Ryu arc of Eocene time.