Collaborative Research: Spreading Ridge-Trench Interaction Recorded in an Accretionary Prism: The Tertiary Shimanto Belt, SW Japan

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Accretionary prisms are one of the major components of convergent plate orogens, forming the pliant leading edge of the overriding crustal plate. The Shimanto accretionary complex in southwest Japan has received recent study because portions are well-exposed so that detailed structural and stratigraphic relation-ships can be investigated. Results of that study have revealed t hat parts of this accretionary prism are a typical of simple accretion at convergent plate margins. The structural anomalies include a 180o reversal in structural polarity between Eocene and Miocene accreted packets and late stage oroclinal flexing. This renewal will test the hypothesis that these anomalies are attributable to a Miocene episode of spreading-ridge subduction, by a program of computer modeling and further analysis of existing data. Results are expected to clarify the significance of the Shimanto deformational data and explore the role of subduction of actively spreading ridges in accretionary complexes.