IZANAGI sidescan sonar and high-resolution multichannel seismic reflection line interpretation of Nankai accretionary prism and trench, offshore Japan

Abstract

The Nankai Trough region (Fig. 7.1) is one of the most studied Cenozoic active convergent plate margins. To the south of the Nankai Trough the Shikoku Basin is an elongated marginal basin forming the north-eastern part of the Philippine Sea Plate. From late Oligocene to middle Miocene times seafloor spreading occurred behind the Izu-Bonin arc-trench system to progressively separate the Kyushu-Palau Ridge from the active Izu-Bonin intra-oceanic island arc. Magnetic anomaly data suggest that between 14 and 12 Ma there was a late phase of east-west spreading limited to the axial northernmost Shikoku Basin, also associated with a counter-clockwise rotation of the spreading direction. The stratigraphy of the various Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites in the northern Shikoku Basin and Nankai Trough accretionary prism are summarized by Pickering et al. (1993a) and the general geology by Taira and Pickering (199D and Pickering and Taira (1994).