The Eocene Kayo Formation exposed at the southwestern end of the Shimanto Belt in the Ryukyu Arc records the progressive development of off-scraping accretion accompanied by increase in lithification and burial as well as synaccretionary thermal imprint. The formation consists almost wholly of coherent trench turbidites supplied by axial currents. Detailed structural analysis has revealed that two successive deformation stages are recognized in the Formation. The early deformation (stage 1) occurred by horizontal shortening related to the initial stage of off-scraping accretion. In this stage, sands were water-rich and nearly unlithified, and the competence contrast between sandstone and shale was low. The late deformation (stage 2) is marked by the formation of seaward verging imbricate fold-and-thrust system within the accretionary wedge. Compared with stage 1, sands in stage 2 were more dewatered and lithified, and the competence contrast between sandstone and shale increased. In accordance with this deformation history, structures caused by high pore fluid pressure indicate increased cohesion of sands during off-scraping accretion. Studies of the vitrinite reflectance and the illite crystallinity clearly suggest that the Formation became buried and suffered thermal imprint; pressure solution cleavage developed as an axial planar to the stage 2 folds. Thermal imprint on the Formation is characterized by high paleotemperatures at approximately 250 ¿C--300 ¿C in a region of the prehnite-pumpellyite facies metamorphism. This thermal event took place during and slightly after the stage 2 probably associated with subduction of a young and hot oceanic plate.¿ 1997 American Geophysical Union