ACCRETIONARY PRISM FORMATION IN OBLIQUE SUBDUCTION ZONES: COMPARATIVE STUDY IN SPACE AND TIME

We have investigated through on-land and submarine studies the internal structure of accretionary prisms (AP) developed at oblique subduction zones, where downgoing plates contain continental masses. In the Indo-Myanmar region, AP sediments derived from the passive margin of the downgoing Indian plate and the Burma upper plate are deposited–deformed east of the Andaman Trench. West-directed thrust faults and folds predominate in the Myanmar AP. In the Miura-Boso Peninsula on Honshu Island (Japan) Neogene AP sediments are exposed on-land to the east of the Sagami Trough, where the Philippine Sea plate (PHS) is subducting beneath the North America plate. The Izu-Bonin island arc in the PHS has been colliding with the Honshu arc since middle Miocene (ca. 15 Ma), forming the Kushigata-Tanzawa collision zones. Sediments in the Sagami–Nankai APs are derived from both those collision zone, Honshu, and the Izu volcanic arc on the downgoing PHS. We mapped three on-land AP complexes (Miocene to Recent) on Honshu, the seafloor bathymetry and geology of the modern AP in the Sagami Trough by submersible studies, and the Cretaceous–Recent AP exposed in Myanmar. The Japanese APs constitute turbiditic sequences, displaying syn-sedimentary structures, caused by liquefaction, fluidization, folding-faulting, and submarine sliding. Various types of duplex structures in several stages, fault-bend folds and fault-propagate folds are also abundant. Rapid exhumation of these units are also significant. All these structures attest to dynamic deformation during AP development at oblique subduction zones. Seismic, tsunamogenic, volcanic and crustal movement during subduction-collisional events were also involved in devastating natural disasters.