SUBDUCTION AND ACCRETIONARY HISTORY OF JAPAN AND THE WESTERN PACIFIC

Phanerozoic accretionary complexes are widely distributed in Japan and the Western Pacific region. Based on the time and space distribution of these accretionary complexes, the geological history of Japan and the western Pacific is divided into five stages. Stage 1 encompasses the Cambrian to Devonian periods, and is characterized by the development of ophiolites, high-pressure metamorphic rocks, and forearc sedimentary sequences. Stage 2 is represented by the formation of a Late Devonian to Carboniferous accretionary complex. Stage 3 witnessed the formation of Permian accretionary complexes and Permian – Early Triassic high-pressure metamorphic rocks. Accretionary complexes of Stages 4 and 5 extend from the Russian Far East in the north to the Indonesian archipelago in the south through the Japanese Islands. Stage 4 ran from the early Jurassic to the earliest Cretaceous, whereas Stage 5 spanned from the late Early Cretaceous to the Paleogene. In stage 6 (Neogene–Present), a major accretionary complex has developed along the Nankai Trough, but tectonic erosion has been a dominant process along the other convergent margin of Japan. In stage 1, subduction–accretion complexes were formed along a vast island arc system offshore Gondwana. This island arc system migrated away from Gondwana together with the North and South China blocks and Indochina during the Devonian, just before the onset of Stage 2. An island arc system was situated at the eastern edge of Paleo-Tethys, adjacent to the active margin of the Asian continental mass in Stage 3. The North and South China blocks and Indochina collided to form a single continent prior to the beginning of Stage 4. Subduction initiation along the eastern margin of this newly developed continent led into a long-term active margin tectonics and the formation of an extensive accretionary complex in Japan and the western Pacific during Stages 4 and 5. Opening of the Sea of Japan as a marginal basin and other backarc basins along the western Pacific occurred throughout the Cenozoic in Stage 6.