Rifting in Marginal Seas of the Wstern Pacific

Abstract

The paper presents a review of structural features of rifting during the formation of Cenozoic basins of marginal seas of the Western Pacific. The assumption that rifting always starts with a passive stage and is only occasionally interrupted by episodes of active rifting is fully confirmed by examples from the studied basins. Rifting occurred under a compressive regime with NE and NNE-directed shortening that resulted in the formation of either a chain of pull-apart basins or rifts scattered between major strike-slip faults in the great part of the South China Sea. The NE and NNE directions of horizontal compressive force are apparently related to the convective currents in the asthenospheric mantle that have extended from the spreading ridge of the Indian Ocean and have carried plate fragments deformed to some extent during their transportation. The north-northeastward drift of the Indian, Australian, and Eurasian plates associated with these mantle currents does not reveal any connection with subduction from adjacent Paleo-Pacific plates, which continue to move in the NW direction up to the present time. Thus, formation of the marginal basins of the Western Pacific were unaffected by subduction from the Pacific Ocean side and they can be regarded as back-arc basins only due to their geographical locations.