Residual Subsidence Of The Cenozoic Rift Basin In The East Asian Continental Margin And Its Genesis Analysis

Mantle convection have a significant effect on basin evolution;however,research quantification of this relationship is difficult.To understand the formation mechanism and evolution of the Cenozoic rifting basins in the continental margin of East Asia,based on the Mckenzie rift basin model,we combined with basin extension data,backstripping technique and one-dimensional strain rate inversion method for 162 wells from 15 basins of the East Asian continental margin to calculated the residual subsidence during the syn-rift and post-rift stages.The spatial configuration of residual subsidence suggest a increase trend toward the subduction zone from 100-300 m in terrestrial areas to 1.2-1.8 km on the continental shelf.The residual subsidence in the South China Sea increases from the periphery of the South China Sea to the central ocean basin.The northern margin of the South China Sea has increased from 500-700 m in the nearshore area to 1.2-1.6 km in the pelagic area,while the southern margin increased from 0-200 m off shore to 1.6 km in the pelagic area.The comparison of the residual subsidence distribution with the deep tomography data shows that the residual subsidence distribution is coupled with the position and morphology of the stagnant slab within the mantle transition zone.As for the spatial-temporal evolution of residual subsidence,we find a northwestward extension trend of the main residual subsidence center in eastern China since 20 Ma and the north-north-westward migration of the subsidence center after 5Ma are consistent with the change of the subduction direction of the Pacific-Philippine Sea plate during the same period.In South China Sea,the extended migration process of the residual subsidence center in the Cenozoic is also consistent with the speculative Izanagi plate and the proto-South China Sea plate movement direction.Therefore,we suggest that the residual subsidence might be associated with the plate subduction history.The residual subsidence we have extracted can match the dynamic topography predicted by different methods in distribution mode and magnitude.Considering that our results are a regional model,it's also a refinement and complement to the global residual topography,and can provide important constraints for geodynamic models.In addition to the influence of mantle convection,there remains local anomalies in the distribution and evolution of residual subsidence in the study area.We speculate that those local anomalies might be induced by other factors such as plate detachment,regional tectonic activity and shallow lithospheric structure.