Lithosphere Stretching Model of Deep Water in Qiongdongnan Basin,Northern Continental Margin of South China Sea,and Controlling of the Post-Rift Subsidence

In order to thoroughly explain the mechanism of significant subsidence in deep waters of Qiongdongnan basin,a rifted continental marginal basin,we analyzed the high resolution seismic reflection profiles in the study area,and conduct a quantitative study on upper-crust,whole crust and whole lithosphere stretching and thinning respectively by incorporating flexural cantilever model and flexural cantilever isostasy model and using both forward and reverse basin modeling techniques Our integrated analysis shows that the extension in brittle upper crust decreases from shelf to deep basin. And the largest amount of stretching factor β is 1.23-1.32; the whole crust stretching factors change from β=1.1-1.2 of uplifts in basin margin to β=3.14 in central basin; And estimates of the whole lithosphere stretching factor change from β=1.2 on continental shelf to β=4.2 in deep basin. Theanalysis of tectonic geology involving lithosphere and crust,depth-dependent stretching of lithosphere in Qiongdongnan basin described above is closely related with sea floor spreading of northwestern South China Sea,which caused the discrete upwelling flow of middle and deep substance,then it resulted in the plastic flow of the lower crust rapidly and intensely. This model is different from the depth-uniform lithosphere stretching model and its slow post-rift subsidence controlled by geothermal isostatic re-equilibration (McKenzie,1978). The formation and evolution model of Qiongdongnan basin is proposed to interpret the mechanism of rapid and large-amplitude post-rift subsidence in deep water.