Post-Rift Faulting And Magmatism Within The Pearl River Mouth Basin:Spatial-Temporal Difference,and New Insights Into The Geodynamics

The South China Sea is located at the junction of the Eurasian Plate,the Pacific Plate and the India-Australia Plate,developed as the result of Cenozoic rifting and the diachronous continental breakup during the Early Oligocene.The Pearl River Mouth Basin is located in the mid-segment of the northern continental margin of the South China Sea.By studying the geological evolution of passive continental margin basins worldwide,it is suggested that almost all passive continental margin basins have experienced different kinds of tectonism and magmatism influenced by complex mechanisms,which are mainly related to the geological environment of the basin itself and the interaction between the surrounding plates.The Pearl River Mouth Basin also experienced different tectonism and magmatism during the post-rift stage,including faulting,magmatism,subsidence and uplift.However,there are still some key scientific problems unresolved due to the limitations of data and research area,especially the spatial and temporal differencesof faulting and magmatism,as well as the dynamic mechanisms.Based on the latest 2d and 3D seismic data covering nearly entire the basin,drilling data and basalt samples,the faulting and magmatism during the post-rift stage of the Pearl River Mouth Basin are comprehensively studied,including the temporal and spatial differences,as well as the dynamics combined with the regional tectonic setting,tectonic events developed within the basin and the geochemical research of the basalts collected from the Pearl River Mouth Basin.Faulting during the Zhuhai-Early Hanjiang stage showed migration from south to north and the fault activities showed weak-intensive-weak characteristics.Faulting since the Late Hanjiangstage showed migration from east to west and the fault activities also showed weak-intensive-weak characteristics.During the Zhuhai Stage,the Pearl River Mouth Basin underwent extension under the influence of the mantle flow caused by the collision between the Indian plate and the Eurasian plate,and the fault activities weremost intensive within the Zhu IV Depression.During the Early Zhujiang Stage,increased fault activities caused by the anomalous subsidence occurred within the Baiyun Sag influenced by the decreased mantle flow.And the fault activities occurred within the Baiyun Sag were the most intensive within the Pear River Mouth Basin during this stage.During the Late Zhujiang Stage,large amounts of sedimentswere transported to the Baiyun Sagunder the influence of enhanced East Asian Summer Monsoon,which led to the lower crust flow from the Baiyun Sag to the continental margin of South China,and this process also caused anomalous subsidence and faulting within the Baiyun Sag and the Zhu I Depression.During this stage,the fault activities entire the basin reached peak since the Zhuhai Stage.during the Early Hanjiang Stage,the faulting and anomalous subsidence within these areas all decreased due to the decreased lower crust flow.During the Late Hanjiang Stage,the arc-continent collision between Luzon Arc and Eurasia Continent began to affect the Pearl River Mouth basin,resulting in the activation of faulting within the Hanjiang Sag,which is located in the easternmost part of Zhu I Depression.During the Yuehai Stage,the arc-continent collision was further strengthened,and the fault activity center within the Pearl River Mouth Basin moved from east to west to the western Zhu I Depression,Panyu Lower Uplift,western Dongsha Uplift and the northern Baiyun Sag.During this stage,the fault activities entire the basin also reached peaksince the late Hanjiang Stage.During wanshan Stage,fault activities entire the basin decreased again due to the decreased arc-continent collision process.During the Zhuhai Stage-Early Hanjiang Stage,large numbers of approximately E-W striking faults developed within the Pear River Mouth Basin under the N-S stress field influenced by the approximately N-S mantle flow and lower crust flow.Since the Late Hanjiang Stage,large numbers of high dip angle faults with echelon,horsetail and conjugate "X" type of combination on plan view,as well as withflower-like structure and "Y" type of combination on the profile developed within the Pear River Mouth Basin under the influence of the collision between the Luzon Arc and the Eurasian ContinentFour stages of magmatism developed within the Pear River Mouth Basin during the post-rift stage under the combined influence of mantle flow generated by collision between India Plate and Eurasia Plate,the combined effect of activation of the deep-seated faults with Hainan Plume and the arc-continent collision.During the Zhuhai Stage,magmatic activities occurred within the Zhu IV Depression,dominated by magmatic intrusion,under the influence of mantles flow caused by the India-Eurasian Plate collision.During the Early Zhujiang Stage,magmatic activities occurred within the Yunkai Lower Uplift,Baiyun Sag and the Yunli Uplift,dominated by volcanic eruptions,under the influence of Hainan Plume and the reactivation of the southern segment of the deep-seated Yanjiang-Yitongansha fault zone.During the Late Zhujiang Stage-Early Hanjiang Stage,magmatic activities occurred within the eastern Zhu III Depression and the Enping Sag,dominated by volcanic eruptions,under the influence of Hainan Plume and the reactivation of the northern segment of the deep-seated Yanjiang-Yitongansha fault zone.Since the Late Hanjiang Stage,magmatic activities occurred within the southern Dongsha Uplift,dominated by volcanic eruptions and magma intrusions,under the influence of Hainan Plume and the reactivation of the deep-seated Dongshadong fault zone caused by the Luzon Arc-Eurasian Continent collision.The combined study of faulting and magmatismreveals that the Pearl River Mouth Basin experienced complexes geological processes during the post-rift stages as the follows: 1)the temporal and spatial co-development of faulting and magmatism during the Zhuhai Stage under the influence of mantle flow;2)the differential evolution of faulting and magmatism during the Zhujiang Stage-Early Hanjiang Stage under the multiple and different dynamic backgrounds,such as the lower crust flow,the mantle plume,and the reactivation ofyangjiang-Yitongansha fault zone.3)the relative co-development of faulting and magmatismsince the Hanjiang Stage under the influence of mantle plume,and the reactivation of Dongshadong fault zone caused by the arc-continent collision.A multi-stage,multi-source and multi-dynamic magmatic evolution model of the Pearl River Mouth basin during the post-rift stage is proposed,which is different from the magmatic evolution model with single dynamic mechanism,and provides a new case for the study of the post-rift magmatism within the passive continental margins.This study also established the post-rift faulting-magmatism evolutional model with dynamics within the Pearl River Mouth Basin,and provides a new case for the joint study of faulting and magmatism worldwide,which is of great significance to promote the post-rift study of the passive margins.