Rift Evolution and Magmatic-Tectonic-Stratigraphic Records of Episodic Seafloor Spreading at Southwest Sub-Basin of South China Sea
Yang Tianyi
Tang Yong
Ren Jianye
Chao Peng
Abstract：The formation and evolution mechanism of the passive rift margin under the marginal sea background is still controversial,especially existing studies on the structural characteristics and formation process of the oceanic and continental transition zone are insufficient.In order to deeply explore the tectonic structure and evolution characteristics of the rift margin and oceanic transition zone of the South China Sea(SCS)under the background of marginal sea,this study presents an investigation of the seismic profiles across the V-shaped tip of the Southwest Sub-basin of the SCS,identifying three first order rift margin interfaces including the Moho,Top of basement,and seafloor.The tectonic units of the conjugate margin are subdivided into the necking domain,the hyper-extended domain,and the proto-oceanic domain.The study further refines the interpretation of the stratigraphic sequences and multi-phase fault systems at the conjugate margin as well as identifies the breakup unconformity surface Bi.We divide the syn-rift sequence(between Tg and Bi)into five sequence units(S1-S5),establishing a tectono-stratigraphic framework for the conjugate margin of the SW sub-basin of the SCS.The study indicates that the interface CBi between S3 and S4,as well as the interface POBi between S4 and S5,corresponds to the break-up of continental crust and proto-oceanic crust Ⅰ,respectively,recording important tectonic events during the rifting.Based on the analysis of fault activity and basin prototyping,we divide the evolution of the conjugate margin into four stages:stretching,necking,hyper-extending,and proto-oceanic crust developing,establishing the rift margin evolution model for the conjugate rift margin of the SW sub-basin of the SCS.This study also identifies a"crocodile-jaw"structure in the crust of the conjugate margin of the V-shaped tip at the SW sub-basin of the SCS,recognizing two phases of proto-oceanic crust with total width of 231 km.Based on the investigation of the outer high and syn-breakup sequence(S4 and S5),we propose that the two phases of proto-oceanic crust developing correspond to two episodes of the seafloor spreading at SW sub-basin of the SCS,and that the proto-oceanic crust constitutes the oceanic-continental transition zone between the continental margin and the synchronous oceanic crust.This study reveals the mechanism of the lithospheric thinning and break-up,and the influence of episodic seafloor spreading during the ridge propagation process on the tectonic structure,stratigraphic sequence and magmatic activity.The research will significant deepen our understanding of the rifting process at the SCS,causes of oceanic-continental transition zones,and dynamic mechanisms involved in the formation of passive continental margins at the SCS.
Keywords：South China SeaSouthwest Sub-basinrift margin evolution modelepisodic seafloor spreadingproto-oceanic crustoceanic-continental transitionmagmatic-tectono-stratigraphic recordsmarine geology
Publication Date：2025-01-14
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：22( 195-216 )