Geological Structure and Dynamics of the Yinggehai Active Rift Basin,South China Sea

The Yinggehai Basin is a unique NNW-trending petroliferous basin in the northwestern South China Sea.This paper mainly utilized stratigraphic,tectonic and seismic data by characterizing the geological structures and conducting the geo-mechanical analysis to study the formation,evolution and dynamics of the Yinggehai Basin.The study indicates that the Ailaoshan-Truong Son extruded terrane is composed of multiple secondary extruded bodies.The Red River fault zone,located within the Qiangtang-Simao-Yinggehai mantle flow channel and basin zone,experienced transform-type sinistral strike-slip motion before the basin forming stage and formed a NW-trending extruded mantle uplift,which activated the Yinggehai basin.After experiencing the rift depression,fault depression,and fault subsidence,the basin eventually formed large-scale,thick sedimentation features with ideal hydrocarbon-forming conditions at the end of the Miocene.Later,the basin dynamically transformed and entered a period of tectonic superposition,reworking,and thermal subsidence.Superposition of the NNW thrust sinistral strike-slip fault zone on the northern Hanoi sub-basin complicated the basin structure.Since the Pliocene,the southern Yinggehai main basin has been transformed into an extensional dextral strike-slip environment that hosted numerous mud diapirs.The thin crust and high geothermal gradient provide favorable conditions for the large-scale accumulation of natural gas.

Major Tectono-thermal Events in the Yangtze Craton: Insights from U-Pb-Lu-Hf Isotope Records in Zircons from End-Permian Volcanic Interlayers in Southwest China

The in situ zircon U-Pb-Lu-Hf isotope records from end-Permian volcanic interlayers in southwest China,integrated with previous studies,restructure the evolutionary history of the Yangtze Craton from Precambrian to Late Paleozoic.This includes early continental crust formation before 3.0 Ga and massive juvenile crustal growth at 2.6-2.4 Ga;large-scale crustal reworking at 2.1-1.7 Ga;Neoproterozoic crust addition at 1.1 to 0.7 Ga;collision and subduction along the craton margin between 700-541 Ma;Early Ordovician to Late Silurian magmatism;and large tectono-thermal events in the Middle Carboniferous to end-Permian.Some zircons with T(MD2)ages from 4.40 to 4.01 Ga and lower initial176Hf/177Hf values of 0.280592 to 0.280726 may imply the existence of Hadean crust relics beneath the Yangtze Craton and their provenances could be associated with Hadean crustal remelting.This study further clarifies that the Precambrian-age zircons between the end-Permian volcanic interlayers,the complexes in the western margin of the Yangtze Craton,and the sedimentary Kangdian Basin,may share an affinity based on similar U-Pb age spectra and Hf isotope features.It also shows that the Neoproterozoic tectono-thermal event may be associated with large-scale tectono-rifting activity,which is different from the Grenville-age continental collision between Yangtze and Cathaysia blocks in South China.The above findings support the inference of a widespread Archean basement extending to the western Yangtze Craton and a provenance in the Kangdian Basin that is derived from the weathering and erosion of Paleoproterozoic continental crust.