The Response Of Late Cretaceous-eocene Epoch Volcanic And Sedimentary Sequence In Sanshui Basin To The Tectonic Evolution Of The Northern Margin Of South China Sea

It is a challenging scientific question whether the volcanic-sedimentary records of the South China Sea region are associated with the cracking of the South China Sea.The Guangdong Sanshui Basin is the most complete area for the formation and preservation of the late Mesozoic early Cenozoic volcano sedimentary records near the northern margin of the South China Sea.Based on the systematic study of sedimentary sequence and the data of volcanic rocks of the Sanshui Basin,this paper studies the geological evolution of the basin from the early Cretaceous to the middle Eocene,and partly answers the important scientific question of how the volcano sedimentary records of the study area are responding to the continental margin properties and the early rupture of the continental continent.Through the analysis of volcanic and sedimentary assemblage,the evolution pattern of the basin in the late Mesozoic and early Cenozoic is clearly understood,and the evolution of alluvial fan,fan delta,deep lacustrine,delta,alluvial plain in the basin is summed up in the time dimension by combining the mudstone color index to analyze the change law of the basin water depth.On the basis of sequence identification and cyclicity analysis,combined with tectonic stress field and tectonic mode formed in the basin,four sequence patterns are divided: named extruded sequence,rift tensional sequence,balanced settlement sequence and backfill water sequence.In fact,corresponding to the nature of different continental margins,the Sanshui Basin shows a distinct two-stage evolutionary pattern as a Sedimentary Basin from Late Mesozoic to Early Cenozoic Evolving.The first stage is characterized by the basic characteristics of a forerunner-type intermountain basin with many depositional centers.It is generally developed in small,isolated piedmont depressions and the material sources of the filling basins are diverse.The second phase has the characteristics of an extended rift basin.The sedimentation center gradually converges and expands.It integrates within the basin and the source of material tends to be single.The two-phase division is generally located between the Dalangshan Group and the Xinzhuangcun Group at the turn of the Mesozoic and Cenozoic eras.Considering the characteristics of the fitment of the South China Block with the northern margin of the South China Sea,the evolution pattern of the South China Sea Rift,and the tectonic movement of the plate,it can be seen that by comparing the features of the Sanshui Basin and the main and passive rifts,the reason for the early cracking of the Sanshui Basin is the hot source upsurges in the mantle and it is similar to the initial dynamism of the active rift.However,due to the thicker continental crust in the area of the Sanshui Basin,the size of the magmatic gush is limited and the splitting activity in the Sanshui Basin has not become the center of the subsequent expansion of the South China Sea,Sanshui Basin can be identified as abortive atypical active rift basin combined with the geochemistry of volcanic rocks.