Neoproterozoic Sedimentary Evolution And Its Tectonic Significance In The Northwestern Margin Of Tarim Basin

The Neoproterozoic period was a very important stage in global tectonic evolution,which underwent the assembly and breakup of Rodinia supercontinent.As one of the three most important cratonic basins in China,the Neoproterozoic sedimentary system of the Tarim Basin recorded a great deal of information about the tectonic evolution of Neoproterozoic,and it is also the focus of deep oil and gas exploration in the cratonic basin of China.Based on the detailed field geological profile survey and systematic zircon U-Pb chronology analysis,this paper focuses on the Neoproterozoic sedimentary filling sequence and clastic zircon provenance characteristics with a view to revealing the sedimentary evolution process of Neoproterozoic basin and further discussing the basin prototype,tectonic attribute and basin formation mechanics of Neoproterozoic basin in the northwestern margin of Tarim basin.The sedimentary sequence from Nanhua to Sinian in Tarim Basin is characterized by continental rift sedimentary formation.Overall,The Nanhua system is a multi-cycle sedimentary formation controlled by continuous episodic rifting and glaciation.From the Xifangshan Formation to the Yuermeinak Formation,the Nanhua System developed fast-filling turbidite sedimentary formations controlled by rifting,and recorded glacialwater facies sedimentary formations formed by multi-stage glaciation.Meanwhile,this paper identifies the syndepositional deformation records of liquefied carbonate veins,seismic fractured rocks,seismic collapsed rocks,small normal faults and collapsed folds related to fault activities.From Sugetbrak Formation to Qigebrak Formation,the Sinian system transformed from clastic rock formation to marine carbonate sedimentary formation,and the basin evolved from rift stage to depression stage,finally formed a wider intracontinental depression basin.The transformation from Nanhua to Sinian is a continuous sedimentary process from continental clastic rocks to shallow marine carbonate rocks,which reflects the rising process of lake or sea level and coincides with the continuous subsidence process of basin evolution from rift to depression.The U-Pb dating results of detrital zircons show that the Xifangshan Formation of Nanhua System in the northwest of Tarim Basin is dominated by 2600-2100 Ma,2050-1700 Ma and 950-720 Ma age groups.The age of detrital zircons in Sugetbrak Formation of Sinian System is mainly composed of 2700-2300 Ma,2100-1800 Ma,900-720 Ma and 700-600 Ma four age groups,which is consistent with the records of magmatism and metamorphism in the northern margin of Tarim Basin.It indicates that the clastic material may come from the northern edge of tarim basin itself.Combined with the comparative analysis of clastic zircon age spectrum of other continents,the results show that the Tarim,South China and Northern India plate have similar age groups,indicating that these blocks underwent similar tectonic-magmatic events in the Precambrian period.