Structural Deformations And Their Geochronology Of The Nalati Range In Yili,Xinjiang

The Nalati Range is located in the south of Yili basin,Xinjiang,and the southern margin of the Middle Tianshan massif.The late Proterozoic,early Palaeozoic and late Palaeozoic strata,granite and mylonite have been outcropped in this area,which have experienced the superposition and transformation of multiple periods of magmatism and tectonic deformation,resulting in its extremely complex structure.Nalati Range is an important structural belts to reveal the tectonic evolution of the Tianshan area.At present,the research degree of the Nalati Range structural zone is relatively low,and there are still intense dabates in the directions,ages and stages of structural deformations.Based on the study of the characteristics of the structural deformation and chronology of the crossection of the Nalati Range,this paper provides new evidences and ideas for the tectonic evolution of the Tianshan Mountains.Through field survey,measurement and microstructural discrimination of rock slices,the characteristics of rock deformation and their levels and stages in the Nalati Range are summarized.Data from zircon SHRIMP U-Pb method,Ar-Ar dating method and previous research results were used to determine the time of tectonic deformations.According to the regional tectonic background,the tectonic evolution model of the Nalati Range is reconstructed.Through the study of this paper,it is proposed that there are four stages of structural deformations in the Nalati Range,which have the following deformation characteristics:(1)Late Proterozoic stage,occurred between 950 Ma-900 Ma,the development of the eyeball granitic mylonite at this stage,the product of ductile rheology under the action of high temperature,appeared at the core of the Nalati Range,showing the deformation characteristics of the south to north thrust,corresponding to the polymerization of the Rodinia continent;(2)Silurian-Devonian stage,occurred between 430 Ma and 360 Ma,which developed tightly closed diagonal fold and axial cleavage,which mainly developed in the south of the late Proterozoic core and the south of the Carboniferous Dahalajunshan Formation.This stage corresponded to the southward subduction of the North Tianshan ocean.(3)Carboniferous-Early Permian stage,occurred between 330 Ma and 280 Ma,which developed ductile-brittle folds and reverse faults that dip northward,mainly developed in the Palaeozoic intrusive body and the interior of the volcanic rocks of Dahalajunshan Formation,corresponded to the subduction of South Tianshan ocean northward and the eventually collision with the Middle Tianshan block.(4)Late Permian-Early Triassic stage,occurred at 260 Ma-240 Ma.At this stage,“X” joints and nearly vertical faults can be observed,corresponding to the intracontinental deformation and the strike-slip adjustment after the collision.