Timing of the formation of the Sangshuyuanzi ductile shear zone in the central segment of the South Tianshan and its tectonic significance

Abstract：The Sangshuyuanzi ductile shear zone in the central segment of the South Tianshan is an east-west-trending shear zone, in which foliations, lineations and asymmetric structures are well developed. Based on a kinematic analysis,the authors think that the Sangshuyuanzi ductile shear zone is of sinistral strike-slip nature. 40Ar/39Ar dating of muscovites from mylonite in the shear zone yields a plateau age of 393±6 Ma and an isochron age at 389±3 Ma. 40Ar/39Ar dating of biotites from en-echelon fractures in the zone gives a plateau age of 366.5±2 Ma and an isochron age of 365.0±3 Ma. According to the above-mentioned study, combined with the regional tectonic background, this paper suggests that the Sangshuyuanzi ductile shear zone is a syncollisional strike-slip tectonic zone formed by oblique collision between the Tarim plate and the Kazakhstan-Ili plate, which resulted in strain partitioning parallelly to the boundary of the two plates.