Abstract:Generally ductile shear zone (DSZ) is a combination of simple and pure strain. The only difference is which factor (simple shear or pure shear) plays a significant role. With this theory, decomposing the strain and defining shearing types are very effective in quantitative study of a ductile shear zone. Two common methods of kinematic vorticity (Wk) measurements, the polar Mohr diagrams and quartz c-axis fabrics were applied for the first time in the Xaitongmoin-Quxu ductile shear zone, which show the similar results with uncertainties. By means of nine mylonitic samples analyzed with the polar Mohr diagram, the analyzed results suggest that kinematic vorticity ranges from 0.73 to 0.96, mean value Wk around 0.83. In addition, according to polar Mohr diagrams, we calculated the thinning ratios (S) of the shear zone, showing that the thinning ratio ranges from 0.09 to 0.35, with a mean value around 0.20. We also calculate the kinematic vorticity of the four samples through the quartz c-axis fabrics and strain ratio method, and the results show that Wk ranges from 0.85 to 0.93, with a mean value Wk around 0.88. Above integrated results of kinematic vorticity analyses indicate that the Xaitongmoin-Quxu ductile shear zone is general shear.The results show that the simple shear plays a dominate role in assessing formation mechanism of the Xaitongmoin-Quxu shear zone, which should be related to the tectonic transition of the Lhasa terrain from tectonic compression to extension during Miocene. The structural deformational characteristics and kinematic vorticity determines the tectonic evolution process of the Gangdese region and further advances geologic studies of the middle-south Tibetan plateau.