Initial movement of the Karakorum Fault in western Tibet: constraints from SHRIMP U-Pb dating of zircons

The Karakorum Fault zone (KFZ) plays an important role in understanding the formation, evolvement and deformation of the Tibetan Plateau. The high-Tdextral shearing metamorphic rocks, e.g., mylonites or mylonitized gneisses-granites, locally crop out along the southeastern part of the KFZ in the Ayila Ri'gyu Range area. The SHRIMP U-Pb dating of the syn-kinematic crystallized zircons indicates that the initial age of the KFZ is similar to 27 Ma, similar to 10 Ma older than previous results. The extensive high-T dextral shearing along the KFZ started at least at 27-20 Ma, accompanied by the syn-kinematic emplacement of leuco-granites. Deformation and concomitant fluid circulation during shearing most likely occurred as early as at 25-13 Ma. The KFZ probably grew from southeast to northwest along the fault as a result of continuous convergence between the India plate and Eurasia plate.