Age and structural deformation of ductile shear zones on the southern margin of the East Kunlun Mountains

As a result of oblique subduction of the Bayan Har-Songpan-Garze terrane toward the East Kunlun terrane in Mesozoic, a major ductile shear zone formed along the southern margin of the East Kunlun terrane.Ductile deformation phenomena observed in the ductile shear zones, such as porphyroclasts, porphyroclastic structure, cleavage-step, mica fish, S-C fabric, asymmetrical folds and echelon veins, implying both dextral and sinistral shear characteristics.The dextral shear is earlier than the sinistral shear.Howev-er, the sinistral shear is the dominant feature in these ductile shear zones.LA-ICP-MS U-Pb dating of zircons from the mylonitiza-tion granite in Xidatan and the undeformed granite in Xiaonanchuan yielded ages of 199.3±2.2 Ma and 196.4±1.3 Ma, respectively.Zircons dated here are typically formed via magma crystallization, which means that their ages could represent the emplacement time of the two plutons.The deformation degree of the two pluton, which is completely different from each other, indicates that the southern margin of the East Kunlun left-lateral ductile shear zone should have formed in 199~196 Ma.