Abstract: Dunhua-Mishan fault zone is the most important branch in the northern segment of Tancheng-Lujiang fault zone and its large scale of sinistral strike-slip shear age has been an unsolved scientific problem. The field structural and microstructural analyses suggest the Dunhua-Mishan ductile shear zone near Zhiyi Town, Mishan County is sinistral strike-slip shear zone ，the deformational temperature of which is about 450℃ to 650℃. The biotite ⁴⁰Ar/³⁹Ar isochron age, which is (161±3)Ma, was collected in the mylonite of ductile shear zones. If the age is combined with the age of Wandashan terrane strike-slip and matching accretion, it is considered that Dunhua-Mishan fault zone made the intense sinistral strike-slip movement in the last stage of J₂. The isochron age data show that the second left-lateral strike-slip age of Tancheng-Lujiang fault zone occurred during the period of tectonic movement in marginal-Pacific tectonic domain. It is also the age of Tancheng-Lujiang fault zone which stretches to the Northeast, China. The age of sinistral strike-slip movement of Dunhua-Mishan fault zone is identical with the age of Wandashan terrane strike-slip and matching accretion, which indicates that both are the product with the same tectonic background.

Key words: Tancheng-Lujiang fault zone, Dunhua-Mishan fault zone, ductile shear zones, mylonite, ⁴⁰Ar/³⁹Ar inverse isochron age