The onset of the Tan-Lu fault movement in eastern China: constraints from zircon (SHRIMP) and 40Ar/39Ar dating

In eastern China, the Dabie Shan-Su-Lu orogenic belt has been separated by the Tan-Lu sinistral strike-slip fault. Mylonites are exposed along the strike-slip fault system in the southern segment, and along the eastern margin of the Dabie Shan orogenic belt. The country rocks of the mylonites are retrograde UHP eclogites, gneissic granites, muscovite granites and gneisses. The ductile strike-slip shear zone trends 30-40 degrees N (NE30-40 degrees-trending) and exhibits stretching lineations and nearly vertical, SE-dipping foliations. Most of the zircon grains separated from mylonites have a weighted average radiometric age of 233 +/- 6-225 +/- 6 Myr. These data constrain the onset of the Tan-Lu sinistral strike-slip movement and imply that the Tan-Lu sinistral strike-slip motion developed after retrograde UHP metamorphism. The related phengite within the eclogite rocks on the western side of the Tan-Lu fault, with 40Ar/39Ar plateau ages of c. 182-190 Myr, is also deformed and aligned parallel to the almost NE trending stretching lineations. Non-metamorphosed granites exhibit sinistral strike-slip shearing and indicate that the Tan-Lu fault initially developed after 182-190 Myr. Muscovite collected from the mylonite yields 40Ar/39Ar plateau ages of 162 +/- 1-156 +/- 2 Myr. The zircon SHRIMP age data, the muscovite 40Ar/39Ar plateau ages, together with structural and petrological field information support the interpretation that the Tan-Lu strike-slip fault was not related to the Yangtze-north China plates collision, but corresponded to the formation of a NE-trending tectonic framework in eastern China starting c. 165-160 Ma.