Studies on 40 Ar/ 39 Ar thermochronology of strike-slip time of the Tan-Lu fault zone and their tectonic implications

Samples of mylonite, ultramylonite and phyllonite were collected from 5 localities in the Anhui part of the Tan-Lu fault zone for 40 Ar/ 39 Ar chronological studies. Among them 4 samples from 3 localities on the eastern margin of the Dabie orogenic belt yielded 40 Ar/ 39 Ar plateau ages of 128 —132 Ma; and 2 samples from the western margin of the Zhangbalin uplift and eastern margin of the Bengbu uplift gave the same 40 Ar/ 39 Ar plateau ages of 120 Ma. Isochron analyses and other lines of evidence suggest that the data are reliable. The data are interpreted as cooling ages of sinistral strike-slip deformation of the Tan-Lu fault zone. The younger ages from the north might be related to slower strike-slip rising. These results indicate that the large-scale left-lateral displacement in the Tan-Lu fault zone took place in the Early Cretaceous, rather than in Late Triassic (Indosinian) as proposed by some geologists. Therefore, this fault zone is an intracontinental wrench fault rather than a transform fault or suture line developed during formation of the Dabie orogenic belt.