The end of ductile shear deformation of Ningshan fault: Constraint from the activity time of Longbozi shear zone

Three groups of ESR dating ages were obtained from different vein materials in Longbozi shear zone, i.e., 125.6~88.7Ma, 56.7~32.9Ma and 19.8~14.6Ma. The first type of vein materials sampled from schistosities and A-type fold cores marked the end of left-lateral shear deformation. It has been confirmed that the ductile deformation of Ningshan fault began from the early Late Triassic, and might have lasted to Early-Middle Jurassic. However, the result of the first type of vein material ESR dating shows that Ningshan fault left-lateral ductile shear effect lasted to Early Cretaceous. So Early Cretaceous was the critical period when the ductile shear deformation transformed to brittleness in Ningshan shear zone. Furthermore, Ningshan fault experienced Late Triassic-Middle Jurassic rapid-cooling phase, Late Jurassic-Cretaceous slow-cooling phase, and Paleocene-Quaternary rapid-cooling phase. The strain translation that occurred in the late slow-cooling phase suggests that Early Cretaceous also was the critical period of intracontinental deformation mechanism changing.