Intracontinental deformation around the fixed tip of the continental-scale, strike-slip Tan–Lu fault zone in eastern China

Abstract

It remains unclear whether large-scale polyphase displacement along strike-slip faults is associated with tip propagation, and how the tip-damage zones of these faults respond to intracontinental block movements. Damage structures around the southern tip of the 2400 km long Tan–Lu fault zone (TLFZ) in eastern China provide an ideal opportunity to investigate deformation mechanisms at the tip of an intracontinental strike-slip fault. Structural and geochronological data from the southern Zhangbaling uplift within the TLFZ show that following the Triassic initiation of the fault, two phases of sinistral faulting occurred: an earlier phase at the beginning of the Early Cretaceous and later phase between the Early and Late Cretaceous. The early sinistral structures are expressed by ductile shear zones in the southern Zhangbaling uplift, whereas the younger sinistral structures are expressed as shear zones in the north and brittle faults in the south. Zircon U–Pb dating results for felsic gneiss of the TLFZ suggest that c. 200 km of cumulative displacement occurred during the Cretaceous and was restricted to wall rocks on the western side of the fault. The southern tip of the TLFZ remained fixed during the displacement, and the dilational quadrant associated with the fault is interpreted to have been stationary. The current c. 400 km of sinistral offset of the Dabie and Sulu orogens represents the original offset caused by the Triassic collision of the North China Craton and South China Block. The two phases of sinistral motion were induced by two phases of compression along the c. 460 km long contractional quadrant, which was dominated by thrusting along pre-existing faults as well as fault-related folding and uplift. Damage structures at the southern tip of the TLFZ show that large-scale polyphase strike-slip motion may be associated with a fixed fault tip, hundreds of kilometres of displacement can be restricted to one side of a major fault, and displacement can be accommodated by thrusting along pre-existing faults in the contractional quadrants. Supplementary material : LA-ICP-MS zircon U–Pb data for the felsic gneiss sample FD30 are available at https://doi.org/10.6084/m9.figshare.c.6368850