Deformation Characteristics And Evolution In The Area Aroud The Southern End Of The Tan-Lu Fault Zone

The deformation characteristics around the southern end of the Tan-Lu fault zone reveal close evolution relation between the Tan-Lu Fault Zone and the Dabie orogenic belt. The deformation evolution can be subdivided into four stages. The first stage of deformation (D1) corresponds to the early deep subduction stage of the orogenic belt in the Middle Triassic. The main structures of the first stage are the E-W folds in the southern foreland, indicating N-directed subduction of the Yangtze Plate beneath North China Plate. Deformation structures of the first stage have not been preserved inside the Dabie orogen. The second stage of deformation (D2) occurred during the late deep subduction of Middle Triassic when the Tan-Lu Fault Zone occurred as an intra-continental sinistral transform fault zone that caused sinistral offset of the Dabie and Sulu orogenic belt. Folds in the eastern foreland were changed into NE-NEE trends. The NE-SW trending Zhangbaling complex is representatives of the Tan-Lu sinistral strike-slip ductile shear zone along the southeastern margin of the Dabie orogenic belt. The shear zone dips SW steeply, shows NW-SE mineral lineation, and is significantly different from exhumation structures in the Dabie belt. Main deformation structures in the Dabie belt during the exhumation stage (D3), Middle Triassic to Middle Jurassic) consists of a NW-SE lineation with consistent top-to-the-NW sense of shear. Extrusion direction of the orogenic exhumation is perpendicular to the Tan-Lu Fault Zone. The Tan-Lu ductile shear zone stayed in brittle deformation domain when the exhumation took place. The exhumation resulted in NW-ward thrusting of the foreland over the shear zone and NW-ward thrusting of the shear zone over the orogenic belt. A NW-directed arcuate fold-thrust belt appeared around Taihu, which bent the earlier Tan-Lu ductile shear belt into E-W locally and caused the foreland folds into almost completely parallel to the Tan-Lu Fault Zone. During the oblique exhumation, the Xiangfan-Guangji Fault Zone acted as a lateral, dextral strike-slip boundary that caused previous E-W folds in the southern foreland into NW-SE trends. The last stage of deformation (D4) in the area happened during Late Jurassic when brittle sinistral faulting took place along the earlier thrusts on the both sides of the earlier Tan-Lu ductile shear zone. The D4deformation also caused brittle thrusting along the Xiangfan-Guangji Fault Zone and a series of thrusts in the foreland. The NE-directed brittle thrusting along the Xiangfan-Guangji Fault Zone is coeval with brittle sinistral faulting of the Tan-Lu fault zone, and represents initiation of the circum-Pacific tectonic regime.The structural characteristics around the southern end of the Tan-Lu Fault Zone show that it ends on the southeastern margin of the Dabie orogenic belt near Wuxue city north of Yangtze River. The Tan-Lu Fault Zone, initiated as an intra-continental transform fault zone, did not extend further south of the Dabie orogenic belt during the collision of the North and South China plates. Its sinistral displacement during the second faulting was converted into thrusting and shortening in the foreland. This pattern of deformation belongs to end structures of a wrench fault, and leads to its not further extension south of the Dabie orogenic belt.