Structural model and Cenozoic kinematics of Tan-Lu deep fracture zone in Bohai Sea area

Abstract：The Tan-Lu DFZ (deep fracture zone) stretches from Lujiang (in Anhui) through Tancheng, Yishui and Anqiu (in Shandong) to Bohai Sea area where it is covered by Cenozoic basin sedimentary layer and sea water. Judging from the regional gravity-magnetic field map, Tan-Lu DFZ in the Bohai Sea area lies along the Laizhou Bay—eastern Bohai Sea—Liaodong Bay line, generally striking NNE, parallel to the eastern limb of the mantle rise in the Bohai Sea. The Cenozoic basin in the Bohai Sea resembles a mirror image of the mantle rise. The boundary faults of the Paleogene rifting sub-basins are developed in multiple directions, dominantly striking NE, NNE, NEE, NW, NWW, and mostly showing characteristics of listric normal faults in terms of geometry and kinematics. 2 to 4 steeply dipping NNE-trending basement strike-slip faults developed along the Laizhou Bay—eastern Bohai Sea—Liaodong Bay line constitute a right-lateral strike-slip structure with their associated structural deformation, and the location is approximately consistent with the Tan-Lu DFZ interpreted by the regional gravity-magnetic field map. In combination with the characteristics of deep crust structure and Cenozoic basin structure, the authors have reasons to believe that the structural model of Tan-Lu DFZ in Bohai Sea area is a vertical strong deformation zone at the crust scale, which is composed of the NNE-trending right-lateral strike-slip zone in Cenozoic basin and the deep faults cutting the Moho surface. However, the Tan-Lu DFZ is not a simply right-lateral strike-slip zone. Extensional faults controlling Paleogene fault sub-basin might have utilized the fault surface in shallow crust of the deep fracture zone, and could have been detached in middle crust layer during extensional displacement; nevertheless, the right-lateral strike-slip displacement of the deep fracture zone was likely to cause the connection between the shallow fault and the deep fault.