Abstract:

According to the numerical relationship between subsidence (or uplifting) rate and boundary fault strike-slip rate in pull-apart basin, the Cenozoic dextral strike-slip displacement of the middle portion of the Tan-Lu fault zone is indirectly calculated by restoring subsidence history of the Weibei sag which is bounded by the two branch faults of the Tan-Lu fault zone. The subsidence history restoration of four wells located at different structural units shows the sag experienced Early to Middle Paleogene fast subsidence, Late Paleogene uplifting and Neogene to present thermal subsidence,  and their averaged subsidence rate are  0.142 9 km/Ma, -0.072 8 km/Ma and 0.032 5 km/Ma respectively. Based on the analysis of the direction and velocity variation of the Pacific-Eurasia subduction, it is inferred the southwestward component of the westward compression stress between Pacific and Eurasia plate might be the main trigger for the dextral strike-slip movement of the Tan-Lu fault zone when the subduction direction changed from northwest to west at Middle Eocene (39.5 Ma). Given the strike-slip movement started at Middle Eocene and sustained to the present time, jointly considered with the subsidence and uplifting rate of the Weibei sag, the Cenozoic dextral strike-slip displacement of the middle Tan-Lu fault zone is calculated to be about 15 km.

Key words: strike-slip displacement, strata back-stripping, pull-apart basin, Weibei sag, Tan-Lu fault zone, structural geology