Cenozoic extension to strike-slip transition in the Liaodong Bay Subbasin along the Tan-Lu Fault Zone, Bohai Bay Basin: New insights from stress field modelling

The NE-trending Liaodong Bay Subbasin (LDBS), a subunit of the Bohai Bay Basin (BBB), developed along the Tan-Lu Fault Zone (TLFZ) in eastern China. The LDBS is controlled by both extensional and dextral strike-slip fault systems and has an episodic evolutionary history, leading to a poor understanding of its tectonic origin. In this paper, through interpretations of seismic data and other geological and geophysical data, four best-fit finite element models were generated to reveal the tectonic development of the LDBS and the whole BBB. The deformation features predicted by the modelling results are consistent with the geological evidence. The modelling results revealed that the extension directions of the LDBS changed from WNW-ESE during the Paleocene-early Eocene, to NW-SE during the middle-late Eocene and then to NWN-SES or nearly N-S in the Oligocene and Miocene. The changes in the extension direction resulted in a strike-slip transition of the TLFZ in approximately the middle-late Eocene, from normal to dextral transtensional, and transformed the LDBS and the whole BBB from an extensional basin into a dextral transtensional basin. This transformation was likely triggered by the kinematic adjustment of the Pacific Plate from NNW to WNW in the middle-late Eocene, but was maintained and enhanced by the Indian-Asian collision during the rest of the Cenozoic.