Cenozoic Post-Rift Unconformity and the Accelerated Subsidence Events of the Jiyang Depression, Bohai Bay Basin and Preliminary Analyses on their Original Mechanism

To investigate the events of post-rift unconformity and accelerated subsidence in the Cenozoic Jiyang Depression, Bohai Bay Basin, and discuss on their original mechanism, a forward model of flexural cantilever model and a reverse model of 2-D flexural backstripping model were employed to rebuild the Cenozoic tectonic evolution of two seismic lines trending in NS in the Jiyang Depression. The forward modeling showed that, to rebuild the geometrical structures of the two lines at 14 Ma, uplift events that produced sgn-rift and post-nift unconformities should be included in the model, and the uplift amplitude in the northeast is higher than in the southwest. While the reverse modeling showed that the amount of the thermal subsidence, based on the stretching factors deduced from the faults, is not enough to restore the paleo-bathymetry at 14 Ma. Excess subsidence should be added, and the amplitude of the excess subsidence in the northeast should be larger than in the southwest. The results suggest that during the development of the Jiyang Depression, The lithosphere might be thinned not only passively by horizontal extension, but also thinned actively by some vertical factors; and the accelerated subsidence since 14 Ma has a trend of propagating from the northeast to the southwest. The analyses also indicate that, in addition to the passive factor of horizontal extension, by which the asthenosphere was perturbed thermally and then experienced quick thermal decay, some other active factors, such as lithosphere delamination and mantle lithosphere metasomatism, can be candidate mechanism for the post-rift unconformity and the accelerated subsidence.