The Mantle Plume Model For The Evolution Of Bohai Bay Basin

Bohai Bay Basin has experienced strong Yanshan, Himalayan tectonic movement, resulting in the complex tectonic framework. The previous researchers have maintained different views on its formation. In this thesis, the mantle plume model is used to build the evolution framework of the Bohai Bay Basin, taking the Jiyang Depression and its cousins in the vicinity area as the examples. The author has studied the evolution history via basin analysis, tectonic-sedimentation analysis, seismic reflection profile, the fossil stress analysis, paleocurrent direction, clastic composition and tectonic setting and physical simulation etc.The mantle plume originated in Bohai Bay in the Jurassic, and started to control the evolution of the Bohai Bay basin in the Late Cretaceous. The processes can be divided into three phases: the thermal uplift (Late Jurassic～Paleocene), thermal stretch or thermal extension (Paleocene Ek～Es₂) and thermal subsidence (Es₁～Ng). The three phases correspond to different structural characteristics and sediment responses.Thermal uplift phase is characterized by the grabens controlled by high angle tension faults, and the rift shoulders initiated and rotated outward. The sub-synrift sedimentary beds formed in Jurassic and the beds formed in Cretaceous show two opposite wedges in the seismic reflection profile. During thermal extension, the intense extension occurred; the rift shoulders rotated in a wide margin and started to be suffered the erosion, becoming the main source areas. The basin uplift pointed to internal basin and developed widely detachment faults, having limited the ocean crust spreading. In thermal subsidence, the basin extension obviously decreased, accompanied by the surfacial tectonic inversion showing the beginning of post-rift thermal subsidence. The thermal subsidence was obviously weakened by the end of Dongying Formation (Ed), showing a the breakup unconformity between Dongying Formation and Guantao Formation (Ng/Ed).