Structural architecture and tectonic evolution of the Cenozoic Zhanhua Sag along the Tan-Lu Fault Zone in the eastern North China: Reconciliation of tectonic models on the origin of the Bohai Bay Basin

摘要

The Zhanhua Sag, a major depocenter within the larger Bohai Bay Basin (BBB) along the Tan-Lu Fault Zone (TLFZ) in the eastern North China, developed through two successive phases with different stress regimes during the Paleogene. The kinematics and the slip history of the NW-SE- and N-S-striking normal fault systems strongly controlled the internal structure and stratigraphy of the Paleocene-Lower Eocene strata in the Zhanhua Sag during Phase 1. Isopach maps of the Paleocene-Lower Eocene stratigraphy show similar to 4000-in-thick elastic rock sequences in these structurally controlled depocenters. The average dip-slip rates of the NW-SE- and N-S-striking faults were 78.96 and 50.82 m/m.y. (respectively) in the Paleocene-Early Eocene, but decreased to 45.87 and 35.81 m/m.y. in the Middle-Late Oligocene. The NE-SW-striking fault systems and their slip history controlled the development of the Middle Eocene-Oligocene depocenters and their strata during Phase 2. The average dip-slip rate of the NE-SW-striking faults was 10.47 m/m.y. in the Paleocene-Early Eocene but increased to 93.49 m/m.y. in the Middle-Late Oligocene. The NE-SW-oriented faults cut across and displace the NW-SE-striking faults, indicating their relatively younger ages. These fault patterns and kinematics recorded in the Zhanhua Sag reflect an abrupt change in extension directions from ENE-WSW to NW-SE before and after the Middle Eocene that was related to a reversal in the slip direction from sinistral to dextral along the TLFZ. This slip reversal was, in turn, a result of a major change in the subduction direction of the Pacific Plate beneath eastern Asia and in the mode of strain partitioning across the TLFZ in the continental upper plate.