The tectonic evolution in the North China basin

The North China basin is located within the North China craton on the northeastern coast of China, east of Beijing. The basin has been a focus of the oil industry for decades because it produces 50% of China's hydrocarbons. Despite extensive seismic imaging for exploration, complex deformational overprinting has obscured the origin of the basin and the tectonic evolution of this region. A popular view about the formation of the basin is that it is a pull-apart basin formed by a large right lateral strike-slip fault, the Tanlu fault. The Tanlu fault was originally a left lateral strike-slip fault formed during the convergence between the South China plate and the North China craton. Its reactivation and the change of its slip direction were possibly caused by the convergence of the Philippine plate (or Pacific plate) to Eurasia. The large earthquakes (>500 km deep) in 1999 and this year at the very northeastern end of the North China Basin suggest that converging plates can affect the far inland region around the basin. Based on recent study of seismic, well logging and magnetic data, we propose that at least four episodes of deformation have affected the basin. The first episode corresponds to a contractional event in the Middle to Late Mesozoic, with fold-thrust belt structures striking in a NW-SE direction. Second, an extensional system formed between Late Mesozoic and Early Tertiary time, with normal faults striking in the same direction as the previous contractional structures. Third, an Early Tertiary extensional system trends almost perpendicular to the compressional system in a NE-SW direction and post-dates earlier normal faults. Finally, an en-echelon strike-slip system, still active at present, is localized in Liaodong Bay, the northeastern part of the North China basin. The early fold-thrust structures in this region may be related to a widespread intracontinental contractional event observed elsewhere in the North China craton, immediately followed by extension related to gravitational collapse of the mountain belt. The overprinting of the later 2 extensional systems has produced a rhomboidal basin geometry that appears to be a pull-apart geometry, although the structures that produced this geometry formed at discrete times in the basin's history.