Middle Jurassic intracontinental evolution of East Asia: Insights from the Tianshifu-Dongyingfang basin of the Liaodong Peninsula, NE China

The Middle Jurassic intracontinental shortening event in East Asia, known as episode A of the Yanshanian Movement in the eastern North China Craton and the first phase of the Daebo Orogeny in the Korean Peninsula, respectively, has been thoroughly studied during the past two decades. However, the timing of its beginning, duration, and deformational processes are still highly controversial because few studies have probed the correlations between episode A of the Yanshanian Movement and the first phase of the Daebo Orogeny. The Tianshifu-Dongyingfang basin, located in the northern Liaodong Peninsula, is filled with complete Jurassic sequences that can be compared with those in the eastern North China Craton to the west of the Tan-Lu fault zone and the Korean Peninsula. Regional stratigraphic correlations suggest that the Tianshifu-Dongyingfang basin contains not only the syntectonic conglomerates, but also the lower and upper unconformities A₁ and A₂ of episode A of the Yanshanian Movement, which separated the syntectonic conglomerates from the underlying Early−Middle Jurassic coal measures and the overlying Late Jurassic red beds, respectively. Detailed field survey and structural analysis show that the development of syntectonic conglomerates and unconformities A₁ and A₂ were controlled by the imbricate thrust fault system in the basement, which resulted from the WNW−ESE compression inversed from the fault-slip data. The youngest detrital zircon U-Pb ages obtained near unconformities A₁ and A₂ show that the WNW−ESE compression of episode A of the Yanshanian Movement in the Liaodong Peninsula initiated at ca. 171 Ma and ended at least by 163 Ma. Our new structural and geochronological data, combined with data from the neighboring areas, suggest that episode A of the Yanshanian Movement and the first phase of the Daebo Orogeny belong to a single intracontinental shortening event, the compressional deformation of which was derived from the westward, low-angle subduction of the Paleo-Pacific plate and transmitted to the Korean and Liaodong Peninsulas at ca. 172−170 Ma and to the eastern North China Craton to the west of the Tan-Lu fault zone at 170−165 Ma.