Structural patterns and ages of Permian-Triassic multistage strike-slip faulting in the Chifeng area, southeastern Inner Mongolia, China: Implications for the final closure of the Paleo-Asian Ocean

The closure of the Paleo-Asian Ocean (PAO) to the north of the North China Craton (NCC) holds significance in comprehending the Phanerozoic continental evolution of East Asia. However, the timing of the final closure of the PAO, tectono-magmatic records of this process in the northern margin of the NCC, and related geodynamics remain to be resolved. Here we undertaken detailed macro- and micro -structural investigations on the E -Wstriking and NNE -striking fault system in the Chifeng area, northern edge of the NCC. Combined with new zircon U-Pb and muscovite 40Ar/39Ar dating, we delineated three phases of strike -slip faulting in the research region during the Permian -Triassic, including WNW -ESE -striking and NE -SW -striking ductile sinistral shearing at270-258 Ma and 258-246 Ma, respectively, and subsequent - E -W -oriented ductile-brittle dextral shearing at230-209 Ma. Based on analysis of paleotectonic stress fields, we propose that the first two -stage deformation shared a regional unified N -NNE contractional setting, while the late - E -W -striking dextral shearing reflected a distinct regional NNW -SSE shortening event. The regional magmatism reveals three age peaks of - 270 Ma, -250 Ma and - 230 Ma, corresponding well to the above three-phase deformation. Further, zircon Hf isotopic data imply that the composition of juvenile material in regional deep-seated crust gradually increased from Permian to Triassic. The N -NNE contraction may be controlled by the eastward scissor-like final closure of the PAO during the Middle Permian -Early Triassic. The middle -late Late Triassic NNW -SSE contraction is likely influenced by the remote effect of the low -angle southward subduction of the Mongol -Okhotsk oceanic plate.