Evolution of Paleozoic West Junggar Basin, NW China: Seismic data, detrital zircon evidence from Earth’s oldest alkali lake deposit

The Permian Fengcheng Formation of the Western Junggar region in the Southwestern Central Asian Orogenic Belt (CAOB) represents one of Earth’s oldest alkali lake deposits. Here, we present a comprehensive study of the stratigraphy, petrography, two-dimensional seismic data, U–Pb geochronology, and Hf isotope analysis of detrital zircons of this deposit. The results, in conjunction with published data, reflect the tectonic evolution of southwestern CAOB. The ages of detrital zircons indicate that the Fengcheng Formation deposition is inferred to have concluded the early Permian Kungurian. The Hf isotopes of detrital zircons indicate that the detritus for the Fengcheng Formation was derived from upper crustal magmatic sources. The West Junggar Basin preserves the records of three Paleozoic tectonic stages. The first stage occurred in the Early Paleozoic and involved intraoceanic subduction and arc-continent collision. The second stage involved the Carboniferous closure of the Junggar Ocean following successive filling of oceanic basins. The final stage occurred in the Early Permian and was related to intracontinental rifting and tectonic inversion. The results of comparing the comprehensive data of U–Pb ages and Hf isotopes of 2537 zircons from West Junggar, Tianshan and Altay show that the orogenic belts to the south of the CAOB experienced similar plate kinematics and vertical crustal growth in the Paleozoic.