Two-stage expansion of the South Qilian Shan during the mid-Miocene: Insights from provenance analysis in the northern Qaidam Basin, NW China

The remote effects of the collision between India and Eurasia since the Cenozoic have led to complex tectonic deformation patterns in the northern Tibetan Plateau. The thick Cenozoic strata in the Qaidam Basin, located in the northern Tibetan Plateau, record comprehensive information about this process. This study combines detrital zircon U-Pb geochronology, heavy mineral analysis, and paleocurrent analysis along the Lulehe section and modern rivers in the northern Qaidam Basin to characterize sediment provenance shifts. The modern river debris suggests that the sedimentary fill in the northern Qaidam Basin mainly comes from the pre-Cenozoic basement and the Neoproterozoic basement that is now exposed in and around the South Qilianshan. The detrital zircon grains from the Lulehe section primarily have ages corresponding to the early Paleozoic (400-500 Ma), Neoproterozoic (700-900 Ma), Paleoproterozoic (1500-2100 Ma), and Neoarchean (2500-2800 Ma). The age composition of detrital zircon in the Lulehe section significantly deviates from other representative sections in the northern Qaidam Basin, primarily due to a notably higher abundance of Neoproterozoic detrital zircon grains that have rarely been documented regarding their provenance. Sandstone samples heavy mineral provenance shows clear spatiotemporal variations. These results suggest four provenance shifts in the Cenozoic strata in the northern Qaidam Basin. These shifts were associated with two phases of significant topographic growth in the South Qilian Shan. During the first phase, the South Qilianshan underwent tectonic uplift and provided clastic materials to the Qaidam Basin at ca. 31 Ma. Then, the Saishiteng-Aolaoshan in the northern basin experienced two stages of topographic growth at ca. 27 and 21 Ma and became one of the sediment sources. In a later phase, the Qilianshan experienced large-scale synchronous tectonic uplift at ca. 15 Ma, and the modern landforms and water system pattern in the northern Tibetan Plateau were formed at this time.