Detrital zircon U-Pb dating and geochemistry of the Paleogene-Neogene sediments in the Qaidam Basin (China): Implications for provenance and tectonics

Provenance analyses provide valuable insights into both the complex interaction between orogenic belts and surrounding sedimentary basins and the role of plate collision in the basin-mountain coupling process. This paper investigates the provenance of the Cenozoic sediments filling the Qaidam Basin (Qinghai Tibetan Plateau, China) by combining petrology, major elements, trace elements, rare earth elements (REEs), and Zircon U-Pb dating analysis to provide new insight about the collision of the Indian and Asian plates. The petrographic analysis indicates that the studied sediments are poorly sorted and made of angular to subrounded clasts, suggesting deposition relatively near to the source area. The Chemical Index of Alteration (CIA) of the samples in the study area, which ranges from 68.88 to 74.08, indicates that the study area experienced moderate weathering from the early Eocene to the early Miocene. In addition, Zr/Sc versus Th/Sc shows that most samples did not experience recycling. K2O/Na2O, SiO2, Th, Sc, Zr, La and Co contents indicate that the Cenozoic sediments filling the Qaidam Basin derived mainly from an active continental margin and a continental island arc setting. U-Pb dating of detrital zircons denotes that the studied sediments were derived from rocks with five major sets of ages (200-350 Ma, 350-500 Ma, 500-1000 Ma, 1000-1500 Ma, and > 1500 Ma), with the two first sets being more common. Based on the regional geology, therefore, these ages indicate that the main provenance source was shifted southwards from the Mesozoic crystalline basement (south Qilian Mountains) in the earlymiddle Eocene, to the Saishiteng Mountains in the middle-late Eocene, and to Lvliang and Qilian Mountains during the late Eocene-early Miocene. Zircon dating also indicates that the main source area was displaced eastward through time. Finally, it is concluded that the tectonic deformation progressed from west to east in the northern margin of the Qaidam Basin, reflecting a far-field response to the onset of the India-Asia collision.