Provenance identification for the Honggou section of the Qaidam basin in the northeastern margin of the Tibetan Plateau and its tectonic significance

Located in the northeastern corner of the Tibetan Plateau, the Honggou section deposits comprise thick Cenozoic strata, the provenance analysis of which provides an exceptional opportunity to study the uplift and denudation history of the potential source regions for the Qaidam Basin and the deformational processes in the northeast Tibetan Plateau. Here, the detrital zircon U-Pb ages and Hfisotopic compositions are used to trace the source changes for the Late Oligocene-Pliocene strata based on the magnetostratigraphy of the Honggou section. Most of the U-Pb ages of the detrital zircon from 23.7~12.5 Ma are concentrated within the intervals of 220~290 Ma, the εHf(t) is concentrated at -13.53~9.27, and the range of the tDM(Hf) is 524~1456 Ma. For zircons whose U-Th age are greater than 300 Ma, the εHf(t) is between -31.77 and 13.44, of which 76.3% is negative, and the Hf isotope tDM is between 484 and 3727 Ma. The zircon U-Pb ages of sandstone samples from 12.5~7.6 Ma are mainly concentrated at 400~500 Ma (peak ~ 440 Ma), 90% of the εHf(t) value (-27.75~10.75) is negative, Hf isotope one-stage model age is between 615~2115 Ma. Sandstone samples of 6.8~5.5 Ma, zircon U-Pb age is mainly distributed at 400~500 Ma, the εHf(t) value is ranging from -26.8 to 8.97, and the tDM is between 668~2093 Ma, but the zircon ages of 220~290 Ma increase significantly, having εHf(t) values ranging from -11.86 to 9.42, Hf one-stage model age range is 549~1399 Ma. Comparing these with neighboring tectonic units, we found that Hf isotopic compositions of zircon whose populations are at 220~290 Ma have affinity with the East Kunlun Shan, while the Hf isotopic composition of 400~500 Ma zircon is similar to South Qilian Shan. These features reveal that the East Kunlun Shan began to deform and become the main source region of the Qaidam Basin at 24Ma. The southward expansion of the Qilian Shan is at ~12 Ma, providing detrital materials for the Qaidam Basin and becoming the tectonic and geomorphic margin along the Tibetan Plateau. © 2020, Science Press. All right reserved.