New insights into the provenance of Cenozoic strata in the Qaidam Basin, northern Tibet: Constraints from combined U-Pb dating of detrital zircons in recent and ancient fluvial sediments

Abstract

Determining the provenance of Cenozoic strata in the Qaidam Basin is key to understanding the basin-mountain coupling history in the northern Tibetan Plateau (TP). However, the specific source areas of Cenozoic strata in the northern Qaidam Basin remain highly debated. Here, we combine analyses of detrital zircons UPb geochronology for recent and ancient fluvial sediments from the northern Qaidam Basin to trace source areas of Cenozoic strata and reconstruct related mountain-building processes. The results indicate that the diagnostic 270–240 Ma zircon UPb peak, which was previously recognized as the unique input of a southern source area, is widespread in the recent fluvial sediments of the northern Qaidam Basin. Given our new zircon UPb data, the source-to-sink transport processes of Cenozoic sediments in the northern Qaidam Basin can be summarized as follows. (1) The northern Qaidam Basin has received the eroded detrital material from a dominantly northern source throughout the Cenozoic. (2) The Qaidam BeiShan was uplifted already at least by the early Eocene and served as the single contributor of detritus to the Dahonggou (DHG) region, suggesting that far-field stress due to the India-Asia collision had been propagated to this region as early as the early Eocene. (3) An abrupt change in provenance is observed in the DHG region during 46.5–43.7 Ma. We interpret this middle Eocene source change as reflecting the onset of growth of the North Altyn Tagh Range, implying that the North Altyn Tagh Range was already serving as an important source area for the DHG region by the middle Eocene. (4) The South Qilian Range served again as the dominant source area for the DHG region after 24.6 Ma. The shift in provenance from the North Altyn Tagh Range to the South Qilian Range can be attributed to the uplift of the Saishiteng Shan.