Sr-Nd-Pb Isotopic Compositions of the Neogene Eolian Deposits in the Xining Basin and Implications for Their Dust Sources

摘要

The Neogene eolian deposits in the Xining Basin are valuable archive for studying the evolution of the Asian monsoon system and geomorphic processes of Northwest China. The Neogene eolian deposits that paleomagnetically dated at about 14 Ma probably were sourced from the middle and west Qinghai-Tibetan Plateau(QTP) as indicated by elemental compositions and magnetic properties. This study provides the Sr-Nd-Pb isotopic ratios of different sediments(gravels from the river terraces, Neogene eolian deposits and Quaternary loess) in the Xining Basin. The results show that:(1) Sr-Nd isotopic compositions of terrace gravels are different from those of the Neogene and Quaternary eolian deposits, although the Nd isotope ratios of gravel on the 10 th terrace(T10) and eolian deposits are similar.(2) Pb isotopic compositions of river gravels are obviously different from the eolian deposits in the Xining Basin. However, Pb isotopic compositions of eolian deposits in the basin are similar to those of eolian deposits in the central Chinese Loess Plateau.(3) Sr-Nd-Pb isotope results indicate that the Neogene eolian deposits in the Xining Basin were probably sourced from remote areas outside of the basin by long-distance transportation. The Qaidam Basin is probably an important source area for the eolian deposits in the Xining Basin.