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Geochemical Characteristics of Eolian Deposits on the Eastern Margin of the Tibetan Plateau and Implications for Provenance
Author(s) -
QI Lin,
QIAO Yansong
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12249
Subject(s) - provenance , aeolian processes , paleosol , loess , geology , geochemistry , plateau (mathematics) , sedimentary rock , loess plateau , geomorphology , soil science , mathematical analysis , mathematics
Eolian dust deposition is intimately related to atmospheric circulation and environmental setting of the source region, and therefore is an invaluable tool for studying the evolutionary history of atmospheric circulation patterns and paleoclimatic change. Identifying the provenance of any eolian deposit is crucial not only for reconstructing the paleoenvironmental history of the dust source region, but also for understanding the paleoclimatic significance of various indices. Loess and paleosol samples from the Garze region on the eastern margin of the Tibetan Plateau (TP) were analyzed for their elemental (major and trace elements) and isotopic (Sm‐Nd) geochemistry and compared with those of Northern Chinese (NC) loess formed at the same age. The results show that the geochemical compositions of the Garze loess and paleosol samples are similar to those eolian deposits on the Chinese Loess Plateau (CLP), and also resemble the average UCC. This indicates that the eolian deposits on the eastern margin of the TP were derived from well‐mixed sedimentary protoliths that had undergone numerous upper crustal recycling processes, just as with the CLP loess deposits. However, compared with NC loess, the Garze samples have higher ΣREE, Li, Rb, Zr, Cs, Hf and Bi concentrations, higher TiO 2 /Al 2 O 3 , Hf/Nb, La/Nb, Th/Nb and lower K 2 O/TiO 2 , Zr/Hf, Ba/Rb ratios. From the Sm‐Nd isotopic geochemistry, εNd(0) and 147 Sm/ 144 Nd values of Garze loess and paleosol samples are clearly lower than the NC loess. The higher Bi, Zr and Hf concentrations are relevant to the widely distributed acid‐magmatic rocks in this region, whereas the higher contents of Li, Cs, Rb are attributed to the high background values of the TP. The geochemical characteristics of the Garze loess and paleosol samples further prove that the local glacial and other Quaternary detrital sediments are predominantly the contributors for the eolian deposits on the eastern margin of the TP. Stable element concentrations and their ratios in the Garze loess and paleosol samples formed at different times have relatively greater variation ranges in comparison with the NC loess, indicating that the source regions for eolian deposits have been unstable since the late Early Pleistocene. We attribute the instability of dust sources to variable earth surface conditions and the changeable TP winter monsoon in direction and intensity, which are in turn related to the uplift of the TP.