REE geochemistry of modern eolian dust deposits in Harbin city, Heilongjiang province, China: Implications for provenance

摘要

There has long been disagreement about the provenance of sandy dust deposits in Harbin city, Heilongjiang province, China. The present paper contributes to a better understanding of the source of sandy dust deposits in Harbin by the application of REE geochemistry. The REE composition of samples from sand-dust deposit events in Harbin was compared with that of three different grain size fractions (<11 mu m, 11-30 mu m and 30-63 mu m) of sandy soil samples from Horqin Sandy Land and Songnen Sandy Land. The results indicate that the REE distributions of all of the Harbin sand-dust samples are remarkably similar to each other, with distinct negative Eu anomalies and slightly negative Ce anomalies, indicating a stable provenance. Grain size exerts a significant influence on REE compositions, with a negative Eu-anomaly tending to develop with decreasing grain size. However, Ce is less influenced by grain size. The large lines of evidences, such as REE contents, distribution patterns, characteristic parameters, delta Eu (delta Eu = Eu anomalies values) vs. Sigma REEs diagram, delta Eu vs. (LREE/HREE) diagram and (LREE/HREE) vs. La-N (subscript N represents chondrite normalized values) diagram, indicate that REE composition of dust deposits in Harbin is quite similar to that of samples from Horqin Sandy Land, especially in the case of the 11-30 mu m grain size fraction. This indicates that the Harbin sand-dust deposits are derived from Horqin Sandy Land and not from Songnen Sandy Land, and that material contribution of Horqin Sandy Land to Harbin dust deposits was mainly 11-30 mu m grain-size fraction. The importance of the Horqin Sandy Land as a major source of Harbin sand-dust weather is supported by meteorological records and meteorological data