REE geochemistry of loess in Xinjiang, China

Abstract

The total rare-earth element values (ΣREE) of loess in the Xinjiang region vary over a range of 128–200 ppm, with an average of 153 ppm. The average REE content of loess lies between the earth’s crust (155 ppm) and sedimentary rocks (151 ppm). The Xinjiang loess, with the REE distribution patterns characterized by negative slopes, is rich in the Ce-family elements, and has a distribution pattern characteristic of sedimentary rocks. The North Xinjiang loess is relatively depleted in Tb, but rich in Yb and Lu. The South Xinjiang loess is relatively rich in light rare-earth elements. This is full proof that the Xinjiang loess comes partly from weathered materials (clay rock, sandstone) in the region studied. The REE distribution patterns in the Xinjiang loess are similar to those in the precipitated dust and aeolian sand, indicating the same material source. The REE distribution patterns in the Xinjiang loess are also similar to those in loess from the middle Yellow River Valley, China and Taskent, the former USSR. This implies that loesses of the three locations (Xinjiang, the middle Yellow River Valley and Taskent) come from a common material source. But the REE patterns in the Xinjiang loess are different from those in wall rocks (volcanic rock, K-bearing volcanic rock). Generally, LREE/HREE, Eu/Eu* and Ce/Ce* ratios reflect the features of parent materials of loess, indicating that the parent rocks were probably in the early stage of alkaline weathering and the weathered materials existed in an oxidation environment with basic mediums under arid-climatic conditions before transport. As a result, the migration ability of the REE is weak.