Sr and Nd isotope ratios and REE abundances of moraines in the mountain areas surrounding the Taklimakan Desert, NW China

摘要

The first systematic data of Sr and Nd isotopic ratios, REE abundances, major element and mineral compositions are reported for the Chinese moraines from the western Kunlun Mts. and southern and northern flanks of the Tianshan Mts. and soils from the Tibet Plateau. This study was conducted in order to characterize the isotopic and geochemical features of these moraines and soils, which are considered as possible sources of the Taklimakan Desert sands. The moraines and the desert sands consist of quartz and feldspar as dominant minerals, but the former have higher clay and mica and lower carbonate mineral abundances than the latter. In spite of the wide variation, average values of most major elements of the moraines are generally similar to those of the Taklimakan Desert sands, except for CaO depletion and K2O enrichment in the motaines. Sr and Nd isotopic ratios are also highly variable for moraines, particularly from the Tianshan northern flank, while those for the desert sands show restricted values. In the Sr-Nd isotopic diagram, the Taklimakan Desert sands are plotted in the narrow field overlapped by both the moraine matrices from the western Kunlun Mts. and from the Tianshan southern flank. In addition, it is noted that average value of Nd isotopic ratios for the moraines is clearly higher than those for the desert sands. Two Tibetan soils of this study show wide variation in mineral composition and major element compositions (SiO2 = 75% and CaO = 1.5% for one sample and SiO2 = 44% and CaO = 31.8% for the other). However, Sr isotopic ratios of both soils are similar to those of the desert sands and their Nd isotopic data are slightly smaller than the desert sands. These results suggest moraine matrices from both the western Kunlun Mts. and the Tianshan southern flank and the Tibetan soils as possible sources for the Taklimakan Desert sands. [References: 30]