Nd–Sr isotope geochemistry of fine-grained sands in the basin-type deserts, West China: Implications for the source mechanism and atmospheric transport

Abstract

The basin-type deserts of West China are among the greatest dust emission areas in the world. Mineral dust that is emitted from the deserts is transported and deposited in east-central China and even in far-east regions. This study investigates the Nd–Sr isotopic compositions of fine-grained surface sands (<75μm) from two basin-type deserts of West China (the Taklimakan and Gurbantunggut deserts) to clarify the source areas and atmospheric transport of mineral dust. The Nd isotopes are useful for tracing the provenance and transport of sediments because they depend on the source rocks and are usually used with Sr isotopes which are affected by multiple factors such as chemical weathering, particle sorting and parent rock. The radiogenic isotopic compositions of the dune sands from the Taklimakan Desert range from εNd (0)=−10.9 to −15 and 87Sr/86Sr=0.714 to 0.718, while those of the dune sands from the Gurbantunggut Desert range from εNd (0)=−4.5 to −6 and 87Sr/86Sr=0.711 to 0.713. The isotopic compositions of the fine-grained surface sands are not spatially uniform within each desert and are controlled by the lithological characteristics of the tectonic units in which the deserts are located. The isotopic comparison of the dune sands with other sediments indicates that tectonic denudation and fluvial processes are the main mechanisms of fine particle production of the modern desert sands. In terms of isotope analyses and forward trajectory results, it is further found that the mineral dust is deposited not only in proximal areas, such as the Hexi Corridor, the Chinese Loess Plateau and the Tibet–Qinghai Plateau, but also in distal regions, such as Japan, the Pacific Ocean and Greenland once it is blown out of the Taklimakan Desert. However, the transport and sinks of mineral dust vary with the atmospheric currents.