Clay coatings on sands in the western Qaidam Basin, Tibetan Plateau, China: Implications for the Martian clay detection

Abstract

The widespread clay minerals on Mars have been detected using orbital data using near-infrared spectroscopy, which is limited by its shallow detection depth, low recognition precision and resolution, and can only be qualitative etc. Terrestrial analogues on the Earth provide valuable guidance to further understand the distribution and occurrence of clay minerals on Mars. In this study, seven detrital samples with clay minerals as coatings (Abbreviated as “clay coatings”) were collected from four sites in the western Qaidam Basin, a Martian analogue terrain. We identify the mineralogy of the surface coatings to be illite and chlorite, as confirmed by a combination techniques of X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Probe X-ray Microanalysis (EPMA) and Near-infrared spectroscopy (NIR). The NIR results suggested that merely small amounts of clay minerals (~0.5 mg/cm2 and about several micrometers in thickness) masking the surface of sands could lead to well-distinguished characteristic NIR absorption, and their band depth could reach those measured from Martian soil analogues with ~5 wt% to 25 wt% clay minerals at 2.20–2.40 μm. The results of the synthesized samples as coating analogues with clay minerals coated on the surface of quartz grains showed a consistent trend as that of the field samples on the Earth. The further mineralogical analysis indicated that the origin of clay minerals in the coatings of Qaidam Basin is of Aeolian source. Environmental similarities between western Qaidam Basin and Martian surface suggested that various rock coatings potentially exist on Mars and they could affect the mineral detection and the accuracy of mineral identification by remote sensing.