Near-infrared spectral characterization of the abyssal serpentinites and its implications for Martian exploration

Abstract

Serpentinization processes can produce localized habitable environments and thus serpentinite becomes an important target for Martian exploration. Identification of serpentinite on Mars primarily relies on the detection of characteristics absorption bands in near-infrared spectra, leveraging laboratory data of pure serpentines. However, serpentinites are mixtures of various hydrous minerals produced during serpentinization processes and primary minerals, resulting in complex spectral features. In this study, extensive mineralogical and spectroscopic analyses, including Micro-X-ray fluorescence (μXRF), near-infrared (NIR) spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM), have been conducted on abyssal serpentinite recovered from the Doldrums Transform Fault at the Mid-Atlantic Ridge (7–8°N). The results show that both orthopyroxene and magnetite in serpentinites have strong influences on serpentine identification using NIR spectroscopy. The absorption feature at 2.12 μm disappears diagnostic for serpentine in the samples containing impure serpentine. Our results call in question the reliance on the presence of 2.12 μm absorption band for detection of serpentine on Mars. In contrast, both sharp absorption at 1.39 μm and asymmetric absorption at 2.32 μm are prevalent in serpentines, even when they are mixed with orthopyroxenes. More importantly, the band depth at 1.39 μm increases with the modal abundance of serpentine and display a strong linear correlation with an R² of 0.82. Although the situation on the unknown Martian surface is more complex, our findings provide a valuable reference for detecting serpentinites using hyperspectral remote sensing data for future exploration on Mars.