Inferring alteration conditions on Mars: Insights from near-infrared spectra of terrestrial basalts altered in cold and hot arid environments

Can information on the Martian environmental conditions prevailing during the alteration of its basaltic crust be inferred from near-infrared (NIR) spectra? In order to determine whether basalts altered under arid conditions but different temperatures have different spectral signatures, NIR spectra of basalts altered in cold (Udokan volcanic field, Siberia) and hot (Ogaden Basin, Ethiopia) environments were obtained. The NIR spectra of the alteration rind surface and the internal part of the studied samples are similar, suggesting that the NIR spectra of Martian bulk rocks may be of limited help in identifying paleoenvironment conditions. Bulk rock spectra analysis reveals, however, that spectra of the least altered rocks display clear absorption bands of smectites, suggesting that a distinction between clay minerals in weakly weathered basalts and clay-rich formations cannot be based solely on analysis of infrared spectra obtained from orbit. Additional compositional information can be retrieved from rock powder spectra - zeolites present in the Udokan basalt spectra might be used to infer composition and temperature of the fluids from which they precipitated. The presence of calcite and iddingsite is ascertained by other methods, but they are not apparent in bulk rock spectra and only weakly apparent in powder spectra. The basalt samples studied display alteration products that reflect their different alteration histories; nevertheless no criterion has been found that would help in identifying the origin of the weathering water - subsurface, rainfall, or snowfall.