Weathered and unweathered surface spectra of rocks from cold deserts: Identification of weathering processes and remote sensing implications

Abstract

Abstract Comparisons of the reflectance spectra of weathered and unweathered surfaces of rocks from the Canadian Shield reveal that significant spectral changes can be effected by even the low weathering rates prevalent in cold desert regions. These changes include variations in overall spectral slope, the appearance/disappearance of absorption bands, shifts in absorption band minima wavelength positions, and changes in band shape. The most important alteration processes involve the oxidation of ferrous to ferric iron and the formation of hydrated mineral species. Ferric iron absorption bands are most intense for the most iron-rich lithologies. This may have important implications for the remote sensing detection of iron-rich lithologies such as iron formations and ultramafics. Aluminium- and magnesium-rich lithologies give rise to A1-OH and Mg-OH absorption bands in weathered surface spectra. Dramatic spectral variations betwen interior and exterior spectra occur even when weathered surfaces are thin eno...