Raman, Mid-IR, and NIR spectroscopic study of calcium sulfates and mapping gypsum abundances in Columbus crater, Mars

Abstract

Calcium sulfates, including gypsum, bassanite, and anhydrite, have been identified on Mars by orbital and in situ remote sensing observations. A comprehensive spectroscopic study of three calcium sulfates in laboratory was performed. Raman, mid-infrared (mid-IR), and near infrared (NIR) spectra of the samples were acquired. The assignments for fundamental modes are made in the Raman and the mid-IR spectra and for overtones and combinational modes in the NIR spectra. Finally, we performed a case study to derive the abundance of gypsum in Columbus crater on Mars using the spectral unmixing analysis method. Our results show high abundance of gypsum and moderate abundance of hydrated sulfate without any basaltic glass or amorphous weathering products, which indicates these deposits could have formed through precipitation and evaporation and is consistent with the deep lake hypothesis proposed by previous studies.