Combined VNIR and Raman spectroscopy of the Atacama salt flats as a potential Mars analog

Abstract:

The identification and characterization of hydrated minerals within ancient aqueous environments on Mars are high priorities for determining the past habitability of the red planet. Few studies, however, have focused on characterizing the entire mineral assemblage, even though it could aide our understanding of past environments. In this study we use both spaceborne (Landsat, Hyperion) and field (VNIR + Raman spectroscopic) analyses to study the mineralogy of various salt flats (salars) of the northern region of Chile as an analog for Martian evaporites.

Core and marginal zones within the salars are easily distinguished on the Landsat 8 band color composites. These areas host different mineralogic assemblages that often result in different landscape types (see Flahaut et al., EPSC 2015). The lower elevation Salar de Atacama, located in the Andean pre-depression, is characterized by a unique thick halite crust at its center, whereas various assemblages of calcium (gypsum, anhydrite) and sodium (mirabilite) sulfates and clays were found at its margin. Sulfates form the main crust of the Andean salars to the east, although various compositions are observed. These compositions seem to be controlled by the type of brine (Ca, SO₄ or mixed). Sulfate crusts were found to be generally thin (<5 cm) with a sharp transition to the underlying clay, silt or sand-rich alluvial deposits.

Used together, VNIR and Raman spectroscopy, plus morphologic analyses provided a powerful tool to distinguish among different types of salt crusts. Ongoing XRD analyses will quantify the mineral assemblages. We found that the Atacama’s unique arid and volcanic environment, coupled with the transition recorded in some of the salars has a strong Mars analogue potential. Characterizing the outcrops at a variety of environments from alkaline, lake waters to more acidic salar brines and the mineralogy observed at these sites may facilitate constraining geochemical environments on Mars.