Tracking the weathering of basalts on Mars using lithium isotope fractionation models

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 16; no. 4; pp. 1172 - 1197
• Main Authors: Fairén, Alberto G., Losa-Adams, Elisabeth, Gil-Lozano, Carolina, Gago-Duport, Luis, Uceda, Esther R., Squyres, Steven W., Rodríguez, J. Alexis P., Davila, Alfonso F., McKay, Christopher P.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.04.2015; John Wiley & Sons, Inc; John Wiley and Sons Inc
• Subjects: Atmospheres; Basalt; basalt weathering; Composition; Composition of the Planets; Environmental conditions; Evaporation; Evaporation rate; Fractionation; Freezing; Geochemical Modeling; Geochemistry; Hydrothermal Systems and Weathering on Other Planets; Isotope fractionation; Isotopes; isotopic fractionation; Lithium; Mars; Mineralogy and Petrology; Minerals; Planetary Geochemistry; Planetary Sciences: Astrobiology; Planetary Sciences: Comets and Small Bodies; Planetary Sciences: Fluid Planets; Planetary Sciences: Solar System Objects; Planetary Sciences: Solid Surface Planets; Relative abundance; Stable isotopes; Sublimation; Supersaturation; Volcanology; Weathering; Mars; lithium; isotopic fractionation; basalt weathering
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1002/2015GC005748

Lithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt‐forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium—7Li and 6Li—have a large relative mass difference (∼15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals—the source of Li—and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's history. Key Points: Modeling of Martian aqueous processes leading to Li isotope fractionation Li isotopic data relevant to understand early Mars environmental conditions Evaporation, sublimation, and freezing processes included in the models