title: Tracking the weathering of basalts on Mars using lithium isotope fractionation models.
abstract: 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 and6Li-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.
authors.affiliation: Centro de Astrobiología Madrid Spain; Department of Astronomy Cornell University Ithaca New York USA.
authors.forename: Alberto G
authors.initials: AG
authors.lastname: Fairén
authors.affiliation: Departamento de Geociencias Marinas Universidad de Vigo Vigo Spain.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Losa-Adams
authors.affiliation: Departamento de Geociencias Marinas Universidad de Vigo Vigo Spain.
authors.forename: Carolina
authors.initials: C
authors.lastname: Gil-Lozano
authors.affiliation: Departamento de Geociencias Marinas Universidad de Vigo Vigo Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Gago-Duport
authors.affiliation: Departamento de Biología Molecular Universidad Autónoma de Madrid Madrid Spain.
authors.forename: Esther R
authors.initials: ER
authors.lastname: Uceda
authors.affiliation: Department of Astronomy Cornell University Ithaca New York USA.
authors.forename: Steven W
authors.initials: SW
authors.lastname: Squyres
authors.affiliation: Space Science and Astrobiology Division NASA Ames Research Center Mountain View California USA.
authors.forename: J Alexis P
authors.initials: JA
authors.lastname: Rodríguez
authors.affiliation: SETI Institute Mountain View California USA.
authors.forename: Alfonso F
authors.initials: AF
authors.lastname: Davila
authors.affiliation: Space Science and Astrobiology Division NASA Ames Research Center Mountain View California USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: McKay
keywords: Mars; basalt weathering; isotopic fractionation; lithium