¹B. Bultel,²M. Wieczorek,³Anna Mittelholz,^4,5Catherine L. Johnson,⁶Jérôme Gattacceca,^7,8,9Valentin Fortier,¹⁰Benoit Langlais
Journal of Geophyisical Research (Planets) Open Access Link to Article [https://doi.org/10.1029/2023JE008111]
¹GEOPS, Université Paris-Saclay, CNRS, Orsay, France
²Institut de Physique du Globe de Paris, Université Paris Cité, CNRS, Paris, France
³Department of Earth and Planetary Sciences, ETH Zurich, Zurich, Switzerland
⁴University of British Columbia, Vancouver, BC, Canada
⁵Planetary Science Institute, Tucson, AZ, USA
⁶Aix-Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
⁷Université Catholique de Louvain-la-Neuve, Earth and Life Institute, Louvain-la-Neuve, Belgium
⁸Laboratoire G-Time, Université Libre de Bruxelles, Bruxelles, Belgium
⁹Géosciences Montpellier, CNRS, Univ. Montpellier, Montpellier, France
¹⁰ de Planétologie et Géosciences UMR 6112, Nantes Université, Univ Angers, Le Mans Université, CNRS, Nantes, France
Published by arrangement with John Wiley & Sons

Strong magnetic fields have been measured from orbit around Mars over parts of the ancient southern highlands crust and on the surface at the InSight landing site. The geological processes that are responsible for generating strong magnetization within the crust remain poorly understood. One possibility is that intense aqueous alteration of crustal materials, through the process of serpentinization, could have produced magnetite that was magnetized in the presence of a global core-generated magnetic field. Here, we test this idea with geophysical and geochemical models. We first determine the magnetizations required to account for the observed magnetic field strengths and then estimate the amount of magnetite necessary to account for these magnetizations. For the strongest orbital magnetic field strengths, about 7 wt% magnetite is required if the magnetic layer is 10 km thick. For the surface field strength observed at the InSight landing site, 0.4–1.1 wt% magnetite is required if the magnetic layer corresponds to one or more of the three crustal layers observed in the InSight seismic data (with thicknesses from 8 to 39 km). We then investigate the minerals that are produced by aqueous alteration for various possible crustal compositions and water-to-rock ratios using a thermodynamic model. Magnetite abundances up to 6 wt% can be generated for dunitic compositions that could account for the strongest magnetic anomalies. For more representative basaltic starting compositions, however, more than 0.4 wt% can only be generated when using high water-to-rock ratios, which could account for the weaker magnetizations beneath the InSight landing site.