Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?

Beyssac, O. and Clave, Elise and Forni, O. and Udry, A. and Pascuzzo, A.C. and Dehouck, E. and Beck, P. and Mandon, L. and Quantin-Nataf, C. and Mangold, N. and Lopez-Reyes, G. and Royer, C. and Gasnault, O. and Gabriel, T.S.J. and Kah, L. and Schröder, Susanne and Johnson, J.R. and Bertrand, T. and Chide, B. and Fouchet, T. and Simon, J.I. and Montmessin, F. and Fau, A. and Maurice, S. and Wiens, R.C. and Cousin, A. (2026) Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering? Earth and Planetary Science Letters, 675, p. 119746. Elsevier. doi: 10.1016/j.epsl.2025.119746. ISSN 0012-821X.

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Official URL: https://dx.doi.org/10.1016/j.epsl.2025.119746

Abstract

Based on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock.

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