In Situ Carbonation of Sedimentary and Igneous Rocks of Ultramafic Composition in Jezero Crater, Mars

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Abstract
Over 3.5 years of exploration in Jezero Crater, the Perseverance rover has explored several geological units of diverse origins and natures, performing multi‐technique remote analyses of the chemistry and mineralogy of rocks with the SuperCam instrument suite. Three of these units are dominated by mafic to ultramafic rocks: the igneous rocks of Séítah (olivine cumulate on the crater floor), the sedimentary rocks of the Upper Fan (Western delta) and the Margin Unit, of likely igneous origin. Despite their diverse natures, these three different units present similar mineralogical assemblages with: (a) primary igneous minerals (olivine, pyroxene, Cr‐rich Ti‐Fe oxides), (b) Fe‐Mg carbonate, (c) hydrated/hydroxylated silica, and (d) phyllosilicates. The abundance of carbonate is variable, and we estimate it around 3–9 wt.% and up to 6–16 wt.% carbonate mineral in the Upper Fan and Margin Unit, respectively. We propose that most of these carbonates formed through in situ carbonation of mafic/ultramafic material, whether these rocks were emplaced through igneous or sedimentary processes. The distribution of carbonate with elevation in the Upper Fan and Margin Unit suggests a contribution of the lacustrine activity to the carbonate process, possibly enhanced by hydrothermal activity. These in situ observations may be extrapolated to other carbonates‐bearing rocks on Mars and would make the amount of carbon potentially stored in Martian ultramafic rocks overall significant. This would suggest that carbonation of ultramafic rocks might have played a key role in pumping CO 2 from and therefore in cooling the Martian atmosphere.

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