Variable Iron Mineralogy and Redox Conditions Recorded in Ancient Rocks Measured by In Situ Visible/Near‐Infrared Spectroscopy at Jezero Crater, Mars
Résumé
Using relative reflectance measurements from the Mastcam-Z and SuperCam instruments on the Mars 2020 Perseverance rover, we assess the variability of Fe mineralogy in Noachian/Hesperian-aged rocks at Jezero crater. The results reveal diverse Fe$^{3+}$ and Fe$^{2+}$ minerals. The igneous crater floor, where small amounts of Fe$^{3+}$-phyllosilicates and poorly crystalline Fe$^{3+}$-oxyhydroxides have been reported, is spectrally similar to most oxidized basalts observed at Gusev crater. At the base of the western Jezero sedimentary fan, new spectral type points to an Fe-bearing mineral assemblage likely dominated by Fe$^{2+}$. By contrast, most strata exposed at the fan front show signatures of Fe$^{3+}$-oxides (mostly fine-grained crystalline hematite), Fe$^{3+}$-sulfates (potentially copiapites), strong signatures of hydration, and among the strongest signatures of red hematite observed in situ, consistent with materials having experienced vigorous water-rock interactions and/or higher degrees of diagenesis under oxidizing conditions. The fan top strata show hydration but little to no signs of Fe oxidation likely implying that some periods of fan construction occurred either during a reduced atmosphere era or during short-lived aqueous activity of liquid water in contact with an oxidized atmosphere. We also report the discovery of alternating cm-scale bands of red and gray layers correlated with hydration and oxide variability, which has not yet been observed elsewhere on Mars. This could result from syn-depositional fluid chemistry variations, possibly as seasonal processes, or diagenetic overprint of oxidized fluids percolating through strata having variable permeability
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