¹L.M.Thompson et al. (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006319]
¹Planetary and Space Science Centre, University of New Brunswick, Canada
Published by arrangement with John Wiley & Sons

The resistant ~50 m thick Vera Rubin ridge (VRR) situated near the base of Mount Sharp, Gale crater, Mars has been deemed a high priority science target for the Mars Science Laboratory mission. This is because of 1) its position at the base of the 5 km layered strata of Mount Sharp, and 2) the detection of hematite from orbit, indicating that it could be the site of enhanced oxidation. The compositional data acquired by the Alpha Particle X‐ray spectrometer (APXS) during Curiosity’s exploration of VRR helps to elucidate questions pertaining to the formation of the ridge. APXS analyses indicate that VRR falls within the compositional range of underlying lacustrine mudstones, consistent with a continuation of that depositional environment and derivation from a similar provenance. Lower Fe concentrations for VRR compared to the underlying strata discounts the addition of large amounts of hematite to the strata, either as cement or as detrital input. Compositional trends associated with VRR cross‐cut stratigraphy, indicating post‐depositional processes. Higher Si and Al, and lower Ti, Fe and Mn than the underlying mudstone, particularly within distinct patches of gray/blue bedrock are consistent with the addition of Si and Al. Lateral and vertical compositional variations, suggest enhanced element mobility and fluid flow (possibly via multiple events) through VRR, increasing towards the top of the ridge, consistent with the action of warm (~50‐100 °C), locally acidic saline fluids as inferred from the mineralogy of drilled samples.

¹S.R.Jacob et al., (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006290]
¹Arizona State University
Published by arrangement with John Wiley & Sons

During 2018 and 2019, the Mars Science Laboratory Curiosity rover investigated the chemistry, morphology, and stratigraphy of Vera Rubin ridge (VRR). Using orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars, scientists attributed the strong 860 nm signal associated with VRR to the presence of red crystalline hematite. However, Mastcam multispectral data and CheMin X‐ray diffraction (XRD) measurements show that the depth of the 860 nm absorption is negatively correlated with the abundance of red crystalline hematite, suggesting other mineralogical or physical parameters are also controlling the 860 nm absorption. Here, we examine Mastcam and ChemCam passive reflectance spectra from VRR and other locations to link the depth, position, and presence or absence of iron‐related mineralogic absorption features to the XRD‐derived rock mineralogy. Correlating CheMin mineralogy to spectral parameters showed that the ~860 nm absorption has a strong positive correlation with the abundance of ferric phyllosilicates. New laboratory reflectance measurements of powdered mineral mixtures can reproduce trends found in Gale crater. We hypothesize that variations in the 860 nm absorption feature in Mastcam and ChemCam observations of VRR materials is a result of three factors: (1) variations in ferric phyllosilicate abundance due to its ~800‐1000 nm absorption; (2) variations in clinopyroxene abundance because of its band maximum at ~860 nm; and (3) the presence of red crystalline hematite because of its absorption centered at 860 nm. We also show that relatively small changes in Ca‐sulfate abundance is one potential cause of the erosional resistance and geomorphic expression of VRR.

¹J.L’Haridon et al. (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006299]
¹Laboratoire de Planétologie et Géodynamique, UMR6112, CNRS, Univ Nantes, Univ Angers, Nantes, France
Published by arrangement with John Wiley & Sons

The Curiosity rover investigated a topographic structure known as Vera Rubin ridge, associated with a hematite signature in orbital spectra. There, Curiosity encountered mudstones interpreted as lacustrine deposits, conformably overlying the 300 m‐thick underlying sedimentary rocks of the Murray formation at the base of Mount Sharp. While the presence of hematite (α‐Fe2O3) was confirmed in‐situ by both Mastcam and ChemCam spectral observations and by the CheMin instrument, neither ChemCam nor APXS observed any significant increase in FeOT (total iron oxide) abundances compared to the rest of the Murray formation. Instead, Curiosity discovered dark‐toned diagenetic features displaying anomalously high FeOT abundances, commonly observed in association with light‐toned Ca‐sulfate veins but also as crystal pseudomorphs in the host rock. These iron‐rich diagenetic features are predominantly observed in “grey” outcrops on the upper part of the ridge, which lack the telltale ferric signature of other Vera Rubin ridge outcrops. Their composition is consistent with anhydrous Fe‐oxide, as the enrichment in iron is not associated with enrichment in any other elements, nor with detections of volatiles. The lack of ferric absorption features in the ChemCam reflectance spectra and the hexagonal crystalline structure associated with dark‐toned crystals points toward coarse “grey” hematite. In addition, the host rock adjacent to these features appears bleached and show low‐FeOT content as well as depletion in Mn, indicating mobilization of these redox‐sensitive elements during diagenesis. Thus, groundwater fluid circulations could account for the remobilization of iron and recrystallization as crystalline hematite during diagenesis on Vera Rubin ridge.