Abstract
AbstractVera Rubin ridge (VRR) is an erosion‐resistant feature on the northwestern slope of Mount Sharp in Gale crater, Mars, and orbital visible/shortwave infrared measurements indicate it contains red hematite. The Mars Science Laboratory Curiosity rover performed an extensive campaign on VRR to study its mineralogy, geochemistry, and sedimentology to determine the depositional and diagenetic history of the ridge and constrain the processes by which the hematite could have formed. X‐ray diffraction (XRD) data from the CheMin instrument of four samples drilled on and below VRR demonstrate differences in iron, phyllosilicate, and sulfate mineralogy and hematite grain size. Hematite is common across the ridge, and its detection in a gray outcrop suggest localized regions with coarse‐grained hematite, which commonly forms from warm fluids. Broad XRD peaks for hematite in one sample below VRR and the abundance of FeOT in the amorphous component suggest the presence of nanocrystalline hematite and amorphous Fe oxides/oxyhydroxides. Well crystalline akaganeite and jarosite are present in two samples drilled from VRR, indicating at least limited alteration by acid‐saline fluids. Collapsed nontronite is present below VRR, but samples from VRR contain phyllosilicate with d(001) = 9.6 Å, possibly from ferripyrophyllite or an acid‐altered smectite. The most likely cementing agents creating the ridge are hematite and opaline silica. We hypothesize late diagenesis can explain much of the mineralogical variation on the ridge, where multiple fluid episodes with variable pH, salinity, and temperature altered the rocks, causing the precipitation and crystallization of phases that are not otherwise in equilibrium.
Highlights
Gale crater was selected as the landing site for the Mars Science Laboratory (MSL) Curiosity rover because of orbital detections of a variety of minerals and diversity of potentially habitable geologic environments in the ancient layered sedimentary rocks that comprise the lower slopes of Aeolis Mons, informally known as Mount Sharp (Golombek et al, 2012)
Orbital visible/shortwave infrared (VSWIR) reflectance spectra acquired from portions of lower Mount Sharp by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter show distinct units containing minerals that likely formed from aqueous alteration, including hematite (α‐Fe2O3), smectite, and sulfates (Fraeman et al, 2013, 2016; Milliken et al, 2010)
Analyses of Chemistry and Mineralogy (CheMin) data from the samples drilled on and just below Vera Rubin ridge (VRR) show that the samples are composed of igneous minerals, iron oxides and oxyhydroxides, sulfates, phyllosilicates, and X‐ray amorphous materials (Figure 7)
Summary
Gale crater was selected as the landing site for the Mars Science Laboratory (MSL) Curiosity rover because of orbital detections of a variety of minerals and diversity of potentially habitable geologic environments in the ancient layered sedimentary rocks that comprise the lower slopes of Aeolis Mons, informally known as Mount Sharp (Golombek et al, 2012). Orbital visible/shortwave infrared (VSWIR) reflectance spectra acquired from portions of lower Mount Sharp by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter show distinct units containing minerals that likely formed from aqueous alteration, including hematite (α‐Fe2O3), smectite, and sulfates (Fraeman et al, 2013, 2016; Milliken et al, 2010). These sediments were deposited ~3.5 Ga ago and may preserve evidence for a dramatic change in climate early in Mars' history. Mudstone deposits are especially prevalent on the lower slopes of Mount Sharp, and rarity of desiccation features suggests the lakes were long lived (Grotzinger et al, 2015)
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