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The joint NASA‐ESA Mars sample return campaign aims to return up to 31 sample tubes containing drilled sedimentary and igneous cores and regolith. The titanium alloy tubes will initially still be sealed when they are retrieved. Several types of measurement will be carried out on sealed samples in the pre‐basic characterization phase of scientific investigation. We show that powder x‐ray diffraction (XRD) analysis can be successfully carried out on sealed samples using an x‐ray source at the I12 beamline of Diamond Light Source synchrotron. Our experiment used an analog sample tube and a Martian regolith analog (Icelandic basaltic sand). The titanium walls of the tube analog give strong but few diffraction peaks, making identification of the major constituent mineral phases feasible. A more significant constraint on quantification of mineral phase abundances by this XRD technique is likely to be the grain size of the sample. This technique opens up the possibility of initial mineralogical analysis of samples returned from Jezero crater without opening the sample tubes and the potential changes to the sample that entails. [ABSTRACT FROM AUTHOR]

Data returned by NASA's Mars Science Laboratory Curiosity rover showed evidence for abundant secondary materials, including Fe‐oxides, phyllosilicates, and an amorphous component on and below Vera Rubin ridge in the Murray formation. We used equilibrium thermochemical modeling to test the hypothesis that altered sediments were deposited as detrital igneous grains and subsequently underwent diagenesis. Chemical compositions of the Murray formations' altered components were calculated using data returned by the chemistry and mineralogy X‐ray diffraction instrument and the alpha particle X‐ray spectrometer on board Curiosity. Reaction of these alteration compositions with a CO2‐poor and oxidizing dilute aqueous solution was modeled at 25–100 °C, with 10–50% Fe3+/Fetot of the host rock. The modeled alteration assemblages included abundant phyllosilicates and Fe‐oxides at water‐to‐rock ratios >100. Modeled alteration abundances were directly comparable to observed abundances of hematite and clay minerals at a water‐to‐rock ratio of 10,000, for system temperatures of 50–100 °C with fluid pH ranging from 7.9 to 9.3. Modeling results suggest that the hematite–clay mineral assemblage is primarily the result of enhanced groundwater flow compared to the Sheepbed mudstone observed at Yellowknife Bay, and underwent further, localized alteration to produce the mineralogy observed by Curiosity. [ABSTRACT FROM AUTHOR]

Understanding of the geologic evolution of Mars has been greatly improved by recent orbital, in situ and meteorite data, but insights into the earliest period of Martian magmatism (4.1 to 3.7 billion years ago) remain scarce. The landing site of NASA's Curiosity rover, Gale crater, which formed 3.61 billion years ago within older terrain, provides a window into this earliest igneous history. Along its traverse, Curiosity has discovered light-toned rocks that contrast with basaltic samples found in younger regions. Here we present geochemical data and images of 22 specimens analysed by Curiosity that demonstrate that these light-toned materials are feldspar-rich magmatic rocks. The rocks belong to two distinct geochemical types: alkaline compositions containing up to 67 wt% SiO2 and 14 wt% total alkalis (Na2O + K2O) with fine-grained to porphyritic textures on the one hand, and coarser-grained textures consistent with quartz diorite and granodiorite on the other hand. Our analysis reveals unexpected magmatic diversity and the widespread presence of silica- and feldspar-rich materials in the vicinity of the landing site at Gale crater. Combined with the identification of feldspar-rich rocks elsewhere and the low average density of the crust in the Martian southern hemisphere, we conclude that silica-rich magmatic rocks may constitute a significant fraction of ancient Martian crust and may be analogous to the earliest continental crust on Earth. [ABSTRACT FROM AUTHOR]

Introduction: The nakhlite secondary alteration assemblage consists mainly of Fe-rich carbonate partially corroded and replaced by ferric saponite and an odinite-like serpentine phase [1,2]. This mineral assemblage and its alteration stages can illustrate key aspects of the Amazonian carbon cycle. For instance, the origin of methane in the Martian atmosphere is one of the key unresolved questions in Mars' atmospheric evolution and current near-surface processes [3,4]. A possible route for methane production was described in [5] which demonstrated that CH4 is expected to dominate over carbon oxides under the redox conditions associated with martian hydrothermal fluids and the nakhlite secondary minerals. Here we use mineralogical studies of the Amazonian [6] nakhlite secondary assemblage to explore links between the carbonate-bearing crust and routes for organic formation. Methods and Samples: Mineralogical data on the nakhlite secondary minerals have been gathered with FE-SEM, EDX, WDS, FIB-(S)TEM at University of Leicester's Advanced Microscopy Facility and University of Nottingham, and Fe-K XANES at Diamond Light Source e.g. [1,2]. The 12 nakhlites carry varying abundances and parts of the overall secondary assemblage depending on depth of the parent rock within the nakhlite pile and extent of exposure to the secondary fluid [1,2,7]. We have studied many of the nakhlites as part of this project, but the near pristine nakhlite Lafayette has particular importance due to the abundance of its secondary assemblage and the textural evidence for an evolving fluid. We have anlysed Lafayette sections USNM 7849 and a section originally from the CFM. Results: Carbonate is up to 4% of one Lafayette thin section, and Mg0.0-2.0Cc13.2-38.6Sd17.7-81.9Rh3.1-42.9 [1]. A key feature of the nakhlite phylloslicate-carbonate assemblage in the nakhlites is that carbonate is variably replaced by ferric saponite in olivine fractures and odinite-like serpentine in mesostasis textural sites (Fig. 1). For instance, another thin section of the same Lafayette meteorite contained only minute traces of unaltered carbonate, most having been replaced. The odinite-like phase has d001-spacings of 0.7 nm and (Fetot+Mg)/Al at. of 0.8-0.9 [1]. Fe-K XANES show Fe3+/SFe ratios from 0.86-1.0 within the odinite and 0.59-0.96 within the saponite. Small traces of ferrihydrite were identified near the margins of corroded carbonate and saponite. Discussion: The nakhlite secondary fluid was initially a HCO3-charged brine associated with the precipitation of carbonate within olivine and mesostasis sites. Once the fluid's HCO3 was exhausted, the evolving, neutral-mildly alkaline, =50 oC brine corroded the carbonate and precipitated the phyllosilicate as a replacement of carbonate and directly within fractures. As the fluid was no longer buffered by Fe2+-carbonate, the iron oxidation state increased, as recorded in the Fe3+-rich phyllosilicates and precipitation of small traces of ferrihydrite near the margins of corroded carbonate and saponite. Extensive dissolution of such carbonate across the upper martian crust, producing bicarbonate and carbon dioxide, and the coupled formation of ferric phyllosilicates, would lead to the formation of CH4 in substantial amounts via a Fischer-Tropsch type reaction [8-10]. Such reactions could be substantially inhibited by kinetic factors but the likely relatively high abundance of carbonate and clay-bearing assemblages in much of the Mars upper crust [11] suggest that substantial quantities of CH4 and PAHs would still have been created. Seasonal release of some trapped CH4 reservoirs formed from this process are, for instance, of sufficient likely magnitude to explain localised atmospheric CH4 enrichments detected by Mars Science Laboratory [3]. As more of the crust is being studied via meteorites, MSL [12,13], Mars2020-MSR and orbiters, the role and significance of carbonate-phyllosilicate abundances within the ancient carbon cycle and organic reservoirs of Mars will continue to be revealed [14]. [ABSTRACT FROM AUTHOR]

- Secondary mineral assemblages in the nakhlite meteorites, Lafayette, Governador Valadares (GV), Nakhla, Yamato (Y)-000593/Y-000749 have been studied using scanning electron microscopy, transmission electron microscopy, and electron probe micro analysis. The different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases, showing compositional fractionation correlated with their relative depths below the Martian surface. Fracture-filled veins in Lafayette at the bottom of the pile consist of a siderite-phyllosilicate-Fe oxide-hydrated silicate gel assemblage. Corresponding veins in Nakhla and GV further up the pile are predominantly a siderite-gel assemblage, with additional evaporites including gypsum. Y-000593/Y-000749 veins are dominated by gel. The gel's Mg/(Mg + Fe) ratio decreases from Lafayette (0.37) to GV (0.32), Nakhla (0.24), and Y-000593 (0.15). We suggest that hydrothermal fluid flowed up this depth profile, initiated by melting of buried H2O-CO2 ice. Our results show a complex mix of Fe-rich phyllosilicate within the veins and mesostasis of Lafayette with d-spacings of 0.7-1.1 nm suggesting a mixture of smectite and serpentine. The phyllosilicate formed at close to neutral pH, ≤150 °C. We also suggest that water rock ratios (W/R) of 1-10 occurred in Lafayette with smaller values for the other nakhlites. This is reflected in the volume of alteration minerals: 10% of olivine in Lafayette to 3% in Nakhla. Textural evidence of rapid cooling, together with the W/R and likely fluid velocities, suggest that the secondary assemblages formed quickly, e.g., within months. A model is proposed in which the secondary assemblages formed in an impact-induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts. [ABSTRACT FROM AUTHOR]