¹Fox, V.K., ¹Arvidson, R.E., ¹Guinness, E.A., ²Mclennan, S.M., ¹Catalano, J.G., ³Murchie, S.L., ¹Powell, K.E.
Geophysical Research Letters (in Press) Link to Article [DOI: 10.1002/2016GL069108]
¹Department of Earth and Planetary Sciences Washington University in St. Louis St. Louis, Missouri USA
²Department of Geosciences Stony Brook University Stony Brook, New York USA
³Applied Physics Laboratory The Johns Hopkins University Laurel, Maryland USA

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¹Litvak, M.L. et al. (>10)*
Journal of Geophysical Research E: Planets 121,836-845 Link to Article [DOI: 10.1002/2015JE004960]
¹Space Research Institute, RAS, Moscow, Russian Federation
Published by arrangement with John Wiley & Sons
*Find the extensive, full author and affiliation list on the publishers website

The Dynamic Albedo of Neutron (DAN) instrument on board the Mars Science Laboratory Curiosity rover acquired a series of measurements as part of an observational campaign of the Kimberley area in Gale crater. These observations were planned to assess the variability of bulk hydrogen and neutron-absorbing elements, characterized as chlorine-equivalent concentration, in the geologic members of the Kimberley formation and in surface materials exposed throughout the area. During the traverse of the Kimberley area, Curiosity drove primarily over the “Smooth Hummocky” unit, a unit composed primarily of sand and loose rocks, with occasional stops at bedrock of the Kimberley formation. During the Kimberley campaign, DAN detected ranges of water equivalent hydrogen (WEH) and chlorine-equivalent concentrations of 1.5–2.5 wt % and 0.6–2 wt %, respectively. Results show that as the traverse progressed, DAN observed an overall decrease in both WEH and chlorine-equivalent concentration measured over the sand and loose rocks of the Smooth Hummocky unit. DAN measurements of WEH and chlorine-equivalent concentrations in the well-exposed sedimentary bedrock of the Kimberley formation show fluctuations with stratigraphic position. The Kimberley campaign also provided an opportunity to compare measurements from DAN with those from the Sample Analysis at Mars (SAM) and the Alpha-Particle X-ray Spectrometer (APXS) instruments. DAN measurements obtained near the Windjana drill location show a WEH concentration of ~1.5 wt %, consistent with the concentration of low-temperature absorbed water measured by SAM for the Windjana drill sample. A comparison between DAN chlorine-equivalent concentrations measured throughout the Kimberley area and APXS observations of corresponding local surface targets and drill fines shows general agreement between the two instruments.

¹Le Deit, E. et al. (>10)*
Journal of Geophysical Research E: Planets 121, 784-804 Link to Article [DOI: 10.1002/2015JE004987]
¹Laboratoire de Planétologie et Géodynamique, LPG-Nantes, UMR CNRS 6112, Université de Nantes, Nantes, France
Published by arrangement with John Wiley & Sons
*Find the extensive, full author and affiliation list on the publishers website

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.

¹Ma, C., ¹Beckett, J.R.
American Mineralogist 101, 1161-1170 Link to Article [DOI: 10.2138/am-2016-5399]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, United States
Copyright: The Mineralogical Society of America

Majindeite (IMA 2012-079), Mg2Mo3O8, is a new mineral, occurring as submicrometer-sized crystals with Ni-Fe and Ru-Os-Ir alloys, ± apatite and Nb-oxide. The observed assemblages are partially or wholly enclosed by MgAl2O4 spinel in a Type B1 Ca-Al-rich inclusion, ACM-2, from the Allende CV3 carbonaceous chondrite. The type majindeite has an empirical formula of (Mg1.57Fe0.43)Mo3.00O8, and a nolanite-type P63mc structure with a = 5.778 Å, c = 9.904 Å, V = 286.35 Å3, and Z = 2, leading to a calculated density of 5.54 g/cm3. Majindeite likely formed during the subsolidus oxidation of Mo-rich precursor phase(s) included in Fe-Ni rich alloys in a system that was open to O, Mg, and Ca, which were derived externally and introduced via cracks, subgrain boundaries, and/or surfaces exposed at the exterior of the spinel. If magnetite existed in the phase assemblage, it was lost due to Fe volatilization prior to the formation of majindeite. The immediate precursor to majindeite was likely kamiokite. Majindeite formed during an oxidation event contemporaneous with or postdating the formation of grossular-rich veins in melilite. Kamiokite, the Fe-rich analog of majindeite, also occurs in ACM-2 but only within phase assemblages that contain magnetite and which are entirely enclosed in melilite ± alteration products. Here, grossular-rich veins are not observed and the coexisting awaruites are more Fe-rich than those observed with majindeite. As with majindeite, the precursors for kamiokite grains were also likely to have been Mo-rich alloys, but the Mo-oxide remained magnetite-saturated throughout the alteration process and therefore remained Fe-rich. © 2016 by Walter de Gruyter Berlin/Boston 2016.