¹Mariek E. Schmidt, ^2,3Glynis M. Perrett, ¹Samantha L. Bray, ¹Nicholas J. Bradley, ^1,4Rebekka E. Lee, ⁵Jeff A. Berger, ⁵John L. Campbell, ⁶Cathy Ly, ²Steven W. Squyres, ⁵Dustin Tesselaar
Journal of Geophysical Research, Planets Link to Article [https://doi.org/10.1029/2018JE005553]
¹Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
²Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA
³Wilfrid Laurier University, Department of Physics and Computer Science, Waterloo, Ontario, Canada
⁴Lafarge Aggregates, Mississauga, Canada
⁵Department of Physics, University of Guelph, Guelph, Ontario, Canada
⁶Cornell University, Ithaca, NY, USA
Published by arrangement with John Wiley & Sons

A thin, patchy layer of airfall dust covers rock surfaces examined by the Mars Science Lab (MSL) rover Curiosity and complicates interpretation of textures in Mars Hand Lens Imager (MAHLI) images and compositions determined by Alpha Particle X‐ray Spectrometer (APXS). Using three image processing methods, we estimate dust coverages for MAHLI images of APXS targets to Sol 1512. Dust coverages of ‘as is’ rock targets range from 6 to 77% (±5 to 10% estimated error). Targets brushed by the Dust Removal Tool (DRT) range to lower coverages than ‘as is’ targets, but quality depends on surface type; brushed mudstones have the narrowest range and lowest coverages (11‐25%), while sandstones vary, ranging to higher coverages (12‐58%). Groups of rocks with similar compositions (APXS classes) can have strong correlations between dust coverage and SO3/Cl (up to r=0.985). Dust can also strongly affect the lightest elements measured (Na to Ca). By comparing paired ‘as is’ and DRT analyses, using the determined dust coverages, and finding a best fit dust thickness (generally ~10 μm), we model relative contributions of the dust and bedrock to extrapolate dust‐free compositions for homogeneous APXS classes. The dust is basaltic with high S and Cl. Dust‐free rocks have higher SiO2 and Na2O (up to 6.5 wt% and 0.5 wt% higher, respectively) and lower SO3 and CaO (up to 5.5 wt% and 1.3 wt% lower, respectively) than dusty equivalents. Dust most influences compositions that are very different from average Mars, including the alkali‐rich, MgO‐poor Jake M class.

^1,2Lu Pan, ^1,3Bethany L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005461]
¹Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, CA, USA
²Laboratoire de Geologie de Lyon, Université Claude Bernard Lyon 1Villeurbanne, France
³Jet Propulsion Laboratory, California Institute of TechnologyPasadena, CA, USA
Published by Arrangement with John Wiley & Sons

Amazonian‐aged Lyot crater is the best‐preserved and deepest peak‐ring impact crater (diameter, D=220km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO) to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggests they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn‐depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars’ surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals.

¹Arya Udry,²Esteban Gazel,³Harry Y. McSween Jr
Journal of Geophyisical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005602]
¹Department of Geoscience, University of Nevada, Las Vegas
²Department of Earth and Atmospheric Sciences, Cornell University
³Department of Earth and Planetary Sciences, University of Tennessee
Published by Arrangement with John Wiley & Sons

The recent discovery of some ancient evolved rocks in Gale crater by the Curiosity rover has prompted the hypothesis that continental crust formed in early martian history. Here we present petrological modeling that attempts to explain this lithological diversity by magma fractionation. Using the thermodynamical software MELTS, we model fractional crystallization of different martian starting compositions that might generate felsic igneous compositions like those analyzed at Gale crater using different variables, such as pressure, oxygen fugacities, and water content. We show that similar chemical and mineralogical compositions observed in Gale crater felsic rocks can readily be obtained through different degrees of fractional crystallization of basaltic compositions measured on the martian surface. The results suggest that Gale crater rocks may not represent true primary liquids as they possibly accumulated and/or fractionated feldspar. In terms of major element compositions and mineralogy, we found that the Gale crater felsic compositions are more similar to fractionated magmas produced in Earth’s intraplate volcanoes than to terrestrial felsic continental crust as represented by tonalite‐trondhjemite‐granodiorite (TTG) suites. We conclude that the felsic rocks in Gale crater do not represent continental crust, as it is defined on Earth.