Major-Element Compositional Diversity Observed by ChemCam Along the MSL Traverse: The First Three Years

Thursday, 17 December 2015
Poster Hall (Moscone South)
Roger C Wiens1, Nicolas Mangold2, Sylvestre Maurice3, Diana L Blaney4, Samuel M Clegg5, Patrick James Gasda5, Jens Frydenvang5, Olivier Gasnault6, Olivier Forni3, Agnes Cousin3, Jeremie Lasue3, Nina Lanza5, Ryan B Anderson7, Violaine Sautter8, John Bridges9, Laetitia Le Deit2, Marion Nachon10, William Rapin6, Pierre-Yves Meslin11, Horton E Newsom12, Benton C Clark13, David T Vaniman14, Nathan Bridges15, Kenneth E Herkenhoff7, Bethany L Ehlmann16, Melinda Darby Dyar17, Martin R Fisk18, Raymond Francis19, Richard J Leveille20, Jeffrey Roy Johnson21, Nouredine Melikechi22, Ryan Jackson23, Cecile Fabre24, Valérie Payré24, John P Grotzinger16, Ashwin R Vasavada4, Joy A Crisp4 and the ChemCam Team, (1)Space Science and Applications, Los Alamos, NM, United States, (2)LPGN Laboratoire de Planétologie et Géodynamique de Nantes, Nantes Cedex 03, France, (3)IRAP, Toulouse, France, (4)Jet Propulsion Laboratory, Pasadena, CA, United States, (5)Los Alamos National Laboratory, Los Alamos, NM, United States, (6)Universite de Toulouse, Toulouse Cedex 4, France, (7)USGS Astrogeology Science Center, Flagstaff, AZ, United States, (8)CNRS, Paris Cedex 16, France, (9)University of Leicester, Leicester, United Kingdom, (10)University of Nantes, Nantes, France, (11)Universite Paul Sabatier, Toulouse, France, (12)University of New Mexico Main Campus, Albuquerque, NM, United States, (13)Space Science Institute Boulder, Boulder, CO, United States, (14)Planetary Science Institute Tucson, Tucson, AZ, United States, (15)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (16)California Institute of Technology, Pasadena, CA, United States, (17)Mount Holyoke College, South Hadley, MA, United States, (18)Oregon State Univ, Corvallis, OR, United States, (19)University of Western Ontario, London, ON, Canada, (20)McGill University, Montreal, QC, Canada, (21)Johns Hopkins University, Baltimore, MD, United States, (22)Delaware State University, Dover, DE, United States, (23)Univ New Mexico, Albuquerque, NM, United States, (24)University of Lorraine Nancy, Nancy Cedex, France
ChemCam on Curiosity has used LIBS to obtain elemental compositions of >6000 target points at distances to 7.4 m from the rover. Observations include igneous clasts, sediments, diagenetic features, and other details often not accessible by the rover arm. A major re-calibration was recently completed using >350 standards. This significantly improved the accuracies of mineral end-members including plag-feldspars, hi-Si compositions, oxide grains, Mg-rich end-members (presumably Mg saponites; not yet confirmed by CheMin), and Mg and Ca sulfates. Here we draw conclusions from the overall compositional distributions observed in Gale crater from landing until the present using the new calibration.

Observations from Bradbury Rise (sols 0-53, 326-520) show a scattering of compositions toward mineral end-members from igneous clasts and pebbles transported from the crater rim. In contrast, Sheepbed mudstones (first drill location; sols 126-300) form a tight cluster close to average Mars composition. The nearby Shaler fluvial sandstone outcrop (sols 306-325)--the first outcrop of potential deltaic foreset beds--shows K enrichment. This enrichment reaches a peak of 6 wt % K2O (sol 625) in the Mt. Remarkable member of the Kimberley formation, Kimberley being a drill location flanked by foreset beds 7 km SW of Shaler. The Pahrump outcrop (sols 753-919)—first observed material of the Murray formation at Mt. Sharp’s base—shows lower Mg, higher Si, and much higher Al, consistent with stronger alteration. Further along the traverse ChemCam discovered an outcrop of light-toned Murray formation rock (sols 992 on) of nearly pure SiO2+TiO2. Overall, the ChemCam database points to a very strong diversity of inputs and alteration processes within a relatively short distance within Gale.

Igneous compositions: while Jake Matijevic, a float analyzed early by APXS, appeared nepheline normative, no clear nepheline has been found by ChemCam. Additionally, despite the significant number of coarse-grained feldspar-rich rocks observed by ChemCam, only a small number of points show excess silica, and quartz has not been clearly observed, leading to the suggestion that the leucocratic igneous clasts are dioritic/trachybasaltic rather than granitic.