ChemCam results from the Shaler outcrop in Gale crater, Mars

Ryan Anderson (1) , J.C. Bridges (2) , A. Williams (3) , L. Edgar (4) , A. Ollila (5) , J. Williams (5) , M. Nachon (6) , N. Mangold (6) , M. Fisk (7) , J. Schieber (8) , S. Gupta (9) , G. Dromart (10) , R. Wiens (11) , Stéphane Le Mouélic (6) , O. Forni (12, 13) , N. Lanza (11) , A. Mezzacappa (14) , V. Sautter (15) , D. Blaney (16) , B. Clark (17) , S. Clegg (11) , O. Gasnault (13, 12) , J. Lasue (13, 12) , R. Léveillé (18) , E. Lewin (19) , K.W. Lewis (20) , S. Maurice (13, 12) , H. Newsom (5) , S.P. Schwenzer (21) , D. Vaniman (22)

1 Astrogeology Science Center [Flagstaff]
2 Space Research Centre [Leicester]
3 Department of Earth and Planetary Sciences [Santa Cruz]
4 SESE - ASU School of Earth and Space Exploration
5 EPS - Department of Earth and Planetary Sciences [Albuquerque]
6 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
7 CEOAS - College of Earth, Ocean and Atmospheric Sciences [Corvallis]
8 Department of Geological Sciences [Bloomington]
9 Department of Earth Science and Technology [Imperial College London]
10 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
11 LANL - Los Alamos National Laboratory
12 UT3 - Université Toulouse III - Paul Sabatier
13 IRAP - Institut de recherche en astrophysique et planétologie
14 OSCAR - Optical Science Center for Applied Research
15 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
16 JPL - Jet Propulsion Laboratory
17 SSI - Space Science Institute [Boulder]
18 Department of Natural Resource Sciences
19 ISTerre - Institut des Sciences de la Terre
20 JHU - Johns Hopkins University
21 Dept. of Physical Sciences
22 PSI - Planetary Science Institute [Tucson]

The ChemCam campaign at the fluvial sedimentary outcrop ‘‘Shaler’’ resulted in observations of 28non-soil targets, 26 of which included active laser induced breakdown spectroscopy (LIBS), and all ofwhich included Remote Micro-Imager (RMI) images. The Shaler outcrop can be divided into seven faciesbased on grain size, texture, color, resistance to erosion, and sedimentary structures. The ChemCamobservations cover Facies 3 through 7. For all targets, the majority of the grains were below the limitof the RMI resolution, but many targets had a portion of resolvable grains coarser than 0.5 mm. The Shalerfacies show significant scatter in LIBS spectra and compositions from point to point, but several keycompositional trends are apparent, most notably in the average K2O content of the observed facies. Facies3 is lower in K2O than the other facies and is similar in composition to the ‘‘snake,’’ a clastic dike thatoccurs lower in the Yellowknife Bay stratigraphic section. Facies 7 is enriched in K2O relative to the otherfacies and shows some compositional and textural similarities to float rocks near Yellowknife Bay. Theremaining facies (4, 5, and 6) are similar in composition to the Sheepbed and Gillespie Lake members,although the Shaler facies have slightly elevated K2O and FeOT. Several analysis points within Shaler suggestthe presence of feldspars, though these points have excess FeOT which suggests the presence of Feoxide cement or inclusions. The majority of LIBS analyses have compositions which indicate that theyhttp://dx.doi.org/10.1016/j.icarus.2014.07.0250019-1035/Published by Elsevier Inc.⇑ Corresponding author.E-mail addresses: [e-mail] (R. Anderson), [e-mail] (J.C. Bridges), [e-mail] (A. Williams), [e-mail] (L. Edgar), [e-mail] (A. Ollila), [e-mail] (J. Williams), [e-mail] (M. Nachon), [e-mail] (N. Mangold), [e-mail] (M. Fisk),[e-mail] (J. Schieber), [e-mail] (S. Gupta), [e-mail] (G. Dromart), [e-mail] (R. Wiens), [e-mail] (S. Le Mouélic), [e-mail] (O. Forni), [e-mail] (N. Lanza), [e-mail] (A. Mezzacappa), [e-mail] (V. Sautter), [e-mail] (D. Blaney), [e-mail] (B. Clark), [e-mail] (S. Clegg), [e-mail] (O. Gasnault), [e-mail] (J.Lasue), [e-mail] (R. Léveillé), [e-mail] (E. Lewin), [e-mail] (S. Maurice), [e-mail] (H. Newsom),[e-mail] (D. Vaniman).Icarus 249 (2015) 2–21Contents lists available at ScienceDirectIcarusjournal homepage: www.elsevier.com/ locate/ icarusare mixtures of pyroxene and feldspar. The Shaler feldspathic compositions are more alkaline than typicalfeldspars from shergottites, suggesting an alkaline basaltic source region, particularly for the K2OenrichedFacies 7. Apart from possible iron-oxide cement, there is little evidence for chemical alterationat Shaler, although calcium-sulfate veins comparable to those observed lower in the stratigraphic sectionare present. The differing compositions, and inferred provenances at Shaler, suggest compositionally heterogeneousterrain in the Gale crater rim and surroundings, and intermittent periods of deposition

Mots clés: Mars; surface Mineralogy; Spectroscopy

Domaines: Planète et Univers [physics]

Ryan Anderson, J.C. Bridges, A. Williams, L. Edgar, A. Ollila, et al.. ChemCam results from the Shaler outcrop in Gale crater, Mars. Icarus, 2015, 249, pp.2-21. ⟨10.1016/j.icarus.2014.07.025⟩. ⟨hal-01122787⟩