Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars

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Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars

E Rampe, D Ming, D Blake, T Bristow, S Chipera, J Grotzinger, R Morris, S Morrison, D Vaniman, A Yen, et al.

To cite this version:

E Rampe, D Ming, D Blake, T Bristow, S Chipera, et al.. Mineralogy of an ancient lacustrine

mudstone succession from the Murray formation, Gale crater, Mars. Earth and Planetary Science

Letters, Elsevier, 2017, 471, pp.172 - 185. �10.1016/j.epsl.2017.04.021�. �insu-03211833�

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Contents lists available atScienceDirect

Earth and Planetary Science Letters

www.elsevier.com/locate/epsl

Mineralogy of an ancient lacustrine mudstone succession from the Murray formation, Gale crater, Mars

E.B. Rampeâ^,^∗, D.W. Mingâ,D.F. Blake^b,T.F. Bristow^b,S.J. Chipera^c,J.P. Grotzinger^d, R.V. Morrisâ,S.M. Morrisonê^,^f,D.T. Vaniman^g, A.S. Yen^h, C.N. Achillesê,P.I. Craigⁱ, D.J. Des Marais^b,R.T. Downsê,J.D. Farmer^j,K.V. Fendrichê, R. Gellert^k,R.M. Hazen^f, L.C. Kah^l,J.M. Morookian^h,T.S. Peretyazhko^m,P. Sarrazinⁿ, A.H. Treiman^h,J.A. Bergerô, J. Eigenbrode^p,A.G. Fairén^q^,^r, O. Forni^s,S. Gupta^t, J.A. Hurowitzû,

N.L. Lanza^v, M.E. Schmidt^w,K. Siebach^d, B. Sutter^m,L.M. Thompson^x

aAstromaterialsResearchandExplorationScienceDivision,NASAJohnsonSpaceCenter,Houston,TX77058,USA bNASAAmesResearchCenter,MoffettField,CA94035,USA

cChesapeakeEnergy,OklahomaCity,OK73154,USA

dDivisionofGeologicandPlanetarySciences,CaliforniaInstituteofTechnology,Pasadena,CA91125,USA eDepartmentofGeosciences,UniversityofArizona,Tucson,AZ85721,USA

fGeophysicalLaboratory,CarnegieInstitutionofWashington,BroadBranchRdNW,Washington,DC20015,USA gPlanetaryScienceInstitute,Tucson,AZ85719,USA

hJetPropulsionLaboratory,CaliforniaInstituteofTechnology,Pasadena,CA91109,USA iLunarandPlanetaryInstitute,Houston,TX77058,USA

jSchoolofEarthandSpaceExploration,ArizonaStateUniversity,Tempe,AZ85287,USA kDepartmentofPhysics,UniversityofGuelph,Guelph,ONN1G2W1,Canada

lDepartmentofEarthandPlanetaryScience,UniversityofTennessee,Knoxville,TN37996,USA mJacobs–JETSContract,Houston,TX77058,USA

nSETIInstitute,MountainView,CA94043,USA

oDepartmentofEarthSciences,UniversityofWesternOntario,London,ONN6A5B7,Canada pNASAGoddardSpaceFlightCenter,Greenbelt,MD20771,USA

qCentrodeAstrobiología,CSIC-INTA,28850Madrid,Spain rDepartmentofAstronomy,CornellUniversity,Ithaca,NY14853,USA

sInstitutdeRechercheenAstrophysiqueetPlanétologie,CNRS,UMR5277,Toulouse,France tDepartmentofEarthSciencesandEngineering,ImperialCollegeLondon,LondonSW72AZ,UK uDepartmentofGeosciences,StonyBrookUniversity,StonyBrook,NY11794,USA

vLosAlamosNationalLaboratory,LosAlamos,NM87545,USA

wDepartmentofEarthSciences,BrockUniversity,St.Catharines,ONL253A1,Canada

xPlanetaryandSpaceScienceCentre,UniversityofNewBrunswick,Fredericton,NBE3B5A3,Canada

a r t i c l e i n f o a b s t ra c t

Articlehistory:

Received3August2016

Receivedinrevisedform3April2017 Accepted12April2017

Availableonline12May2017 Editor:C.Sotin

Keywords:

Mars Galecrater X-raydiffraction diagenesis

acid-sulfatealteration

The Mars Science Laboratory Curiosity rover has been traversing strata at the base of Aeolis Mons (informallyknownasMountSharp)sinceSeptember2014.TheMurrayformationmakesupthelowest exposed strata of the Mount Sharp group and is composed primarily of finely laminated lacustrine mudstoneintercalatedwithrarecrossbeddedsandstonethatisprodeltaicorfluvialinorigin.Wereport onthefirstthree drilledsamples fromtheMurray formation,measuredinthePahrumpHills section.

RietveldrefinementsandFULLPATfullpatternfittinganalysesofX-raydiffractionpatternsmeasuredby theMSLCheMininstrumentprovidemineralabundances,refinedunit-cellparametersformajorphases giving crystalchemistry,andabundancesofX-rayamorphous materials.Ourresultsfromthesamples measured atthe Pahrump Hills and previouslypublished results on the Buckskin sample measured from the Marias Pass section stratigraphically above Pahrump Hills show stratigraphic variations in the mineralogy;phyllosilicates,hematite,jarosite, andpyroxeneare mostabundantatthebase ofthe Pahrump Hills, and crystalline and amorphous silica and magnetite become prevalent higher in the succession. SometraceelementabundancesmeasuredbyAPXSalsoshow stratigraphictrends; Znand Ni are highly enrichedwith respect toaverage Mars crustatthe base ofthe Pahrump Hills (by 7.7 and 3.7 times, respectively),and gradually decrease in abundance in stratigraphicallyhigher regions

* Correspondingauthor.

E-mailaddress:elizabeth.b.rampe@nasa.gov(E.B. Rampe).

http://dx.doi.org/10.1016/j.epsl.2017.04.021

0012-821X/PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

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nearMariasPass,wheretheyaredepleted withrespecttoaverageMarscrust(bymorethananorder of magnitudein some targets). The Mn stratigraphictrend is analogous to Znand Ni,however, Mn abundancesare close tothoseofaverage Marscrustatthebase ofPahrump Hills,rather thanbeing enriched,andMnbecomesincreasinglydepletedmovingupsection.MineralsatthebaseofthePahrump Hills,inparticularjarositeandhematite,aswellasenrichmentsinZn,Ni,andMn,areproductsofacid- sulfate alterationonEarth.We hypothesizethatmultiple influxesofmildlytomoderately acidicpore fluidsresultedindiagenesisoftheMurray formationand theobservedmineralogicalandgeochemical variations.ThepreservationofsomemineralsthatarehighlysusceptibletodissolutionatlowpH(e.g., mafic minerals and fluorapatite)suggests that acidicevents were not long-lived and that fluidsmay not have been extremely acidic (pH>2). Alternatively, the observed mineralogical variations within the succession may be explained by deposition in lake waters with variable Eh and/or pH, where the lowermost sediments weredeposited inan oxidizing, perhapsacidic lake setting,and sediments depositedintheupperPahrumpHills andMariasPassweredepositedlakewaters withlowerEhand higherpH.

PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

The Mars Science Laboratory (MSL) Curiosity rover landed on the plains of Gale crater (Aeolis Palus) to the north of Aeolis Mons(informallyknown as MountSharp) in August 2012to in- vestigate a site presumed to have a variety of ancient aqueous environments and to assess the habitability of these environments (Grotzinger etal., 2012). Visible/short-wave infrared spec- tra from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter show stratigraphic trends in mineralogy in the lower sedimentary layers of Mount Sharp; the lowermost layers contain phyllosilicate, sulfate, and/or iron oxide minerals,withspectral evidence forphyl- losilicate minerals decreasing up section (Milliken et al., 2010;

Fraemanetal., 2013).Stratigraphicchangesinmineralogy suggest thattherocksinlowerMountSharprecordanenvironmentaltran- sitionfromone inwhichphyllosilicatemineralsformed toonein whichsulfatemineralsformed(Millikenetal., 2010).Bystudying the mineralogy and geochemistry of thissedimentary succession insituwithCuriosity,wecanidentifychangesinenvironmentand sedimentsourcesonamuchﬁnerscale.

Bedrock exposed onthe plains northofMount Sharpbelongs tostrataoftheBradburygroupandincludesmudstone,sandstone, andconglomerate sequences deposited in ﬂuvial-lacustrine environments (Grotzinger et al., 2014, 2015; Vasavada et al., 2014).

Themudstone analyzedatYellowknife Baywas interpreted asan ancienthabitable lacustrine environmentbased onits mineralogical and geochemical composition (e.g., Grotzinger et al., 2014;

McLennan etal., 2014; Ming etal., 2014; Vaniman et al., 2014), wherecircumneutral fluidswithlow ionicstrength appear to be associatedwiththein-situdissolutionofolivine andprecipitation offerrian saponiteandmagnetite (Bristow etal., 2015). Curiosity reachedthebaseof MountSharpin September 2014ina region called the Pahrump Hills. Rocks of the Pahrump Hills make up thelowermostportionoftheMurrayformationandaredominated byfinelyhorizontallylaminatedmudstonewithminorintercalated cross-beddedsandstone, suggestingdeposition from lacustrine to fluvial-deltaicenvironments (Grotzingeretal., 2015). The Murray formationis mapped astime-equivalentto coarser-grained strata oftheBradburygroup, withfluvial-deltaicfacies passinglaterally intoandinterfingeringwithlacustrinefacies.

The Murrayformation was studied in detailat Pahrump Hills and at Marias Pass, 6 m stratigraphically above the top of the exposedsectionstudiedatthePahrumpHills(Fig. 1).Detailedin- vestigationsintheselocationsincluded imagingby Mastcamand theMarsHand Lens Imager (MAHLI),geochemical measurements by the Alpha Particle X-ray Spectrometer (APXS) andthe Chem- istryandCamera(ChemCam),anddeliveryofdrilledrockpowders totheinstrumentsinsidethebodyoftherover,theChemistryand

Mineralogy(CheMin) andSample Analysis at Mars(SAM) instru- ments.MineralogicalresultsfromCheMinfortheMariasPassdrill samplearereportedbyMorrisetal.(2016).Here,wereportmin- eralogical resultsfromCheMinof thesamplescollected fromthe PahrumpHillssection,includingmineralabundances,reﬁnedunit- cell parameters, and derived crystal chemistry. We subsequently consider hypotheses about the depositional and diagenetic envi- ronmentsrecordedintheserocks.Basedonmineralogy,geochemistry, and diagenetic features, we propose a model of multiple acidic diagenetic ﬂuid episodes. We also consider deposition in acidsalinelakesasanexplanationfortheobservedmineralogy.

2. Materialsandmethods 2.1. Samples

FourdrillsampleswereacquiredfromthelowerMurrayforma- tionbytheMSLCuriosity’ssampleacquisitionandhandlingsystem and delivered to CheMin for analysis (Figs. 1 and 2). Details of sample acquisitionandprocessingbytheCollection andHandling for In-situ Mars Rock Analysis (CHIMRA, Anderson et al., 2012) andanalysisby theCheMininstrumentarepresentedinthesup- plementarymaterial.Theﬁrstthreesamplesweretakenfromthe Pahrump Hills section of the Murray formation. The Conﬁdence Hills(CH) andMojave 2(MJ)drillsampleswereacquiredonsols 759 and882,respectively, andlie near the baseof thePahrump Hills,withtheMJsamplelocated1.2mstratigraphicallyabovethe CH drill site. The base of the Pahrump Hills records numerous features consistent with multiple diagenetic episodes, including centimeter-scale crystal clusters and dendrites enriched in Mg, Ni,andS,accordingtoAPXSmeasurements(Gellertetal., 2015a;

Kahetal.,2015a; VanBommeletal.,2016);millimeter-scalelentic- ularcrystalpseudomorphs(Kahetal., 2015b);andfracturescon- taining one or two generations of mineral fill (including a late- diageneticcalcium-sulfatephase,Kahetal.,2015a,2015b;Nachon etal.,2017).TheTelegraphPeak(TP)sample wasacquiredonsol 908atanelevation7mabovetheCHsample.TelegraphPeaklies just below a cross-stratified sandstone called Whale Rock, interpreted asatongue ofprodeltaic gulley orlowstand fluvial materials(Grotzingeretal.,2015).TheBuckskin(BK)outcrop(sampled on sol1060)is a ∼^{2–3 m} ^thick ^section ôf^the ^Murray^formation exposedintheMariasPassregion,13mupsectionfromCH(Mor- ris,2016).

2.2. Methods

AllXRDdatawereﬁrstevaluatedbycomparisonsandsearches of the International Center for Diffraction Data (ICDD) Powder

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Fig. 1.A.Curiosity’straversefromlandingthroughSol1185,showinglocationsofPahrumpHillsandMariasPass.Imagecredit:NASA/JPL-Caltech/Univ.ofArizona.Map fromhttp://mars.jpl.nasa.gov/msl/news/whatsnew/index.cformation?FuseAction=ShowNews&NewsID=1879.B.StratigraphiccolumnfortheBradburyandMountSharpgroups, includingalldrillholelocations(Grotzingeretal.,2015).C.StratigraphiccolumnoftheMurrayformation,includingthefoursamplinglocationsinthispaper(Grotzingeret al.,2015).

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Fig. 2.Drillholes/targetsforsamplestakenfromtheMurrayformationandanalyzedbyCheMin.CHdrillfinesareredderthanothersamples,consistentwiththegreatest hematiteabundance.MJtargetshowslenticularwhitecrystalformsinthemudstone.TPdrillfinesaregray,andthesurroundingfinelaminationsarevisible.BKdrillfines arebright,consistentwithabundantcrystallineandamorphousSiO2.Drillholedepthsare∼6 cm,andsamplesdeliveredtoCheMinaresourcedfromdepthsof∼5–6 cm.

Images’credit:NASA/JPL-Caltech/MSSS.

DiffractionFile using MDI Jade (Materials Data Incorporated, Liv- ermore, CA) software packages. The data were analyzed further viaRietveldreﬁnementmethods,usingJade.TheRietveldmethod involvesconstructing a modelconsistingof thecrystal structures ofallcomponentphasesandminimizingthe differencesbetween theobserved and simulateddiffraction patternsby varying components of the model, including scale factors (related to phase abundance) and unit-cellparameters. This methodthus provides informationon all well-ordered crystalline phases, butis not di- rectly applicable to disordered phases such as clay minerals or X-rayamorphouscomponents.

Cell parameters for well-crystalline minerals present at

>∼^{5 wt.%} âbundance ^were ^refined ûsing^structure ^files^from^the

AmericanMineralogist Crystal Structure Database.Abundances of phyllosilicate,poorlycrystalline,andXRD-amorphousphaseswere estimatedbytheFULLPATfullpatternﬁttingmethod(Chiperaand Bish,2002) usinglaboratorypatternsgeneratedfromCheMinIV,a laboratoryprototypeoftheCheMinﬂightinstrument.

Major, minor,andsome trace element abundances were mea- suredwiththeAPXSlocatedontheendofCuriosity’sroboticarm (Campbelletal.,2012; Gellertetal.,2015b).TheCheMindrillsam- pleandthedump pilesofpost-sievedsamples arenominallythe samematerial (<150 μm), and, assuch,theseAPXS analyses are thebestcomparisontoCheMinresults.

Chemicalcompositionsofcrystallinecomponentscomprisingat least ∼^{5 wt.%} ôf ^the ^sample ^were êstimated ^from ûnit-cell ^parameters calculated by Rietveld refinement. The calculations are insensitive, however, to trace element substitutions in the min- eralstructures.Inordertolimitartificial“assignments”ofthetrace elementstotheamorphousmaterial,weusedcompositionsofnat- urallyoccurringminerals(fromanalysesofmartianmeteorites)to estimatethetracechemicalcompositionsofthecrystallinephases

>5wt.%(after Morrisetal.,2016).The elementalcompositionof theX-rayamorphous±phyllosilicatecomponentswasestimatedby massbalancecalculationsfromthebulk APXScompositionofthe post-sieveddumppile,theinferredcompositionsofthecrystalline

phases, and the weight proportion of the X-ray amorphous and phyllosilicate components determined by FULLPAT (methods de- tailedbyVanimanetal.,2014;Morrisetal.,2016).

3. Results 3.1. Conﬁdencehills

The Confidence Hills (CH) sample provides our stratigraphi- callylowermostmeasurementofthePahrumpHillssection ofthe Murrayformation. Themajor minerals present(>∼^{5 wt.%} ôf ^the crystalline phases) in this sample in decreasing order of abundance are: plagioclase, hematite, augite, pigeonite, sanidine, and magnetite (Fig. 3, Table 1).The broad diffraction peak near10 Å indicates thepresenceofa poorlycrystalline 2:1-layertype phyllosilicate.Theidentityofthephyllosilicatecannotbe furthercon- strainedbecauseoftheabsenceofadistinct 02peak(e.g.,Vani- manetal.,2014);thepositionofthe001peak,however,isconsis- tent witha collapsedsmectiteorillite(e.g.,MooreandReynolds, 1997). FULLPAT analysis of the CH pattern suggests this sample contains∼^{8 wt.%}^2:1^layer^typephyllosilicate.CHhasthegreatest abundancesofmaficigneousminerals,phyllosilicate,andhematite ofallsamplespresentedinthismanuscript.

Unit-cell parameters (Table 2) of plagioclase are consistent withandesine, An₄₂₍₁₀₎ (Table 3, valuesin parenthesesrepresent 2-sigmaerrors),andthoseofsanidineareinagreementwithhigh sanidine, Ab26(16)Or74(16), with complete Al–Si disorder. We de- rivedapigeonitecompositionofEn60(6)Fs38(7)Wo2(2),however,the derived compositions and relative abundances of the pyroxenes havelargeuncertaintiesbecauseofoverlappingpeaksandthelow angular resolution of the CheMin instrument (0.3^◦2θ; Blake et al., 2012). The magnetite unit cell reﬁned to an a unit-celledge lengthof8.365(6) Å,whichindicates thatmagnetiteisintermedi- atetostoichiometricmagnetiteandmaghemiteifweassumethat Fe is theonly cationin themineral (e.g.,SchwertmannandCor- nell, 2000). The derived formula of magnetite is Fe2.81(5)0.19O4