CorrespondingauthorEmailaddress Icarus2062010269133289 ContentslistsavailableatScienceDirectjournalhomepagewwwelse OMEGAspectraconcludedthattheerodedHesperianlavasurfacesarerichinhighcalciu ID: 838803
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1 AnalysisofphyllosilicatedepositsintheNil
AnalysisofphyllosilicatedepositsintheNiliFossaeregionofMars:ComparisonofTESandOMEGAdataJosephMichalski,FrançoisPoulet,Jean-PierreBibring,NicolasMangoldInstitutdAstrophysiqueSpatiale,Bâtiment121,UniversitéParisSud,OrsayCedex91405,FranceLab
2 .dePlanétologieetGéodynamique,UMR6112,
.dePlanétologieetGéodynamique,UMR6112,CNRSetUniversitédeNantes,2ruedelaHoussinière,BP92208,44322NantesCedex3,France Correspondingauthor.E-mailaddress: Icarus206(2010)269…289 ContentslistsavailableatScienceDirectjournalhomepage:www.else OM
3 EGAspectraconcludedthattheerodedHesperia
EGAspectraconcludedthattheerodedHesperianlavasurfacesarerichinhigh-calciumpyroxene(clinopyroxeneinthecaseofTES),andarelargelybasalticcomposition(Band“eld,2002;Mus-tardetal.,2007;Pouletetal.,2009).Theancientterrainisalsobasaltic,butwithalarger
4 componentoflow-calciumpyroxeneMustardeta
componentoflow-calciumpyroxeneMustardetal.,2007;Pouletetal.,2009).Olivine-bearingterrainsintheeasternpartoftheregion(Hoefenetal.,2003;Mangoldetal.,2007)maybeerodedlava”ows(HamiltonandChristensen,2005;Tornabeneetal.,2008),orcouldrepresentolivi
5 ne-richejectafromtheIsidisimpactbasinloc
ne-richejectafromtheIsidisimpactbasinlocatedtotheeast(Mustardetal.,).TosummarizethegeologyoftheNiliFossaearea,thereisanancient(Noachian),eroded,basalticcrustthatwasmodi“edbyimpact,dissectedtectonically,and”oodedwithSyrtisMajorbasalticlav
6 as(Hesperian);itiswithintheancientcrustt
as(Hesperian);itiswithintheancientcrustthatallofthephyllosilicatesaredetected.Phyllosilicatedepositscorrespondtoavarietyofgeomorphicsurfaces,includinglocallylayeredterrain,massivedeposits,andsurfacesseeminglycutbydikesandfractures(Mangoldetal.,).L
7 owinthestratigraphicsection,thesealterat
owinthestratigraphicsection,thesealterationmineralscorrespondtolayeredandmassiveterrains.Higherinstratigraphicsection,claymineralsareassociatedwithimpactejectaortheoliv-ine-bearingunit(Mustardetal.,2007).Theolivine-bearingunitcontainsbothalteratio
8 nphasesandtherelativelyunstablemineralol
nphasesandtherelativelyunstablemineralolivinemixedatthesubpixellevel,whichmayindicateonlypartialalterationbylocalizedhydrothermalprocesses(Mangoldetal.,).Fromthisperspective,itispossiblethatsomeofthephyllo-silicatesformedinassociationwiththeimpact
9 process(etal.,2007).However,Mustardetal.
process(etal.,2007).However,Mustardetal.(inpress)presentconvincingcasesthat(1)mostofthephyllosilicatesassociatedwithejectaex-istwithinexcavatedblocksoflayeredrocksand(2)theolivine-bearingunitalsocorrespondsadrapingejectadeposit.Therefore,itappears
10 thatthediversemelangeofprimaryandseconda
thatthediversemelangeofprimaryandsecondarysili-catesintheNiliFossaeregionexistbecauseoferosionalwindowsintothealteredandoftenlayereduppercrust,andbecauseoftheexcavationofthecrustbyimpact.BasedonOMEGAdata,phyllosilicatesdetectedintheNiliFossaeregio
11 nareinterpretedaspredominantlyFe/Mg-rich
nareinterpretedaspredominantlyFe/Mg-richsmectiteclayminerals.Insomecases,thespectraindicatenontronite-likeclaysandinothercases,Mg-richsmectites(Pouletetal.,2005,2008;Man-goldetal.,2007).Thisinterpretationisbasedonthecombinedoccur-renceofspectralab
12 sorptionsrelatedtoH…O…H(interp
sorptionsrelatedtoH…O…H(interpretedasinterlayerwaterinexpandableclays)at(=)1.9m,octahedral(Fe/Mg)…OHnear2.3m,andtheoverallspectralshapeofthephyl-losilicate-bearingsurfaces.Thevariablespectralshapeofthedepos-itsinOMEGAdataseemstoindi
13 catethatmultiplespeciesofclaymineralsare
catethatmultiplespeciesofclaymineralsarepresentthroughouttheregion,orthatasinglealter-ationphase(Fe/Mgsmectite)ispresentwithvariablecrystalchem-istry(moreorlessMgorFeindifferentdeposits).However,CRISMresultshaveshownamuchlargersuiteofalterationpha
14 ses,includ-ingkaolinite,chlorite,analcim
ses,includ-ingkaolinite,chlorite,analcime,lizardite,illiteormuscovite,hy-dratedsilica,Mg-carbonate,andotherunidenti“edalterationphases,occurringinsmall,scattereddepositsthroughouttheregionEhlmannetal.,2008,inpress).Manyofthedepositscouldbeint
15 er-pretedassedimentary,volcanoclastics,o
er-pretedassedimentary,volcanoclastics,orimpactiterocksbecausetheyarelayeredandintenselyaltered,butotherclassesofrocksmayalsobepresent.Associatedwiththecentralupliftofseveralcra-tersintheregionisaspectralsignatureattributabletopumpellyiteoraprehni
16 te,whichmayrepresentexcavationofthemetam
te,whichmayrepresentexcavationofthemetamorphiccrustofMarsfromdepth(Pouletetal.,2008Ehlmannetal.,inpressTheuseofthermalinfraredspectrainthisstudybringsanewmineralogicalperspective,albeitwithlowerspatialandspectralresolutiondata.Thissiteiswellsuited
17 foracombinedspectro-scopicapproachbecaus
foracombinedspectro-scopicapproachbecausethesurfacesaroundNiliFossaearegeo-logicallycomplexandrelativelydust-free(Fig.2RuffandChristensen,2002).Inthethermalinfrared,itispossibletodetectFe-poor,anhydrousphasesthatarenotdetectableinthenearinfrared(s
18 uchassilicamineralsandfeldspars).Inaddit
uchassilicamineralsandfeldspars).Inaddition,theperspectiveonclaymineralogyisdifferentinthethermalinfraredcomparedtothenearinfrared.Inthethermalinfrared,thespectralfeaturesofphyllosilicatesaredominatedby(Si,Al)…Ostretchingandbending,andSi…
19 ;O…(Fe,Mg,Al)deformationscorrespond
;O…(Fe,Mg,Al)deformationscorrespondingtotetrahedralsheetsandthebondsbetweentetrahedralandocta-hedralsheets(Michalskietal.,2006a).Bycontrastinthenearinfrared,thedominantspectralfeaturesaremostlyrelatedto Fig.1.MOLAtopographicmap(left)showingth
20 eregionalcontextoftheNiliFossaeregion.Ar
eregionalcontextoftheNiliFossaeregion.Aregionalgeologicmap(Skinneretal.,2006)showingthegeologicsettingoftheNiliFossaearea.Mapunitsinclude:Nple,Noachianplateausequence…etchedunit;Nplz,Noachianplateausequence…subduedcraterunit;Npld,Noachia
21 nplateausequence…dissectedunit;HNu,
nplateausequence…dissectedunit;HNu,Hesperian…Noachianundividedmaterials;Hs,HesperianSyrtisMajorFormation;Hvr,HesperianVastitasBorealisFormation;Apk,Amazonianknobbyplainsmaterials;cs,impactcratermaterials.J.Michalskietal./Icarus206(2010)2