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Early martian surface conditions Early martian surface conditions from thermodynamics of from thermodynamics of
phyllosilicatesphyllosilicates
Vincent F. ChevrierVincent F. Chevrier
Workshop on Martian Phyllosilicates:Recorders of Aqueous Processes?
Paris, October 21-23, 2008
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Why?Why?
Access to surface / subsurface conditionsAccess to surface / subsurface conditions Environmental conditions: acidity, oxidation, Environmental conditions: acidity, oxidation,
temperaturetemperature Bedrock compositionBedrock composition AtmosphereAtmosphere
Evolution of the surfaceEvolution of the surface
Feedback for spectral data analysisFeedback for spectral data analysis Spectroscopy gives what there isSpectroscopy gives what there is Equilibrium give what are the paragenesesEquilibrium give what are the parageneses Especially what should Especially what should NOTNOT be there be there
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PlanPlan
1 – Geochemical modeling1 – Geochemical modeling
2 – Stability conditions of smectites2 – Stability conditions of smectites
3 – CO3 – CO22 in the Noachian atmopshere in the Noachian atmopshere
4 – Phyllosilicates and sulfates4 – Phyllosilicates and sulfates
5 – Effect of temperature5 – Effect of temperature
6 – Conclusions6 – Conclusions
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1. Geochemical 1. Geochemical modelingmodeling
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Phyllosilicate diversityPhyllosilicate diversity
Wavelength (m)
Montmorillonite
Hyd. silica
Mg/Fe Smectite
Illite / Chlorite
Kaolinite
Muscovite
Mustard et al., 2008
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Geochemical modelingGeochemical modeling
Primary phases
(Cpx, Pg, ol)
Total rock composition
(no transport)
Solution composition
Secondary phases
Smectite, kaol, silica…
Precipitation model
T, pH, pe, atm
Dissolution model
T, pH, pe, atm
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Starting compositionStarting compositionSpecie Conc. (mg L-1) Log (activity)
SiO2 60.1 -4.5
Al3+ 1 -4.4
Fe2+/3+ 44.7 -3.1
Mg2+ 24.3 -3.0
Ca2+ 20 -3.3
Na+ 18.4 -3.1
K+ 2.7 -4.2
Cl- 23 -3.2
SO42- 17.3 -3.7
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Equilibrium simulationsEquilibrium simulations
Geochemical workbench software Geochemical workbench software packagepackage
thermo_phrqpitzthermo_phrqpitz basic database basic database
Updated with ferric species and Pitzer Updated with ferric species and Pitzer coefficients (for high concentrations)coefficients (for high concentrations)
Updated with ~300 silicate phases Updated with ~300 silicate phases ((thermo.com.v8.r6+thermo.com.v8.r6+))
Total number of phases for equilibrium Total number of phases for equilibrium calculations: 395calculations: 395
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2. Stability conditions 2. Stability conditions of smectitesof smectites
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Nontronite stabilityNontronite stability
•Slightly acidic to Slightly acidic to high pHhigh pH
•High oxidation High oxidation levelslevels
•Weak effect of Weak effect of temperature (from temperature (from 298 to 373K)298 to 373K)
Chevrier et al., 2007, Nature
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Mineral controlMineral control
Noachian terrains Noachian terrains (OMEGA)(OMEGA)
Primary phasesPrimary phases Hedenbergite = FeHedenbergite = Fe2+2+
Diopside = MgDiopside = Mg2+2+
Anorthite = AlAnorthite = Al3+3+
High pH (> 6)High pH (> 6)
Formation of ripidolite Formation of ripidolite (var. clinochlore) at (var. clinochlore) at low pHlow pH
Fe2+2Al2SiO5(OH)4
Clinochlore
(Mg,Fe2+)5Al2Si3O10(OH)8
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Aluminum phasesAluminum phases
• Transition of saponite to montmorillonite to Transition of saponite to montmorillonite to kaolinite with decreasing pHkaolinite with decreasing pH
• Muscovite can form at neutral pH if KMuscovite can form at neutral pH if K++ increases increases
Log aLog aK+K+ = -4.2 = -4.2 Log aLog aK+K+ = -2 = -2
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Smectites formationSmectites formation
High water to rock ratioHigh water to rock ratio
Weakly acidic to alkaline pH (6 to 12)Weakly acidic to alkaline pH (6 to 12)
High oxidation (for nontronite)High oxidation (for nontronite)
High silica activity (log SiOHigh silica activity (log SiO22 = -4 to -5) = -4 to -5)
Variations depend on activity of other Variations depend on activity of other cations Fe, Mg, Ca, Al, K, Nacations Fe, Mg, Ca, Al, K, Na
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3. CO3. CO22 in the in the
Noachian atmosphereNoachian atmosphere
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Evaporation simulationsEvaporation simulationsStandard conditionsStandard conditions
•ppCO2CO2 = 6 mbar = 6 mbar
•pH ~ 6-7pH ~ 6-7
•ClCl-- = 120 mg/kg = 120 mg/kg
•pe = 13.05 pe = 13.05 (Fe(Fe2+2+/Fe/Fe3+3+))
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Evaporation simulationsEvaporation simulationsHigh pHigh pCO2CO2
•ppCO2CO2 = 1 bar = 1 bar
•pH ~ 5 to 7pH ~ 5 to 7
•Cl = 23 mg/kgCl = 23 mg/kg
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Evaporation simulationsEvaporation simulationsAl – system - High pAl – system - High pCO2CO2
•ppCO2CO2 = 1 bar = 1 bar
•pH ~ 5 to 7pH ~ 5 to 7
•Cl = 23 mg/kgCl = 23 mg/kg
•Fe = 0.45 kg/kgFe = 0.45 kg/kg
•Al = 10 mg/kgAl = 10 mg/kg
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COCO22 in the Noachian in the Noachian atmosphereatmosphere
pe = 5
CO2 pulse
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Carbonates on MarsCarbonates on Mars
May have formed on MarsMay have formed on Mars
Same pH conditions as for Same pH conditions as for phyllosilicatesphyllosilicates
Mainly dolomite and magnesiteMainly dolomite and magnesite
Need some evaporation processNeed some evaporation process
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4. Phyllosilicates and 4. Phyllosilicates and sulfatessulfates
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Presence of sulfatesPresence of sulfates
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Evaporation simulationEvaporation simulationStandard solutionStandard solution
•ppCO2CO2 = 6 mbar = 6 mbar
•ClCl-- = 120 mg/kg = 120 mg/kg
•SOSO442-2- = 17.3 = 17.3
mg/kgmg/kg
•pe = 13.05pe = 13.05
•pH ~ 6pH ~ 6
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Evaporation simulationEvaporation simulationsulfur rich conditionssulfur rich conditions
•ppCO2CO2 = 6 mbar = 6 mbar
•pH = 2.5 to 1pH = 2.5 to 1
•ClCl-- = 120 mg/kg = 120 mg/kg
•SOSO442-2- = 173 = 173
mg/kgmg/kg
•pe = 13.05pe = 13.05
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Evaporation processEvaporation processConcentrated solutionsConcentrated solutions
•ppCO2CO2 = 6 mbar = 6 mbar
•pH ~ 1pH ~ 1
•SOSO442-2- = 5000 = 5000
mg/kgmg/kg
•All other All other concentration concentration x10x10
•pe = 13.05pe = 13.05
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Impact of sulfateImpact of sulfate
Strong decrease of the pH (7 to 1)Strong decrease of the pH (7 to 1)
Inhibition of smectite formationInhibition of smectite formation
First phases to disappear: First phases to disappear: carbonatescarbonates
Precipitation of sulfatesPrecipitation of sulfates
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5. Effect of 5. Effect of temperaturetemperature
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Stability diagramsStability diagrams
• Nontronite stable at low TNontronite stable at low T
• At higher temperature: chlorite in more reducing At higher temperature: chlorite in more reducing environments, ferrihydrite (hematite) at lower pHenvironments, ferrihydrite (hematite) at lower pH
pe = 13.05 pe = 13.05 pH = 7pH = 7
Clinochlore
Mg-chlorite
Fe2+-chlorite
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Temperature effectTemperature effectOxidant conditionsOxidant conditions
•ppCO2CO2 = 6 mbar = 6 mbar
•pe = 13.05pe = 13.05
•pH = 7pH = 7
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Temperature effectTemperature effectReducing conditionsReducing conditions
•ppCO2CO2 = 6 mbar = 6 mbar
•pe = 0pe = 0
•pH = 7pH = 7
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Effect of temperatureEffect of temperature
Nontronite destabilizationNontronite destabilization
Formation of FeFormation of Fe2+2+-Mg-phyllosilicates -Mg-phyllosilicates (minnesotaite, chlorite)(minnesotaite, chlorite)
Formation of FeFormation of Fe2+2+-Mg serpentine -Mg serpentine minerals (talc, antigorite)minerals (talc, antigorite)
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6. Conclusions6. Conclusions
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Phyllosilicate Phyllosilicate stratificationstratification
• Al-rich phyllosilicateAl-rich phyllosilicate
• Kaolinite and Kaolinite and montmorillonitemontmorillonite
• FeFe2+2+ + hydrated silica + hydrated silica
• FeFe3+3+/Mg/Mg2+2+ smectites smectites
• Temperature changesTemperature changes• Aqueous chemistry change (pH, oxidation)Aqueous chemistry change (pH, oxidation)• Atmosphere evolutionAtmosphere evolution• Bedrock variationBedrock variation
Bishop et al., 2008
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Mineralogical Mineralogical relationshiprelationship
Fe-Mg smectitesFe-Mg smectites
CarbonatesCarbonates
MontmorilloniteMontmorillonite
KaoliniteKaolinite
FeFe2+2+ phyllosilicatesphyllosilicates
SulfatesSulfates
pH decreasepH decrease
COCO22
TemperatureTemperature
Al / Fe activityAl / Fe activity
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Phyllosilicate Phyllosilicate stratificationstratification
Acidity changeAcidity change Kaolinite records transition to acidic Kaolinite records transition to acidic
conditions?conditions? Compatible with the “varnish” aspect of the Compatible with the “varnish” aspect of the
depositsdeposits Compatible withCompatible with
Temperature increaseTemperature increase Locally possibleLocally possible Problem withProblem with absence of serpentine absence of serpentine
mineralsminerals
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ProblemsProblems
Pure phases in calculationsPure phases in calculations Clays are “geochemical trashcans”Clays are “geochemical trashcans” Some thermodynamic properties are not Some thermodynamic properties are not
knownknown
Does not take into account kineticsDoes not take into account kinetics
Necessity for clear identification of what is Necessity for clear identification of what is presentpresent
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Some solutionsSome solutions= Future work= Future work
Determination of water compositionsDetermination of water compositions Equilibrium with primary rocksEquilibrium with primary rocks
Kinetics of the processesKinetics of the processes
Necessity for experimentsNecessity for experiments Kinetic constantsKinetic constants Transitory metastable phasesTransitory metastable phases Verification of modelsVerification of models