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H. Clenet, C. Quantin, M. Andreani and P. Allemand

29/02/2012, Washington

CARBONATE-BEARING CRUSTAL EXPOSURE IN AN IMPACT CRATER ASSOCIATED WITH AN

OUTFLOW CHANNEL CONTEXT

harold.clenet@univ-lyon1.frcathy.quantin@univ-lyon1.fr

Regional context

Map from Edwards et al., 2008, JGR

Proposed landing site

Olivine layer in Eos Chasma

Mineralogy in thecentral peak

R : LCPINDEX    [0.05-0.14]G: HPCINDEX   [0.05-0.23]B: OLINDEX      [0.005-0.05]

From Ehlmann et al., 2008

« Direct » carbonation reactionsForsterite → Magnésite

Fayalite→ Sidérite

Enstatite → Magnésite Ferrosilite → Sidérite

Diopside → Dolomite

High PCO2

3𝐹𝑒2𝑆𝑖𝑂4+𝑆𝑖𝑂2+2𝐻 2𝑂→2𝑀𝑔3𝑆𝑖2𝑂5(𝑂𝐻 )4

Serpentinization of olivine (fayalite + aqueous silica = serpentine)

2𝑀𝑔3𝑆𝑖2𝑂5(𝑂𝐻 )4+3𝐶𝑂2→𝑀𝑔3 𝑆𝑖4𝑂10(𝑂𝐻 )2+3𝑀𝑔𝐶𝑂3+𝐻 2𝑂Carbonation of serpentine (serpentine + CO2 = talc + magnésite)

Serpentine and carbonation reactions

Low PCO2

Circulation of fluids enriched in CO2

High PCO2

then

© IPGP (CNRS, Univ Paris Diderot)/Università di Modena e Reggio EmiliaMenez et al., Nature Geoscience 2012

Blue=hydrogarnet (Ca3Al2(SiO4)3-x(OH)4x)Green=serpentinized pyroxeneRed=Ferric oxydeYellow=organic molecules

Serpentinization of olivine (forsterite + H2O = serpentine + brucite + magnetite)

2𝑀𝑔3𝑆𝑖2𝑂5(𝑂𝐻 )4+3𝐶𝑂2→𝑀𝑔3 𝑆𝑖4𝑂10(𝑂𝐻 )2+3𝑀𝑔𝐶𝑂3+𝐻 2𝑂Carbonation of serpentine (serpentine + CO2 = talc + magnésite)

Serpentine and carbonation reactions

𝑀𝑔1,8 𝐹𝑒0,2𝑆𝑖𝑂4+1,37𝐻2𝑂→0,5𝑀𝑔3𝑆𝑖2𝑂5(𝑂𝐻 )4+3𝑀𝑔(𝑂𝐻 )2+0,067𝐹𝑒3𝑂4 +0,067𝐻 2

Low PCO2

High PCO2

then

Habitability?

Circulation of fluids enriched in CO2

Hydrothermal system Hesperian aqueous activity

Emplacement of the mafic unit

Post-impact process

?

Paleolake induced deposits

High T° Low T°

Landing contraints

Elevation

Slope

Conclusion

-Primitive martian crust

-Putative hydrothermal system and its exobiological niches

-Outflow channel context