1. DO POST-MAGMATIC CLAYS EXIST? HydrASA - University of Poitiers - INSU CNRS Alain MEUNIER, Antoine MAS, Daniel BEAUFORT, Patricia PATRIER & Patrick DUDOIGNON 20 µm Lafayette Mars meteorite EETA 79001 Catling (2007) Nature, 448, 31-32. clays

2. Phyllosilicates on Mars – implication on early climate. Poulet et al. (2005) Nature, 438, 623-627; Nontronite as indicator of alteration by liquid water Chevrier et al. (2007) Nature, 448, 60-63. NONTRONITE ON MARS ’SURFACE

3. TO ANSWER THAT QUESTION NEEDS TO STUDY TERRESTRIAL BASALTIC ANALOGUES. Microtextures can be used as signatures of the origin of clays. The goal of the present study is to compare the clay microtextures which undoubtedly result from an alteration process with those forming the mesostasis in the massive inner parts(diktytaxitic voids). Is the first term of the following equation realistic or too simplistic : clays = alteration = presence of liquid water = life? In other words: do nontronite in basaltic rocks systematically result from an alteration process?

4. WHAT IS TYPICALLY A GLASS ALTERATION TEXTURE? Drief A. & Schiffman P. (2004). Clays Clay Mineral, 52, 622-634. Crystallization of clay minerals at the fluid-glass interface (large particles – geometrical selection). INTERFACE-TYPE ALTERATION Crystallization of clay minerals in the altered glass (small particles – randomly distributed) INNER-TYPE ALTERATION

5. The volcanic rock basalt-hawaiite series from Mururoa atoll give an opportunity to compare the origin of Fe-rich clay minerals (nontronite- like) in different geological environments: 1 - alteration zones of basaltic glass (chilled margins of volcanic bodies) 2 - mesostasis (diktytaxitic voids) of the massive inner parts THE MURUROA ATOLL (FRENCH POLYNESIA): a potential terrestrial analogue 4 volcanic bodies: - aerial flow, - subaerial flow, - submarine flow, - dyke.

6. METHOD FOR CLAY MINERALOGY °2  Cu K  air dried glycol °2  Cu K  heated 300°C X-ray diffraction Electron microprobe analyses IR spectroscopy

7. ALTERATION MICROTEXTURE – 1 – the zoning zeolites clays palag. unalt. glass SUBAERIAL FLOW 20µm zeolites clayspalagonite unaltered glass altered olivine SUBMARINE FLOW 20 µm Alteration occurs along fractures in the massive glass of the chilled margins

8. GLASSY MARGIN OF THE SUBMARINE FLOW Sap 80 /Chl 20 + No 55 /Chl 45 + Chl altered glass Ti oxides Fe-rich clays Fe-Mg clays zeolites 10 µm ALTERATION MICROTEXTURE – 2 – the retreating glass surface altered glass Ti oxides 10 µm

9. GLASSY MARGIN SUBAERIAL FLOW Saponite + nontronite alt. glass glass pla zeolites clays 10 µm Fe-rich clays Mg-rich clays plagioclase alt. glass plagioclase 10 µm ALTERATION MICROTEXTURE – 3 –organization of the clay particles

10. Initial fluid/glass interface Mg-clays grow outwards in the free space Fe-clays grow inwards follwing the retreating surface Ti-oxides accumulate on the dissolution surface of the glass first interface final interface fracture volume dissolved volume THE FORMATION OF CLAYS BY GLASS ALTERATION a possible model

11. MESOSTASIS AND DIKTYTAXITIC VOIDS 20µm pl px op ap px 10 µm mesostasis Example: the subaerial lava flow (Mururoa)

12. MESOSTASIS - AERIAL LAVA FLOW (HAWAIITE) 1 – clay microtexture Sap 55 /Chl 45 + Sap 22 /Chl 78 + Ce 20µm bio cpx alt. ol K-fels pla mes alt. ol 10 µm biotite Ce + Mg-clays K-fels cpx Surprisingly, clays grow on unaltered biotite surfaces. To what process this zoning is related? pla

13. The geometrical selection pattern is typical of crystal growth in free space not of glass inner alteration-type. Why? Possibly, no glass precursor, that is to say, no alteration. K-felds celadonite + Mg-clays 10 µm large particles small particles 1 st step: non-oriented crystal growth 2 nd step: center-oriented crystal growth MESOSTASIS - AERIAL LAVA FLOW (HAWAIITE) 2 – the geometrical selection (Grigor’ev D. P., 1965)

14. MESOSTASIS - SUBAERIAL LAVA FLOW (HAWAIITE) clay microtexture Sap + Sap 35 /Chl 65 + Cel No alteration features on the clay-apatite or clay- K-feldspar contacts. 1- Apatite and K-feldpar co-precipitation in free space; 2- clay nucleation and growth on all the crystal surfaces. K-fels ap clays 10 µm Palissadic texture Possibly, no glass precursor

15. MESOSTASIS - SUBMARINE LAVA FLOW (BASALT) microtexture of clay deposits px clays pla 10 µm Sap 70 /Chl 30 + No 30 /Chl 70 + Cel No alteration features on the clay-pyroxene or clay-plagioclase contacts. co- precipitation in free space of pyroxene and clays (Decarreau et al., 2004). The presence of a glass precursor is not discarded but chemically unprobable.

16. 1 - The diktytaxitic voids are partially filled by the clay-rich mesostasis. Their central part remains empty. 2 – The thickness of the clay coating varies with the size of the diktytaxitic void. MESOSTASIS – DYKE (HAWAIITE) 1 – microgeoda and diktytaxitic voids pl felds-K ap cpx 10 µm clays 10 µm clays ap cpx No(2Gl) 35 /No(1Gl) 65 + Ce 67 /No 33 + Sap microgeoda diktytaxitic voids

17. MESOSTASIS – DYKE (HAWAIITE) 2 – microtexture of clay deposits in microgeoda 10 µm apatite clays no glass precursor but a boiling residual solution.

18. CONCLUSION 1 - no glass precursor 2 - no alteration CLAYS PRECIPITATED DURING THE POST- MAGMATIC STAGE DIRECTLY FROM THE RESIDUAL FLUIDS TRAPPED IN THE DIKTYTAXITIC VOIDS. CONSEQUENTLY, LIQUID WATER DID NOT FLOW INSIDE BUT ESCAPE OUTSIDE THE LAVAS AS VAPOR.

19. Because the presence of nontronite does not mean that water has circulated inside the basaltic rocks, it may be better to chose another criterium for the future Mars landing sites. It should be safer to select areas where other clays are detected (kaolinite for instance). To that point, it is even more important to study terrestrial analogues. SO WHAT? … Crédit : NASA/JPL/JHUAPL/University of Arizona/Brown University. clays