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 79001Catling (2007) Nature, 448, 31-32.

clays

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

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?

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

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.

METHOD FOR CLAY MINERALOGY

0

50

100

150

200

250

300

350

400

450

500

59 60 61 62 63 64

inte

nsi

té

1.54 Å

1.53 Å1.52 Å

1.49 Å

°2 Cu K

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

3 4 5 6 7 8 9

inte

nsi

té

14.97 Å

14.84 Å

14.02 Å

°2 Cu K0

500

1000

1500

2000

2500

8 9 10 11 12 13 14 15

inte

nsi

té

7.38 Å

7.21 Å

°2 Cu K

0

200

400

600

800

1000

1200

1400

8 9 10 11 12 13 14 15

inte

ns

ité

8.40 Å 7.60 Å

7.20 Å

°2 Cu K0

2000

4000

6000

8000

10000

12000

3 4 5 6 7 8 9

inte

ns

ité

16.66 Å

15.98 Å

14.02 Å

°2 Cu K

air dried

glycol

0

100

200

300

400

500

600

3 5 7 9 11 13 15

intensité

14.11 Å

12.48 Å10.08 Å

7.17 Å

°2 Cu K °2 Cu K

0

50

100

150

200

250

300

350

400

450

500

3 5 7 9 11 13 15

inte

nsi

té

15.05 Å

14.02 Å

10.39 Å7.17 Å

heated 300°C

X-ray diffraction

M+

/4S

i

celadonite

chlorite

nontronitesaponite

0

0 ,2

0 ,4

0 ,6

0 ,8

1

0 0 ,2 0 ,4 0 ,6 0 ,8 1

Fe/sum Oct

nontronite+ chlorite+saponite

Electron microprobe analyses

0.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

2.1

2.3

2.5

400140024003400

nombre d'onde (cm-1)

inte

nsi

té

3570

Fe3+-Fe3+-OH

1110Si-O

506

Si-O-Fe3+

IR spectroscopy

ALTERATION MICROTEXTURE – 1 – the zoning

zeolites

clays

palag.

unalt. glass

SUBAERIAL FLOW

20µm

zeolites

clays palagonite

unaltered glass

altered olivine

SUBMARINE FLOW

20 µm

Alteration occurs along fractures in the massive glass of the chilled margins

GLASSY MARGIN OF THE SUBMARINE FLOW

Sap80/Chl20 + No55/Chl45 + Chl

altered glassTi oxides

Fe-rich clays

Fe-Mg clays

zeolites10 µm

ALTERATION MICROTEXTURE – 2 – the retreating glass surface

altered glass

Ti oxides

10 µm

GLASSY MARGIN SUBAERIAL FLOW

Saponite + nontronite

alt. glass

glass

plapla

zeolites

clays

10 µm

Fe-rich clays

Mg-rich clays

plagioclasealt. glass

plagioclase

plagioclase 10 µm

ALTERATION MICROTEXTURE – 3 –organization of the clay particles

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

initial fracture zeolite

Mg-clays

Fe-clays

palagonite

unaltered glass

retreatingsurface

Ti-oxides

first interface

final interface

fracture volume

dissolved volume

THE FORMATION OF CLAYS BY GLASS ALTERATIONa possible model

MESOSTASIS AND DIKTYTAXITIC VOIDS

20µm

pl

px

opap

px

px

10 µm

mesostasis

mesostasis

1- Nucleation of the phenocrysts

2- growth of the phenocrysts - Filter press

3- Formation of a glass from the residual liquid

MESOSTASIS

MAGMA

DIKTYTAXITIC VOIDS

pyroxene

plagioclase

olivine MAGMA

Example: the subaerial lava flow (Mururoa)

MESOSTASIS - AERIAL LAVA FLOW (HAWAIITE)1 – clay microtexture

Sap55/Chl45 + Sap22/Chl78 + Ce

20µm

biocpx

alt. ol

K-fels

plapla

mes

mes

alt. ol

10 µm

biotiteCe + Mg-clays

K-fels

cpx

Surprisingly, clays grow on unaltered biotite surfaces.

To what process this zoning is related?

pla

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

1st step: non-oriented crystal growth

2nd step: center-oriented crystal growth

MESOSTASIS - AERIAL LAVA FLOW (HAWAIITE)2 – the geometrical selection (Grigor’ev D. P., 1965)

MESOSTASIS - SUBAERIAL LAVA FLOW (HAWAIITE)clay microtexture

Sap + Sap35/Chl65 + Cel No alteration features on the clay-apatite or clay-K-feldspar contacts. 1- Apatite and K-feldparco-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

MESOSTASIS - SUBMARINE LAVA FLOW (BASALT)microtexture of clay deposits

px px

clays

clays pla

10 µm

Sap70/Chl30 + No30/Chl70 + 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.

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

plfelds-K

ap

cpx

10 µm

clays

10 µm

clays

ap

cpx

No(2Gl)35/No(1Gl)65 + Ce67/No33 + Sap

microgeoda

diktytaxitic voids

MESOSTASIS – DYKE (HAWAIITE)2 – microtexture of clay deposits in microgeoda

10 µm

10 µm

apatite clays

no glass precursor but a boiling residual solution.

plagioclase

CPX

palissadic microtexture: direct precipitation from an over-saturated solution

AERIAL SUBAERIAL

co-precipitation from a solution? precipitation in a boiling solution

clays

apatite

CPX

plagioclase

clays

SUBMARINE

free space

apatite needle

clay coating

CPX

plagioclase

DYKE

pyroxene

claysCPX

plagioclase

CONCLUSION

1 - no glass precursor2 - 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.

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