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
Jan 15, 2016
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