clay minerals in returned samples and … · right: hpf/freeze-etched, ... holland, p. 231-247. •...

CLAY MINERALS IN RETURNED SAMPLES AND ALTERATION

CONDITIONS ON MARS or

What do we know about what clay minerals can tell us about alteration

conditions on Mars?

Michael A. Velbel

What can clays (in samples) tell us?

•

Parent materials•

Geochronology of aqueous alteration

•

Alteration processes (primary-mineral corrosion-replacement; mechanisms)

•

Clay-mineral composition and elemental transfer during alteration

•

Preservation potential of informative clay- mineral related textures

What can clays tell us?

•

Parent materials•

Geochronology

•

Alteration processes

(primary-mineral corrosion-replacement; mechanisms); equilibrium & disequilibrium

•


•


Process-product

•

Nature:•

Process (conditions) → Product

•

Science:

Work back from observed products to infer processes

•

Process ← Scientific Inference ← Observed Product•

Our question: How to infer past processes & conditions (e.g., properties of solutions that are no longer present) from observations of solid products?

Clay-solution equilibrium

Chevrier & al. (2007) Nature, v. 448 p. 60

Thermodynamic approach• Many published papers

and several previous talks at this workshop use equilibrium thermodynamic stability diagrams.

• On Earth, kinetics dominate below ~60°C, equilibrium obtains above ~100°C. (Lasaga, 1984, JGR).

• Partial equilibrium – disequilibrium -

kinetics

for “low-T” systems.

Velbel (1985) in Drever, J.I. (editor), The Chemistry of Weathering, NATO-ARW.

Clay-solution partial equilibrium

Velbel (1985) in Drever, J.I. (editor), The Chemistry of Weathering, NATO-ARW.

Partial equilibrium & kinetics: Closed system

•

Partial equilibrium•

Reaction progress

•

Reaction path•

Primary-mineral dissolution kinetics

•

Secondary-mineral precipitation & dissolution kinetics

Steinmann & al. (1994) Clays & Clay Minerals, v. 42 p. 197

Partial equilibrium and reaction progress

•

K-feldspar to solutes (congruent):•

2KAlSi3

O8

+ 2H+

+ 14H2

O 2K+ + 2Al(OH)3° + 6H4SiO4(aq)

•

As this K-feldspar dissolves:•

Some acid

is consumed, raising pH

•

Potassium ion, silica, and dissolved Al are produced

•

[K+]/[H+] & [H4

SiO4(aq)

] increase•

Eventually, gibbsite is produced


•

Starting w/dilute mildly acidic water

•

(low pH, low dissolved K, Si)

•

Kinetically limited dissolution of K-spar consumes H (raises pH), produces K, Si

•

Eventually, kaolinite is produced



•

Solution evolves from lower left to upper right

•

Sequence of secondary minerals forms as solution evolves toward equilibrium w.r.t. primary mineral



•

Specific reaction path, and specific sequences of products formed, depend on initial values of pH and initial activities of other dissolved species


Specific reaction path, and specific sequences of products formed, also depend reactant dissolution

kinetics and product precipitation kinetics

Lasaga (1998) Kinetic Theory in the Earth Sciences, ch. 1

Partial equilibrium & kinetics: Open system

•

If water is moving (e.g., through regolith or weathering rind) while reacting (kinetically) with K-

feldspar,•

sequence of secondary minerals forms in space (“weathering profile”) rather than time.


Partial equilibrium and kinetics: Summary

•

Clays formed by weathering vary with the interplay between

•

(1) the dissolution kinetics of primary minerals that release silica and cations to solutions (and

consume acid) and •

(2) the leaching intensity

of the weathering

environment•

Info on both (kinetically inhibited) primary minerals and (partial equilibrium) secondary minerals is required to draw inferences about solution composition and leaching intensity

Info from solid-phase samples

•

Mineral assemblages•

Mineral associations (pseudomorphic, contact)

•

Reactant corrosion-replacement textures•

Secondary-mineral distributions, textures

•

Product compositions (major-element, minor-/trace-element, isotopic)

•

Parent-product compositional relations


•

Parent materials•

Geochronology

•


•


•


Elemental transfer during px

alteration: Koua Bocca volumetrics

(Velbel & Barker, 2008)

Reactant-product pair

Elementconserved Vp

/Vr

Cpx-expanded smectite Si 1.76

Fe 0.49

Cpx-collapsed smectite Si 1.03

Fe 0.28

Opx-expanded smectite Si 1.82

Fe 1.14

Opx-collapsed smectite Si 1.06

Fe 0.66

Top: Eggleton (1975), American Mineralogist, v. 60, p. 1063-1068. Bottom: Koua Bocca Complex px, XPL (cf Delvigne, 1998, image #293); frame is 1.5 mm wide.

Koua Bocca volumetrics: Si conservation during early px

w’th’g

•

Weathering of both cpx

& opx

isovolumetric

•

Si minimally mobile•

Consistent with structural inferences (Eggleton, 1975; Cole and Lancucki, 1976) and TEM observations (Eggleton and Boland, 1982; Banfield and Barker, 1994).

•

Fe transfer from opx

&/or ol

to cpx

products is

required•

Velbel & Barker (2008)

Top: Eggleton (1975), American Mineralogist, v. 60, p. 1063-1068. Bottom: Koua Bocca Complex px, XPL (cf Delvigne, 1998, image #293); frame is 1.5 mm wide.


•

Parent materials•

Geochronology

•


•


•


Primary-mineral corrosion textures and clay-mineral textures

Air-dried, conventional SEM. Left:

Velbel

(2007) Fig. 1B. Right:

Velbel

& Barker (2008) Fig. 2b. Scale marks in both10 μm apart.

Clay textures: Low preservation potential

• Clay minerals formed as weathering product of pyroxene are strongly modified by environmental excursions during sample handling & preparation.

• Hydrous phases will be highly informative about Martian surface conditions, but also highly vulnerable to excursions in T, r.h.,

&c. during sample acquisition, recovery, return and curation.

Left: Air-dried, SEM (Velbel

& Barker, 2008, Fig. 4); clay shrunken, bunched-up, pulled away from clean pyroxene

denticles. Scale marks 10 μm apart.Right: HPF/freeze-etched, FEG-SEM (Velbel

& Barker, 2008, Fig. 19); clay in space-filling “house-of-cards”

arrangement, w/clay-

coated

denticle

at bottom.

Alteration-product textures in Mars meteorites –

and returned samples?

Low preservation potential

Thermally decrepitated hydrous minerals near fusion crust in Nakhla. Left: Mg-sulfate. Right: Iddingsite. Both from Wentworth & al. (2005), Icarus, v. 174, p. 382Icarus, v. 174, p. 382--395.395.

Pyroxene corrosion textures: High preservation potential

• The pyroxene surface is unaffected by r.h. changes during sample handling and examination.

• Corrosion and replacement textures at interfaces between anhydrous igneous minerals and their neighbors (including alteration products and exposed surfaces) will be much less vulnerable to modification by the sample recovery-return process.

• Image: Air-dried preparation. From

Velbel

(2007), Fig. 5a (SEM). Scale marks are 10μm apart.

Moldic

porosity implying removal by dissolution/weathering of

euhedral

reactants: High preservation potential

(L) Unidentified

evaporite

mineral at

Meridiani Planum

(MER-B MI; NASA Planetary Photojournal

image PIA05476; Squyres

& al 04)(R)

Euhedral

olivine at

Gusev

Crater (MER-A MI; “Composite MI image (no. 2M131690279EFF1155P2939M2M1) of an oblique RAT grind into Humphrey, illustrating its natural surface containing

hexagonal casts …. The view is ~3 cm wide.”

From McSween et al. (2004), Science v. 305, p. 842-845.)

Preservation potential

• High-preservation potential textures (e.g., left) are likely “survivors” of sterilization and/or thermal excursions during sample return,

either intentionally in a low-budget “quick-release” mission with limited environmental controls for the sample-return container (cf

Neal, Jones, McKay) or unintentionally during partial failure of

environmental controls in more elaborate higher-cost missions.

• Low-preservation potential textures (e.g., right) will survive sample return only with sophisticated environmental controls (esp. low T).

Left: Air-dried, SEM:

Velbel

(2007), Fig. 5a. Scale marks are 10μm apart. Right: HPF/freeze-etched, FEG-SEM;

Velbel

& Barker (2008), Fig. 19. Clay in space-filling “house-of-cards”

arrangement, w/clay-coated

denticle

at bottom.

Returned clay-bearing Mars samples can tell us (things we don’t already know) about:

•

Parent materials•

Geochronology of aqueous alteration

•


•


•

Alteration conditions (T, P, pH, solute composition of former solutions, &c.)

Image credit: NASA/JPL http://www.nasa.gov/multimedia/imagegallery/image_feature_516.html

Acknowledgments•

NASA MFRP grant NNG05GL77G

•

Meteorite Working Group•

NASA

Astromaterials

Curation•

Susan J. Wentworth

•

Kathie Thomas-Keprta•

William W. Barker

•

Jean

Delvigne

(deceased)•

Ewa Danielewicz

Image credit: NASA/JPL http://www.nasa.gov/multimedia/imagegallery/image_feature_456.html

References•

Banfield, J.F. and Barker, W.W., 1994, Direct observation of reactant-product interfaces formed in natural weathering of exsolved, defective amphibole to smectite; evidence for episodic, isovolumetric reactions involving structural inheritance: Geochimica et Cosmochimica Acta, v. 58, p. 1419-1429.

•

Cole, W.F., and Lancucki, C.J., 1976, Montmorillonite pseudomorphs after amphibole from Melbourne, Australia: Clays and Clay Minerals, v. 24, p. 79-83. (Archived on at http://www.clays.org/journal/archive/volume%2024/24-2-79.pdf)

•

Delvigne, J., 1983, Micromorphology of the alteration and weathering of pyroxenes in the Koua Bocca ultramafic intrusion, Ivory Coast, West Africa: in Nahon, D., and Noack, Y., eds, Pétrologie

des Altérations

et des Sols, Volume II: Sciences Géologiques, Mémoires

(Strasbourg), vol. 72, p. 57-68.•

Delvigne, J., 1990, Hypogene and supergene alterations of orthopyroxene in the Koua Bocca ultramafic intrusion, Ivory Coast: Chemical Geology, v. 84, p. 49-53.•

Delvigne, J., 1998, Atlas of Micromorphology of Mineral Alteration and Weathering: The Canadian Mineralogist, Special Publication 3, 495 pp.•

Eggleton, R.A., 1975, Nontronite topotaxial after hedenbergite: American Mineralogist, v. 60, p. 1063-1068. (Archive online at http://www.minsocam.org/ammin/AM60/AM60_1063.pdf)

•

Eggleton R.A. and Boland J.N., 1982, Weathering of enstatite to talc through a sequence of transitional phases: Clays and Clay Minerals, v. 30, p. 11-20. (Archive online at http://www.clays.org/journal/archive/volume%2030/30-1-11.pdf)

•

Lasaga, A.C., 1984, Chemical kinetics of water-rock interactions: Journal of Geophysical Research, v. 89B, p. 4009-4025.•

Lasaga, A.C., 1998, Kinetic Theory in the Earth Sciences, Princeton, N.J., Princeton University Press, 811 p.•

McSween, H.Y., Jr., Arvidson, R.E., Bell, J.F., III, Blaney, D., Cabrol, N.A., Christensen, P.R., Clark, B.C., Crisp, J.A., Crumpler, L.S., Des Marais, D.J., Farmer, J.D., Gellert, R., Ghosh, A., Gorevan, S., Graff, T., Grant, J., Haskin, L.A., Herkenhoff, K.E., Johnson, J.R., Jolliff, B.L., Klingelhoefer, G., Knudson, A.T., McLennan, S., Milam, K.A., Moersch, J.E., Morris, R.V., Rieder, R.,. Ruff, S.W., de Souza, P.A., Jr., Squyres, S.W., Wänke, H., Wang, A., Wyatt, M.B., and Zipfel, J., 2004. Basaltic rocks analyzed by the Spirit rover in Gusev

Crater. Science, v. 305, p. 842-845.•

Squyres, S.W., Grotzinger, J.P., Arvidson, R.E., Bell, J.F., III, Calvin, W., Christensen, P.R., Clark, B.C., Crisp, J.A., Farrand, W.H., Herkenhoff, K.E., Johnson, J.R., Klingelhöffer, G., Knoll, A.H., McLennan, S.M., McSween, H.Y., Jr., Morris, R.V., Rice, J.W., Jr., Rieder, R., and Soderblom, L.A., 2004. In situ evidence for an ancient aqueous environment at Meridiani

Planum, Mars. Science, v. 306, p. 1709-1714.•

Steinmann, P., Lichtner, P.C., and Shotyk, W.,1994. Reaction path approach to mineral weathering reactions. Clays and Clay Minerals, v. 42, p. 197-206. (Archived online at http://www.clays.org/journal/archive/volume%2042/42-2-197.pdf)

•

Velbel, M.A., 1985. Hydrogeochemical constraints on mass balances in forested watersheds of the southern Appalachians. In: Drever, J.I. (editor), The Chemistry of Weathering, D. Reidel, Holland, p. 231-247.

•

Velbel, M.A., 2006. Early stages of olivine weathering in Hawai’i. Abstract, LPSC XXXVII, #1807. (published & archived online at http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1807.pdf)

•

Velbel, M.A., 2007. Surface Textures and Dissolution Processes of Heavy Minerals in the Sedimentary Cycle: Examples from Pyroxenes and Amphiboles. In Mange, M., and Wright, D., eds., Heavy Minerals in Use. Developments in Sedimentology v. 58, p. 113-150.

•

Velbel, M.A., 2008. Clay minerals in returned samples and alteration conditions on Mars. Abstract, Lunar and Planetary Institute Workshop on Ground Truth from Mars: Science Payoff from a Sample Return Missions, abstract #4019 (published & archived online at http://www.lpi.usra.edu/meetings/ msr2008/pdf/4019.pdf).

•

Velbel, M.A., 2008. Aqueous corrosion textures of olivine in Mars meteorite MIL03346. Abstract, LPSC XXXIX, #1905 (published & archived online at http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1905.pdf)

•

Velbel, M.A., and Barker, W.W., 2008. Pyroxene weathering to smectite: Conventional and low-voltage cryo-field emission scanning electron microscopy, Koua Bocca ultramafic complex, Ivory Coast. Clays and Clay Minerals, v. 56, p. 111-126.

•

Velbel, M.A., Wentworth, S.J., Thomas-Keprta, K.L., Donatelle, A.R., and McKay, D.S., 2007. Microdenticles: Aqueous corrosion textures on weathered chain silicates as terrestrial analogs of pyroxene alteration in Mars meteorites. Abstract #5172, 70th Annual Meeting of the Meteoriticial

Society, Tucson, Arizona. Meteoritics & Planetary Science, v. 42, p. A156.

•

Wentworth, S.J., Gibson, E.K., Velbel, M.A., and McKay, D.S., 2005. Antarctic Dry Valleys and Indigenous Weathering in Mars Meteorites: Implications for Water and Life on Mars. Icarus, v. 174, p. 382-395.

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