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Geochemical Consequences of Widespread Clay Mineral Formation in Mars' Ancient Crust

Ehlmann, Bethany L. and Berger, Gilles and Mangold, Nicolas and Michalski, Joseph R. and Catling, David C. and Ruff, Steven W. and Chassefière, Eric and Niles, Paul B. and Chevrier, Vincent and Poulet, Francois (2013) Geochemical Consequences of Widespread Clay Mineral Formation in Mars' Ancient Crust. Space Science Reviews, 174 (1-4). pp. 329-364. ISSN 0038-6308.

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Clays form on Earth by near-surface weathering, precipitation in water bodies within basins, hydrothermal alteration (volcanic- or impact-induced), diagenesis, metamorphism, and magmatic precipitation. Diverse clay minerals have been detected from orbital investigation of terrains on Mars and are globally distributed, indicating geographically widespread aqueous alteration. Clay assemblages within deep stratigraphic units in the Martian crust include Fe/Mg smectites, chlorites and higher temperature hydrated silicates. Sedimentary clay mineral assemblages include Fe/Mg smectites, kaolinite, and sulfate, carbonate, and chloride salts. Stratigraphic sequences with multiple clay-bearing units have an upper unit with Al-clays and a lower unit with Fe/Mg-clays. The typical restriction of clay minerals to the oldest, Noachian terrains indicates a distinctive set of processes involving water-rock interaction that was prevalent early in Mars history and may have profoundly influenced the evolution of Martian geochemical systems. Current analyses of orbital data have led to the proposition of multiple clay-formation mechanisms, varying in space and time in their relative importance. These include near-surface weathering, formation in ice-dominated near-surface groundwaters, and formation by subsurface hydrothermal fluids. Near-surface, open system formation of clays would lead to fractionation of Mars’ crustal reservoir into an altered crustal reservoir and a sedimentary reservoir, potentially involving changes in the composition of Mars’ atmosphere. In contrast, formation of clays in the subsurface by either aqueous alteration or magmatic cooling would result in comparatively little geochemical fractionation or interaction of Mars’ atmospheric, crustal, and magmatic reservoirs, with the exception of long-term sequestration of water. Formation of clays within ice would have geochemical consequences intermediate between these endmembers. We outline the future analyses of orbital data, in situ measurements acquired within clay-bearing terrains, and analyses of Mars samples that are needed to more fully elucidate the mechanisms of martian clay formation and to determine the consequences for the geochemical evolution of the planet.

Item Type:Article
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URLURL TypeDescription DOIArticle
Ehlmann, Bethany L.0000-0002-2745-3240
Mangold, Nicolas0000-0002-0022-0631
Additional Information:© 2012 Springer Science+Business Media B.V. Received: 16 December 2011; Accepted: 10 August 2012; Published online: 12 September 2012. Thanks to J. Bell, J. Bishop, and M. Toplis for thorough reviews that improved this manuscript. Thanks also to M. Toplis and the ISSI conference organizers for promoting fruitful interdisciplinary discussion of clays on Mars. E. Chassefière acknowledges support from CNRS EPOV interdisciplinary program.
Funding AgencyGrant Number
CNRS EPOV Interdisciplinary ProgramUNSPECIFIED
Subject Keywords:Mars; Clay minerals; Phyllosilicates; Weathering; Alteration; Geochemistry; Mineralogy; Noachian
Issue or Number:1-4
Record Number:CaltechAUTHORS:20140224-082529148
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43938
Deposited By: Tony Diaz
Deposited On:24 Feb 2014 18:03
Last Modified:09 Mar 2020 13:19

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