Clay Formation Dominantly in the Subsurface? Implications for Early Mars Environments

Details Clay Formation Dominantly in the Subsurface? Implications for Early Mars Environments Clay Formation Dominantly in the Subsurface? Implications for Early Mars Environments

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31d1726e&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P31D-1726

Biology

[5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Alteration minerals preserved in the ancient crust of Mars record changes in water availability, climate, and potential habitats for life during the first billion years of the planet's history. Widespread clay minerals discovered in Noachian (>~3.7 Gyr) terrains indicate long-duration alteration by neutral to high pH water; however, to date, evidence for specific environmental conditions, e.g. weathering, lacustrine, or hydrothermal clay formation, has been ambiguous. We examined mineral associations in clay-bearing terrains, considered relative ages and stratigraphic relationships of alteration mineral-bearing deposits, and evaluated models for aqueous alteration of basalt. Available data are consistent with clay mineral formation by mostly subsurface aqueous processes during the Noachian epoch. Low water:rock ratio processes in largely closed-system conditions formed Fe/Mg phyllosilicates (smectites, chlorites) from basaltic materials at temperatures ranging from ambient to 300 C. The Fe/Mg clay-bearing units formed are volumetrically large and occupy some of the deepest exposed stratigraphic units; however, their formation would have resulted in little change in the bulk chemistry of Noachian crustal rocks. In contrast to the Noachian crustal clay deposits dominated by Fe/Mg phyllosilicates with other diverse hydrated silicate phases, stratigraphically higher deposits contain clay minerals with more Al clays (kaolinite, montmorillonite), silica, and salts. These appear to have formed later under open-system, surface to near-surface alteration. These findings suggest that continuously warm surface conditions with stable liquid water did not need to be maintained in order to form clays during the Noachian. Instead, surface waters may have been geologically brief and the longest-lived aqueous environments on early Mars may have been in the subsurface.

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