Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios

Details Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31d1723c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P31D-1723

Biology

[1060] Geochemistry / Planetary Geochemistry, [3610] Mineralogy And Petrology / Geochemical Modeling, [5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Phyllosilicates have been detected on Mars in a wide array of geological settings. The observed phyllosilicate deposits may have formed from in situ weathering, ash alteration, sediment transport, and pedogenesis. Major occurrences of Fe/Mg smectites are observed in most phyllosilicate-bearing settings; these are sometimes associated with chrorite and serpentine. Al-rich clays, including kaolinite and montmorillonite, as well as nontronite are seen in lesser occurrences; if present they are often observed near the top of stratified units. These varied phyllosilicate deposits suggest a number of distinct geochemical processes have shaped the Martian surface and upper crust. Hydrothermal alteration, oxidative weathering, oxidative low-temperature alteration, and subaerial acidic weathering are all plausible processes for producing a subset of the observed phyllosilicates. Thermodynamic and related mass balance considerations provide insight into the conditions under which these phyllosilicates may have formed. Basalt weathering and alteration without substantial leaching is predicted to generate smectites, primary Mg- and Fe(II)-saponites, chlorite, and serpentine at ambient to hydrothermal temperatures. The relative amount of chlorite and serpentine to smectite is higher under hydrothermal conditions compared to low-temperature weathering. The carbon dioxide content of the initial fluid phase does not substantially affect the mineralogy of the weathering or alteration product except under conditions where high carbon dioxide fugacities are maintained, such as during subaerial weathering or alteration by carbon dioxide-rich hydrothermal fluids associated with magmatic systems. Substantial leaching by acidic meteoric fluids under anoxic conditions will generate Al-phyllosilicates and fluids enriched in Mg and Fe(II). Similar leaching under weakly oxic conditions will oxidize Fe(II) and produce nontronite and iron oxides along with Al-phyllosilicates. Clay assemblages composed of Mg- and Fe(II)-saponites, as produced from anoxic alteration or weathering of mafic rocks, generate a mixture of nontronite, montmorillonite, and kaolinite upon exposure to oxidizing conditions. These calculations demonstrate that there are multiple scenarios under which the observed phyllosilicate assemblages may have formed on Mars. Basalt alteration by both hydrothermal and meteoric fluids will produce similar phyllosilicates in closed systems with the same degree of leaching provided that anoxic conditions are maintained. These similarities are generally not observed in Earth analogue sites as terrestrial basalt weathering involves a substantial oxidative component. The abundance of atmospheric oxygen on Earth suggests that terrestrial analogue sites will not reflect near-surface weathering processes that may have occurred on Mars during the Noachian. Similarly, both oxidative weathering of basalt and oxidative alteration of Mg- and Fe(II)-rich phyllosilicates may produce assemblages of nontronite and Al-phyllosilicates. These assemblages may thus reflect later alteration of precursor phyllosilicates rather than changes in primary weathering or alteration processes.

Affiliated with

Also associated with

No associations

Rating

Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermodynamic Predictions of Phyllosilicate Assemblages Produced under Mars-Relevant Weathering and Alteration Scenarios will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-870308