First Low-Iron Materials on Mars and Possibility of a Major Montmorillonite Component

Details First Low-Iron Materials on Mars and Possibility of a Major Montmorillonite Component First Low-Iron Materials on Mars and Possibility of a Major Montmorillonite Component

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p12a..04c&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P12A-04

Mathematics

Logic

3610 Geochemical Modeling (1009, 8410), 3672 Planetary Mineralogy And Petrology (5410), 5410 Composition (1060, 3672), 5415 Erosion And Weathering, 6225 Mars

Scientific paper

During exploration of Columbia Hills at Gusev crater, the Spirit rover of the MER mission has discovered several separate occurrences of material with a unique elemental signature. As measured by x-ray fluorescence emission using the APXS instrument, these samples stand out for their low Fe content, accompanied by corresponding increases in Al and Si but without high concentrations of mineralogically important cations such as Ca, Mg, Na, or K. No previous martian samples, from five landed missions and numerous martian meteorites, have such low iron content. Chemical trends implicate Mg sulfates and Ca phosphates are important but minor accessory minerals. Moessbauer analysis indicates some or all Ti to be present as ilmenite. The remaining component has high Al and Si abundances in proportions within the range of classical montmorillonite compositions found at various locations on Earth, including their correspondingly low concentrations of major cations. Typically the result of weathering of basaltic ash and often associated with more arid environments, the formation of montmorillonite or its alteration-product precursor implies that significant aqueous activity to facilitate geochemical separations occurred. In addition, various of these samples contain trace element anomalies that are unique for martian materials, including enrichments in Cu, Ni, Y, Ga, Cr, and possibly Pb, Co, Sr, and Zn. Adsorption by high cation exchange minerals such as montmorillonite clays or other alteration materials (allophane, silica, imogolite) often bear similar fingerprints due to their high-area charged surfaces which confer affinities for multivalent metal ions in solution. Samples of this "Independence Class" of materials have been found at three separated sites in the upper portion of Husband Hill. The samples are disparate in form, including clods (or peds), an outcrop, and a "rock". Their lighter color and rugged morphology are a common feature. The latter may indicate susceptibility to fragmentation, with possible derivation from a deeper-lying layer of source material.

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