Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p52b..06h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P52B-06
Mathematics
Logic
[3617] Mineralogy And Petrology / Alteration And Weathering Processes, [5410] Planetary Sciences: Solid Surface Planets / Composition, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Our analysis of near-infrared spectra of low albedo soils in the northern lowlands of Mars has revealed that they can be classified into three compositional groups: (1) relatively unaltered and high-calcium pyroxene-rich, (2) pervasively leached and glass-rich, and (3) gypsum-rich. Here we present results from spectral and morphologic studies, which together show that the diversity of soils observed from orbit and those observed in situ by the Phoenix lander can largely be explained by aqueous processes acting on high-calcium pyroxene-rich soils. Soils in Acidalia Planitia, parts of the north polar sand sea, and certain units within the north polar plateau exhibit spectral signatures consistent with an enrichment in iron-bearing glass, as well as signatures consistent with leached glass rinds, which form during acidic alteration of glass surfaces. As glass enrichment can be produced during acidic leaching of basaltic sand, we have proposed that these soils are the endproducts of widespread and pervasive acidic leaching. If these altered sands originally had a composition similar to the relatively unaltered high-calcium pyroxene-rich soils observed elsewhere in the northern lowlands, then we should also expect them to contain calcium-bearing secondary precipitates, primarily gypsum. While spectral analysis of Acidalia-type soils places an approximate upper limit on their gypsum concentration of 15-20 wt.%, our results suggest that the gypsum-rich (up to 40 wt.%) sands in the Olympia Undae region of the north polar sand sea could also be sourced from Acidalia-type materials within the north polar plateau. Although Olympia Undae gypsum concentrations appear too high to justify this hypothesis, our morphologic studies of the region suggest that the high concentrations are most likely surficial and do not represent the volumetric concentrations. By mapping the distribution of tensional surface cracks on sand dunes in HiRISE images, we have shown that the strength of gypsum absorptions correlates with the density of cracks on the dunes, which we interpret as evidence that the dune surfaces are cemented by gypsum. As chemical cementation requires dissolution and transport of salts by liquid water, we hypothesize that the gypsum precipitated out of brines, perhaps similar to the putative brines observed at the Phoenix landing site. If these brines originated from ice melt within or beneath the dunes and were transported to the surface via capillary wicking, they would have produced a surface layer enriched in gypsum, consistent with the observed distribution of gypsum on the dunes. This hypothesis explains why Olympia Undae is the only unit in the region with strong gypsum signatures, even at high resolution. These results shed new light on soils at the Phoenix landing site, as particles sourced from all of the above soil types may have been observed in Optical Microscope studies of Phoenix soils. Furthermore, the high-calcium pyroxene-rich soils that we have identified could serve as a source of calcium for the calcium carbonates identified at the landing site, which differ from the magnesium and iron carbonates that have been identified elsewhere on the planet.
Bell Jon F.
Horgan B.
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