Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13c..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13C-07
Other
[3617] Mineralogy And Petrology / Alteration And Weathering Processes, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Low-albedo sand seas and sand sheets encircle the north polar cap of Mars and extend into Acidalia Planitia. These low albedo deposits are the type locality for TES Surface Type 2 (ST2), a silica-enriched, globally distributed compositional unit identified from deconvolution of Mars Global Surveyor TES thermal infrared spectra. The nature of ST2 is not well constrained, as the high-silica component is spectrally consistent with both primary lithologies and alteration phases. We present new evidence from Mars Express OMEGA near infrared spectra of the north polar region and Acidalia Planitia that the primary high-silica component of ST2 is an amorphous silica coating. We interpret this coating as being associated with high concentrations of iron bearing glass that have not previously been detected in these regions. These high silica, glass-rich deposits are spectrally consistent with thin silica leaching rinds formed on Earth by acidic alteration of basaltic glass. We identify ST2 concentrations with amorphous silica coating spectral signatures in a variety of geomorphic settings at high northern and southern latitudes, including within craters and volcanic complexes, possibly indicating both glass-bearing impact melts and volcanics as alteration precursor materials. In the north polar region, glass-rich, amorphous silica-coated deposits are primarily found at certain exposures of the polar layered deposits, and within the Siton Undae sand sea, which occupies the deepest basin in the northern plains. Coating signatures are also found throughout the low albedo regions of Acidalia Planitia. The lack of identified volcanic edifices or extensive impact melt sheets in the north polar region or in Acidalia Planitia suggests that the widespread silica coated sands in these regions may be the end product of alteration (for example, by olivine dissolution/glass leaching) of the basaltic sand seas that have occupied these regions throughout the Amazonian.These observations suggest that acidic alteration of glass-bearing deposits has been a widespread process on Mars, especially at high latitudes. Other manifestations of this process may include the potentially silica-rich rock coatings at the Pathfinder landing site, the amorphous silica/glass/sulfate rich light-toned outcrops at Meridiani Planum, and the recent hypothesis that dark soils in some martian highland regions may be soils produced by partial dissolution of olivine-rich bedrock. In the context of these other observations, our results may indicate that chemical weathering may play a much more important role in the formation and evolution of martian soils than has been previously thought.
Bell Jon F.
Horgan B.
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