Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p22a..04w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P22A-04
Mathematics
Logic
[5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We have mapped out the distribution, identified associated hydrated units, and proposed modes of formation for crystalline, gray hematite in Capri Chasma. HiRISE and CRISM images corresponding to the highest and largest abundances of gray hematite as measured by TES were analyzed for this study. Digital Terrain Models (DTMs) derived from HiRISE stereo pairs were used in a few locations to determine stratigraphic relationships between the hematite and other geologic units. In general, we find the gray hematite correlates to dark mantles situated on low-lying plains where there are nearby sulfate outcrops. A location with one of the highest abundances of hematite is situated on plains adjacent to kieserite outcrops. The dark hematite-bearing plains have spectra with a weak 1.93 μm absorption and HiRISE images reveal small exposures of light-toned material beneath the hematite-bearing darker mantle. There are also several light-toned layered units with mineralogies that include opal, Fe/Mg-smectite, and an unidentified mineral exhibiting a 2.22/2.27 μm doublet. These units are exposed within small hills located both inside and outside the hematite-bearing plains, and are unlikely to be the source of any hematite based upon their spatial distribution. Another location with a large occurrence of gray hematite is situated along the southern wall and floor of a ~30 km diameter, 2.5 km deep impact crater on the northern edge of the interior layered deposit within Capri Chasma. Multiple units are exposed along the crater wall, including a lower layered kieserite unit, followed by a layered mix of polyhydrated sulfates (PHS) and monohydrated sulfates, a layered PHS, a thick sequence of upper kieserite generally lacking layering, and finally an upper PHS. Covering many of these units are surficial mantles, including kiesereite-bearing dunes, spectrally bland eolian material, and a dark mantle with features centered at 1.05, 1.93, and 2.4 μm, consistent with a mixture of hematite and PHS. The source of the crystalline hematite is likely grains that are weathering out of kieserite outcrops and collecting along the plains or lower slopes, presumably as soil lags. However, erosion of light-toned PHS material seen along portions of the chasma floor could also be the source of some hematite grains, particularly hematite locations that are several kms from the central interior layered deposit.
Knudson Amy T.
Lane Melissa D.
Noe Dobrea Eldar Z.
Roach Leah
Weitz Catherine M.
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