Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53b1447f&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53B-1447
Mathematics
Logic
5460 Physical Properties Of Materials, 5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Al-OH and (Mg)Fe-OH absorptions attributable to phyllosilicate minerals have been observed in OMEGA and CRISM imaging spectrometer data from the Mawrth Vallis region of Mars. These deposits have been characterized in terms of their mineralogy and textural characteristics; however, the origin of these deposits is still very much a mystery. Here we consider possible origin hypotheses for these materials. A lithostratigraphic sequence has been determined for the light-toned Mawrth Vallis strata based on their reflectance characteristics. A basal layer of nontronite and/or (Fe)Mg bearing smectites is surmounted by materials with less well defined absorption bands. An absorption near 2.3 microns and a broad band centered near 1 micron in these layers suggest the presence of ferrous iron bearing phyllosilicates. These materials are surmounted by materials with different forms of 2.2 micron absorptions. Depending on where they occur in the sequence and where they occur laterally there are spectra more characteristic of montmorillonite, other materials with a broad 2.2 micron band which have been interpreted as hydrated silica, but which we suggest might be consistent with a kaolinite-smectite mixture, and other materials with a doublet at 2.2 microns consistent with kaolinite or dickite. These layers also have associated fracture patterns unique to the layers. Hypotheses for the nature of the fracture patterns have generally centered on hypotheses such as the desiccation of wet fine grained sediments (clays/silts) and/or the mechanism of ground ice contraction and expansion. Given that the Mawrth Vallis layered materials apparently were buried and are currently being uncovered, we suggest that the fractures might be the result of tectonic stresses imposed by an overburden. Terrestrial sedimentary rocks display different fracture patterns based on their different rheologic character which is in turn dictated by composition. An intriguing analogy might be that of layer-unique fracture patterns revealed from seismic surveys of smectite-rich mudstones (derived from a volcanic ash protolith) and overlying coarser-grained sediments in the North Sea. In the North Sea basin, fracture patterns, display several endmember fracture patterns including rectilinear, curved, and irregular. Similar patterns are observed in HiRISE images of Mawrth Vallis surfaces. Also, in the North Sea basin deposits, the fine-grained and fractured smectite-rich beds are overlain by coarser-grained (and mostly non- fractured) kaolinite, illite, and chlorite rich beds. It has been suggested that the Al-bearing phyllosilicate layers at Mawrth Vallis are draped over pre-existing topography so the North Sea analogy might be imperfect, but it shows how analysis of fracture patterns in association with lithology might provide insight into the origin of the Mawrth Vallis deposits.
Farrand William H.
Glotch Timothy D.
Rice James W. Jr.
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