Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p61d..10f&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P61D-10
Other
5470 Surface Materials And Properties, 6225 Mars
Scientific paper
Archean Earth Banded Iron Formation (BIF) has been suggested as a possible terrestrial analog for Early Mars (Calvin, 1998). Two types of BIF in the United States and Canada have been differentiated based on their respective origins. The Algoma type deposits in Ontario, Canada are in close proximity to ancient volcanic centers suggesting a sub-aqueous hydrothermal origin similar to modern day sea-floor spreading centers (Gross, 1983). The Lake Superior type BIF deposits in the upper peninsula of Michigan are not associated with extrusive volcanic materials and are therefore interpreted as chemical precipitates of iron-rich waters in a shallow sea (James, 1954). The Thermal Emission Spectrometer (TES) discovery of crystalline, gray hematite in sedimentary basin type deposits on Mars supports the use of Lake Superior type BIF as a terrestrial analog. The Sinus Meridiani and Aram Chaos hematite sites are not in close proximity to a volcanic center, and do not exhibit any lava flow features (Christensen, et al., 2001). The Sinus Meridiani hematite occupies a smooth unit with abrupt boundaries suggesting that it exists within a stratigraphic layer. The Aram Chaos hematite appears to be within a closed basin around which outflow channels are common suggesting an aqueous origin. In both sites, the hematite appears to be part of layered, sedimentary rock units that suggest aqueous environments (Christensen, et al., 2001). The Lake Superior type BIF occurs in four principal facies: sulfide, carbonate, silicate, and oxide (James, 1954). These facies grade into each other in the field reflecting changes in the oxidation state of the water and occur as thin laminae alternating with chert layers. The mm scale laminations of these rocks will not be evident in large- scale (3km x 6km) TES spectra. The iron-rich minerals present in each facies are possible auxiliary minerals for the low albedo hematite regions on Mars. These minerals are: pyrite in the sulfide facies, siderite in the carbonate facies, minnesotaite and stilpnomelane in the silicate facies, and magnetite and hematite in the oxide facies. A field trip to the Lake Superior type deposits in the Marquette and Gogebic iron districts of Michigan has provided a thorough rock sampling of the different facies, including several types of crystalline, gray hematite. Micaceous, specular hematite with a schistose texture is highly metamorphosed and is probably not seen on the surface of Mars. Bulk, gray crystalline hematite occurs in relatively unmetamorphosed BIF and retains its sedimentary layer nature. It also displays a microplaty texture in some samples that is most likely the result of low-grade burial metamorphism. Some of the bulk, gray crystalline hematite displays magnetic properties suggesting some mixture of magnetite and hematite. The spectra of these bulk samples may be better analogs for Mars than pure mineral phases. The spectra of these samples will be presented and compared to what TES has observed.
Calvin Wendy M.
Fallacaro Alicia
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