We have studied eight of the spatially largest locations in Ophir and Candor chasmata that have the highest abundances of coarse-grained gray hematite, as measured by the Mars Global Surveyor Thermal Emission Spectrometer (TES). All of the eight hematite locations correspond to relatively smooth dark units that overlie or are adjacent to light-toned rock units. Linear modeling of TES spectra sampled in the eight hematite locations shows mostly mafic associations with the hematite, dominated by pyroxene and feldspar, with a lower abundance of sulfates. The spectral and morphologic similarity between the hematite-bearing units at Ophir and Candor to those at Meridiani Planum lead us to favor a similar aqueous origin for the hematite in Valles Marineris. Water that may have infiltrated the light-toned rocks by an increase in the water table or when lakes may have existed within the canyons could have resulted in the formation of hematite-rich grains in a scenario similar to that proposed for Meridiani Planum. Erosion by wind of the formerly overlying or adjacent friable light-toned rocks that contain the hematite-rich grains enabled the more resistant hematite grains to be concentrated in sufficient abundances along the surface to be detected by TES. A more limited supply of hematite grains within the light-toned rocks, inadequate winds, subsequent burial beneath dust or sand, and fewer low-lying terrains upon which the grains could form a lag deposit may explain why there are smaller exposures of hematite within Valles Marineris compared to Meridiani Planum and Aram Chaos. Copyright 2008 by the American Geophysical Union.
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