Analysis of a spectrally unique deposit in the dissected Noachian terrain of Mars

We have analyzed a spectrally anomalous dark intracrater deposit and an adjacent lighter-toned fan-shaped deposit in the dissected Noachian terrain of Mars using a combination of high spatial and spectral resolution remote sensing data sets. The spatial proximity of these two deposits and their dust-free spectral character make these prime targets for (1) determining whether the dark-toned deposit is derived from the fan-shaped deposit and (2) constraining the nature and mineralogy of the fan-shaped deposit. Stereo observations and derived digital elevation models of the of the fan-shaped deposit show a set of three flows lobes. Calculations of the yield strength, based on morphometry of the lobes, indicate yield strengths consistent with those of other volcanic flows on Mars, although an aqueous origin cannot be discounted. The dark deposit consists of a mantle that forms dunes at its thickest portions and extends as a thinner veneer. We find no obvious morphologic association between the dark deposit and adjacent fan. Multispectral imaging from the THEMIS VIS and IR instruments show that the two deposits have different spectral characteristics, probably caused by differences in their mineralogy rather than their physical properties. Finally, modeling of MGS/TES spectra of the combined deposits indicates a feldspar-rich composition that is possibly complemented by smaller quantities of alteration products such as carbonates, and possibly sulfates and clays. These results indicate that (1) there is no association between these deposits and (2) the combined deposits have a primarily igneous mineralogy, although some aqueous alteration may have occurred.