A study of low‐albedo deposits within Amazonis Planitia craters: Evidence for locally derived ultramafic to mafic materials

Abstract

We studied low‐albedo deposits in the floors of craters within the Amazonis Planitia region using infrared data from Mars Global Surveyor Thermal Emission Spectrometer (TES) and Mars Odyssey Thermal Emission Imaging System (THEMIS), high‐resolution visible images from the Mars Orbiter Camera and THEMIS, and topographic data from the Mars Orbiter Laser Altimeter. These deposits are found within subdued to sharp‐rimmed craters that impacted into thick basaltic lava flows from Olympus Mons. These lava flows flooded the region and were subsequently eroded by aeolian processes. TES spectral modeling of the low‐albedo deposits reveals a mineralogy that is dominated by mafic minerals (olivine, pyroxene) with a derived bulk chemistry that ranges from ultramafic to mafic (∼40–52 wt % SiO2) in composition. These bulk compositions are comparable to some Martian lithologies but represent some of the lowest silica contents identified on Mars. The compositional range could be produced by either primary igneous processes or subsequent alteration by aeolian processes. The spatial distribution of the compositions reveals weak to absent groupings and does not distinguish between the igneous or aeolian scenarios. In some craters, possible local sources have been identified within the crater walls, floors and interiors; local sources may be present in additional craters but obscured by dust. No regional sources were identified within a reasonable distance in terms of sand transport but may also be obscured by dust. Therefore, the low‐albedo deposits probably resulted from aeolian erosion of local intracrater basaltic materials that were subsequently redistributed within the floors of these craters.