Terrestrial impact melts as analogues for the hematization of Martian surface materials

Visible and near-IR reflectivity and Mossbauer data were obtained on powders of hydrothermally-altered impact melt sheets from West Clearwater Lake, Manicouagan, and Ries (Polsingen) impact structures. The data support previous interpretations that Martian bright regions spectra can be interpreted by a ferric-bearing phase that has a relatively featureless absorption edge together with some well-crystalline (bulk) hematite to account for the 860 nm hematite band. The data also show that bands at wavelengths longer than 900 nm, which are characteristic of Martian dark regions, occur when both hematite and pyroxene are present. It thus follows that hematization of Mars can be attributed, at least in part, to hydrothermal alterations of impact melt sheets. Impact heating could also form bulk-Hm from nanophase ferric oxides.