Inventory of H sub(2)O in the ancient Martian regolith from Northwest Africa 7034: The important role of Fe oxides

Water-rich Martian regolith breccia Northwest Africa (NWA) 7034 was analyzed by Fourier transform infrared spectroscopy and transmission electron microscopy to determine the inventory and phase distribution of H sub(2)O (used herein to refer to both molecular H sub(2)O and OH super(-) structural components in hydrous minerals). Hydrous Fe oxide phases (hydromaghemite and an unidentified nanocrystalline Fe-bearing oxide phase observed with hydromaghemite) and phyllosilicates (saponite) were identified as the primary mineralogic hosts for H sub(2)O with a minor contribution from Cl-rich apatite. Based on mass balance calculations and modal abundances of minerals constrained by powder X-ray diffraction and petrography, we can account for the entire 6000ppm H sub(2)O measured in bulk rock analyses of NWA 7034. This H sub(2)O is distributed evenly between hydrous Fe-rich oxides and phyllosilicates, indicating that Fe oxides could be as important as phyllosilicates for H sub(2)O storage in Martian surface material. Key Points * H sub(2)O in NWA 7034 is hosted by Fe oxyhydroxides, phyllosilicates, and phosphates * H sub(2)O is evenly distributed between hydrous Fe oxides and phyllosilicates * Fe oxide/hydroxides could be important hosts for water on the Martian surface