Manganese oxides in Martian meteorites Northwest Africa (NWA) 7034 and 7533

We report the discovery of indigenous Mn-oxides in Martian regolith breccias Northwest17 Africa (NWA) 7034 and 7533. These Mn-oxides occur in Mn-rich regions as nanocrystals mixed18 with silicates, FeOOH, and possible phosphates. The Mn-rich regions contain up to 34 wt% Mn19 and typically display large chemical gradients on the scale of 10–20 μm. The Martian origin of20 Mn-oxides was established by the presence of Mn-rich glass (4.8–5.6 wt% Mn) in the fusion crust21 that crosscuts a Mn-oxides-bearing monzonite clast and by the absence of Mn-oxides on the22 environmentally exposed surfaces (exterior and fractures) of the meteorites. Manganese K-edge23 X-ray absorption spectrum (XAS) of the Mn-rich glass in the fusion crust indicated that this glass24 included high-valent Mn species. Synchrotron micro-X-ray diffraction of a Mn-rich region in a25 basalt clast and XAS of Mn-rich regions in three monzonite clasts indicate Mn-oxides in these26 regions are dominantly hollandite-structured with 67–85 mol% of the total Mn being Mn4+. The27 fact that Mn-rich regions are present in diverse petrological associations but are absent in the28 matrix of the breccias indicates that the Mn-oxides formed through surface alteration prior to the29 final brecciation event that assembled NWA 7034 and 7533. Thus, the age of the Mn-oxides isolder than the lithification age (arguably 1.35 Ga) 30 of NWA 7034 and 7533. Together with findings31 of Mn-rich phases within Noachian and Hesperian sedimentary strata in Endeavor and Gale craters,32 our results suggest that Mn-oxides are a common weathering product on Mars surface, suggesting33 aqueous environment on the Martian surface with high redox potential.