Manganese oxides in Martian meteorites Northwest Africa (NWA) 7034 and 7533OPEN ACCESS
Yang Liu, Woodward W. Fischer, Chi Ma, John R. Beckett, Oliver Tschauner, Yunbin Guan, Usha F. Lingappa, Samuel M. Webb, Vitali B. Prakapenka, Nina L. Lanza, Carl B. Agee
Icarus
Available online: 20 April 2021
„Highlights
• Martian regolith breccia NWA 7034 and 7533 contain Mn-oxides in different lithological contexts.
• Presence of Mn-rich glass with oxidized Mn in the fusion crust indicates Martian origin of the Mn-oxides
• The petrological contexts of Mn-oxides in NWA 7034 and 7533 suggest the Mn-oxides formed after pyroxene clumps and before the final lithification (~1.35 Ga) of NWA 7034 and 7533
• Together with Mn-rich materials in sedimentary rocks of different ages, oxidized Mn in NWA 7034 and 7533 implies that atmospheric O2 may be present before 1.35 Ga“
„We report the discovery of indigenous Mn-oxides in Martian regolith breccias Northwest Africa (NWA) 7034 and 7533. These Mn-oxides occur in Mn-rich regions as nanocrystals mixed with silicates, FeOOH, and possible phosphates. The Mn-rich regions contain up to 34 wt% Mn and typically display large chemical gradients on the scale of 10–20 μm. The Martian origin of Mn-oxides was established by the presence of Mn-rich glass (4.8–5.6 wt% Mn) in the fusion crust that crosscuts a Mn-oxides-bearing monzonite clast and by the absence of Mn-oxides on the environmentally exposed surfaces (exterior and fractures) of the meteorites. Manganese K-edge X-ray absorption spectrum (XAS) of the Mn-rich glass in the fusion crust indicated that this glass included high-valent Mn species. Synchrotron micro-X-ray diffraction of a Mn-rich region in a basalt clast and XAS of Mn-rich regions in three monzonite clasts indicate Mn-oxides in these regions are dominantly hollandite-structured with 67–85 mol% of the total Mn being Mn4+. The fact that Mn-rich regions are present in diverse petrological associations but are absent in the matrix of the breccias indicates that the Mn-oxides formed through surface alteration prior to the final brecciation event that assembled NWA 7034 and 7533. Thus, the age of the Mn-oxides is older than the lithification age (arguably 1.35 Ga) of NWA 7034 and 7533. Together with findings of Mn-rich phases within Noachian and Hesperian sedimentary strata in Endeavor and Gale craters, our results suggest that Mn-oxides are a common weathering product on Mars surface, suggesting aqueous environment on the Martian surface with high redox potential.“
