Martian meteorites and Martian magnetic anomalies: A new perspective from NWA 7034

We present the magnetic properties of the Noachian Martian breccia NWA 7034. Among the 25 unpaired Martian meteorites studied to date, NWA 7034 has a unique magnetic mineralogy. It contains about 15 wt % of iron oxides as magnetite that has experienced cation substitution and partial alteration to maghemite, with about a quarter of the oxides being pure maghemite. It also contains oxyhydroxides in the form of superparamagnetic goethite. The presence of maghemite and goethite makes NWA 7034 the most oxidized Martian meteorite. The overall magnetic assemblage is partly linked to near-surface hydrothermal alteration. The high concentration of magnetic phases with high laboratory unblocking temperatures makes NWA 7034 a plausible analogue source lithology for the strong magnetization of the Martian Noachian crust. Near-surface hydrothermal alteration can enhance the remanence of Martian rocks and account for local, high magnetic anomalies of shallow source.