CHOS gas/fluid‐induced reduction in ureilites

• DOI: 10.1111/maps.13755
• Publication Date: 2021-10-28T13:31:03Z
• Authors: Andrew D. Langendam; Andrew G. Tomkins; Katy A. Evans; Nicholas C. Wilson; Colin M. MacRae; Natasha R. Stephen; Aaron Torpy
• Keywords: Troilite; Sulfidation; Mineral redox buffer

Abstract Ureilite meteorites contain regions of localized olivine reduction to Fe metal widely accepted have formed by redox reactions involving oxidation graphite, a process known as secondary smelting. However, the possibility that other reductants might be responsible for this has largely been ignored. Here, 17 ureilite samples are investigated assess whether, instead smelting only solid reactants, CHOS gas/fluid could caused much Features consistent with gas‐ or supercritical fluid‐driven were found abundant in all ureilites, such fracture‐focused smelting, plume‐like reaction fronts, and addition sulfur. Many these developed away from graphite. In some it is clear coincided annealing, we suggest was enhanced diffusion facilitated higher density gas fluid, rather than slow cooling, which requires elevated pressure. The C‐CO CH 4 ‐C‐H 2 O buffers modeled examine their relative potential drive reduction. This modeling showed ‐rich fluid able produce observed mineral compositions at pressures. result, coupled textures, used develop likely series reactions. We pressures, H ‐CH ‐H S‐S ‐bearing fluid‐like phase, lower an equivalent gas, infiltrate grain boundaries fine fractures. Sulfidation form troilite may acted maintain highly reduced conditions. presence hydrocarbons ureilites supports role driven gas/fluid.