Sulfide-metal-oxide phase assemblages in the D'Orbigny angrite: Implications for element diffusion paths involving Fe–Ni–S–O system and redox conditions

Abstract

The Ni-bearing metals and the Fe-oxides (wüstite/magnetite) within sulfides (troilite/pentlandite) in the D'Orbigny angrites were considered for better constraining the changing Redox as well as temperature-composition conditions during their formation. Microstructures and compositions of sulfide-metal-oxide phase assemblages were characterized by scanning and transmission electron microscopy coupled with polarized optical microscopy to reveal the element diffusion path in the Fe–Ni–S–O quaternary system for their formation. The temperatures under which these reactions took place were between 900 and 600 °C. The metal-sulfide assemblage and troilite with wüstite-magnetite core-shell crystals restrict D'Orbigny's late Redox-changing conditions. Considering these temperatures together with iron-wüstite and wüstite-magnetite Redox buffers, late events in D'Orbigny took place under log(fO2) ∼ −17 to −25.