Iron and Sulfur Secondary Phases as Proxies of Aqueous Alteration on Chondrite Parent Bodies

Hydrated phases encountered in meteorites are considered as clues of the earliest interactions between their primary components and water in the solar system. We ran hydrothermal experiments associated with thermochemical modeling to constrain the alteration processes, especially the reaction pathways toward hydrated phases on the parent body(ies) from which the primitive meteorites (chondrites) come from. These parent bodies first accreted rocks and ices. We focused on the early stage after ice melting at moderate temperature and low oxygen fugacity to mimic the alteration conditions present on the CM parent body. Synthetic chondritic mixtures made of olivine (Fo 90), GEMS-like material, pyrite, and alpha-iron were reacted at T = 80 degrees C for a time period of 128 days at a water-rock mass ratio of 10. Three kinds of solutions were used in order to investigate the interactions between mineral phases and H2O, NH3, or CO2 ices, respectively. According to scanning electron microscopy (SEM) observations, Raman, X-ray photoelectron spectroscopy (XPS), and X-ray characterizations, secondary phases formed were, respectively, spinel iron oxide, magnetite, magnesium silicate hydroxide, and iron sulfide in the case of saline solution and goethite, sulfur, and ferrotochilinite +/- dolomite in the case of ammonia or carbonate solution. Thermochemical calculations, validated by experiments, simulated this complex natural history. These findings help to unravel the pathways of the alteration processes in CM chondrites.