High temperature phase equilibria in a solar-composition gas

摘要: Abstract Using recent additions to thermochemical data on minerals and information their solid solution behavior, new equilibrium phase diagrams have been computed in a system of solar gas composition (Si, Al, Mg, Ca, Fe, Ni, Ti, Na, K, C, H, O, S, N) the pressure temperature ranges 1 10 −6 bar 1153 1773 K respectively. These calculations show that Fe-Ni alloy condenses before all silicates included here (except melilite) down 2 · −4 below which plagioclase clinopyroxene condense first. Orthopyroxene next followed by ilmenite. Pressure-temperature variation chemical melilite, clinopyroxene, orthopyroxene, metal may be used for cosmothermometry cosmobarometry assemblages. The major transition from refractory oxides melilite (the meteorite ‘inclusion assemblage’) an assemblage alloy, olivine, pyroxenes (‘planet-forming’) takes place within narrow interval temperature. Small fluctuations either or across this region result drastic changes types modes minerals, explain wide mineralogical varieties meteorites.