Abstract:
Partial melting experiments at temperatures of 950-1300 degrees C were conducted on the H6 chondrite Kernouve under reducing conditions using CO-CO2 gas mixing and graphite-buffered sealed silica tubes to examine the effect of reducing conditions during melting of starting materials that are more oxidized relative to the oxygen Fugacity conditions of the experiments. The experiments produced a range of mineralogical and compositional changes. Olivine exhibits significant reduction to compositions of Fa(2-5) at temperatures of 1300 degrees C. In contrast, orthopyroxene exhibits only slight reduction Until the highest temperatures. Chromite is sometimes consumed by intruding, sulfides. and displays increasingly magnesian compositions ranging as low its Fe/Fe + Mg of 0.1 at a constant Cr/Cr + Al ratio. The compositional changes with increasing temperature reflect a complex set of reactions. including oxidation-reduction. One application of these experiments address whether primitive achondrites could have formed from ordinary chondrite-like precursors by partial melting Under reducing conditions. While changes observed in olivine and troilite compositions might support compositions, and thermodynamic evidence against reduction during melting of primitive achondrites compositions, and thermodynamic evidence against reduction during melting of primitive achondrites (Benedix et al. 2005) firmly refute such an idea.
