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Partial melting of H6 ordinary chondrite Kernouvé: Constraints on the effects of reducing conditions on oxidized compositions
Author(s) -
FORD Rena L.,
BENEDIX Gretchen K.,
McCOY Timothy J.,
RUSHMER Tracy
Publication year - 2008
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2008.tb00705.x
Subject(s) - achondrite , troilite , chromite , mineral redox buffer , chondrite , partial melting , olivine , ordinary chondrite , oxygen , chemistry , geology , mineralogy , geochemistry , meteorite , basalt , astrobiology , physics , organic chemistry
— Partial melting experiments at temperatures of 950–1300 °C were conducted on the H6 chondrite Kernouvé under reducing conditions using CO‐CO 2 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 °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 as 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 such an idea, differences in oxygen isotopic composition, Cr/Cr + Al in chromite, orthopyroxene compositions, and thermodynamic evidence against reduction during melting of primitive achondrites (Benedix et al. 2005) firmly refute such an idea.