Olivine zoning and retrograde olivine-orthopyroxene-metal equilibration in H5 and H6 chondrites
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CitationReisener, R. J., Goldstein, J. I., & Petaev, M. I. (2006). Olivine zoning and retrograde olivine‐orthopyroxene‐metal equilibration in H5 and H6 chondrites. Meteoritics & Planetary Science, 41(12), 1839-1852.
PublisherThe Meteoritical Society
JournalMeteoritics & Planetary Science
AbstractElectron microprobe studies of several H5 and H6 chondrites reveal that olivine crystals exhibit systematic Fe-Mg zoning near olivine-metal interfaces. Olivine Fa concentrations decrease by up to 2 mol% toward zoned taenite + kamacite particles (formed after relatively small amounts of taenite undercooling) and increase by up to 2 mol% toward zoneless plessite particles (formed after ~200 degrees C of taenite undercooling). The olivine zoning can be understood in terms of localized olivine-orthopyroxene-metal reactions during cooling from the peak metamorphic temperature. The silicate-metal reactions were influenced by solid-state metal phase transformations, and the two types of olivine zoning profiles resulted from variable amounts of taenite undercooling at temperatures <700 degrees C. The relevant silicate-metal reactions are modeled using chemical thermodynamics. Systematic olivine Fe-Mg zoning adjacent to metal is an expected consequence of retrograde silicate-metal reactions, and the presence of such zoning provides strong evidence that the silicate and metallic minerals evolved in situ during cooling from the peak metamorphic temperature.