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Partitioning of Rare Earth Elements Between Hibonite and Melt and Implications for Nebular Condensation of the Rare Earth Elements
Author(s) -
Drake Michael J.,
Boynton William V.
Publication year - 1988
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1988.tb00898.x
Subject(s) - mineral redox buffer , rare earth element , diopside , trace element , partition coefficient , chemistry , mineralogy , silicate , volatiles , rare earth , dissolution , condensation , analytical chemistry (journal) , oxygen , geology , thermodynamics , physics , environmental chemistry , organic chemistry , chromatography
— The partitioning of the rare earth elements (REE) between hibonite and silicate melt has been investigated at 1470 °C in the system calcium tschermak's molecule‐diopside. Oxygen fugacity was varied between air and the iron‐wustite buffer using conventional gas mixing, and to “infinitely reducing” using Sr 2+ as a surrogate for Eu 2+ . The partition coefficient (D) pattern is light REE enriched with D(La) = 7.15 and D(Yb) = 0.1. D(Eu) varied from about 2 in air to about 0.55 in an “infinitely reducing” atmosphere. Experiments were reversed for Eu and, by implication, a close approach to equilibrium was achieved for other elements. Absolute activity coefficients for REE in hibonite were estimated, yielding γ La = 330, γ Eu 3+ = 1200, and γ Yb = 24 000. These results suggest that unless the principal phase(s) into which a trace element is dissolving and the activity—composition relationships for that trace element in that phase(s) are known, condensation temperatures based on assumed ideal solution behavior will generally be in error.