Subsolidus REE partitioning between pyroxene and plagioclase in cumulative eucrites: An ion microprobe investigation
- Univ. of New Mexico, Albuquerque, NM (United States)
- Woods Hole Oceanographic Institute, MA (United States)
In an attempt to elucidate the relationship between the cumulate eucrites and the noncumulate (main series) eucrites, we have examined the trace-element systematics of plagioclase grains that coexist with inverted pigeonites of the cumulative eucrites. Analyses were done by secondary ion mass spectrometry (SIMS). Plagioclase compositions are uniform in trace-element abundances within grains from each cumulate eucrite, but are variable between the four analyzed: Moama, Moore County, Serra de Mage, and Binda. Shapes of CI-normalized trace-element abundance patterns of the plagioclase grains of the cumulates are typical of plagioclase, showing a LREE-enriched pattern with positive Eu anomalies reflecting the site preference of Eu{sup 2+} in the feldspar structure. Using trace-element concentrations of the pyroxenes (orthopyroxene, pigeonite, augite; Pun and Papike, 1995) and plagioclase (this study), we calculate the subsolidus partition coefficients (Ds) for the REEs and Y between plagioclase and pyroxens in the examined cumulate eucrites. Trace-element systematics suggest that igneous trace-element signatures have been altered by subsolidus exchange for both the plagioclase and pyroxene. Calculated hypothetical parental-melt patterns determined form pyroxene and plagioclase are different and can differ by a factor of 4-5 for individual REEs. 36 refs., 4 figs., 4 tabs.
- OSTI ID:
- 617827
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 23 Vol. 61; ISSN 0016-7037; ISSN GCACAK
- Country of Publication:
- United States
- Language:
- English
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