Rare earth elements in chondrules from the Felix (CO3) chondrite: Comparison with Allende (CV) chondrules

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Abundances of REE, Ba, Sr, Rb, K and Ca in five chondrules and one Ca, Al-rich inclusion examined petrographically and whole rock sample from the Felix carbonaceous chondrite (CO3) were precisely determined by mass spectrometric isotope dilution techniques. The CI-chondrite normalized REE patterns for five chondrules are almost flat but show more or less anomalies of Ce, Eu and Yb. The same REE features are observed in some Allende porphyritic chondrules suggesting that one of the refractory lithophile precursors of CO and CV chondrules had an unfractionated REE pattern with minor irregularities of Ce, Eu and Yb. The coarse-grained Ca, Al-rich inclusion, which may be assigned to Type B1,exhibits a Group III REE pattern with a large negative Yb anomaly. This is inconsistent with elemental volatilities since Yb is more depleted than Eu, suggesting that a Eu-enriched component may have been added to normal Group III CAI prior to melting the inclusion precursor. The REE abundance of bulk Felix is unfractionated (1.6-1.7×CI) with ∿20% excess of Ce. Anomalies of Ce and/or Yb, commonly observed in carbonaceous chondrites, can be understood as reflecting gas/solid (or liquid) fractionation processes of chondrule precursors as well as those of Ca, Al-rich inclusions.
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