Anomalous REE patterns in unequilibrated enstatite chondrites: Evidence and implications

Details Anomalous REE patterns in unequilibrated enstatite chondrites: Evidence and implications Anomalous REE patterns in unequilibrated enstatite chondrites: Evidence and implications

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24..357c&link_type=abstract

In Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F p 357-358 (SEE N94-12015 01-91)

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Carbonaceous Chondrites, Enstatite, Glass, Metamorphism (Geology), Planetary Nebulae, Rare Earth Elements, Calcium Phosphates, Oxidation, Refractory Materials, Rocks, Sulfides

Scientific paper

We present here a study of Rare Earth Element (REE) microdistributions in unequilibrated enstatite chondrites (EOC's). Although the whole rock REE contents are similar in both unequilibrated and equilibrated chondrites, the host minerals of these refractory elements are different. In the least equilibrated ordinary chondrites (UOC's), the REE reside mainly in glass whereas, in their more equilibrated counterparts, the bulk of the REE is in calcium phosphate, a metamorphic mineral that formed by oxidation of phosphorous originally contained in metal. In the smaller group of enstatite (E) chondrites, calcium phosphate is absent and the phase that contains the highest REE concentrations is a minor mineral, CaS (oldhamite), which contains approximately 50 percent of the total Ca present. In E chondrites, elements typically considered to be lithophiles (such as Ca and Mn) occur in sulfides rather than silicates. This indicates formation under extremely reducing conditions, thus in a region of the solar nebula distinct from those that supplied the more abundant ordinary and carbonaceous chondrites. Previously, we observed a variety of REE patterns in the oldhamite of UEC's; they range from almost flat to some with pronounced positive Eu and Yb anomalies. Here, we searched for complementary REE patterns in other minerals from E chondrites and found them in the major mineral, enstatite. Whenever Eu and Yb anomalies are present in this mineral, they are always negative.

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