RARE-EARTH ELEMENT PARTITION-COEFFICIENTS FROM ENSTATITE MELT SYNTHESIS EXPERIMENTS/

Enstatite (En(80)Fs(19)Wo(01)) was synthesized from a hypersthene norm ative basaltic melt doped at the same time with La, Ce, Nd, Sm, Eu, Dy , Er, Yb, and Lu. The rare earth element concentrations were measured in both the basaltic glass by EMPA and the enstatite by SIMS. Rare ear th element concentrations in the glass were determined by electron mic roprobe analysis with uncertainties less than two percent relative. Ra re earth element concentrations in enstatite were determined by second ary ion mass spectrometry with uncertainties less than five percent re lative. The resulting rare earth element partition signature for ensta tite is similar to previous calculated and composite low-Ca pigeonite signatures, but is better defined and differs in several details. Firs t, the enstatite LREE signature is steeper than for pigeonite. Second, the signature has a negative Eu anomaly which relates to oxygen fugac ity and third, the dependence of the partition coefficients on alumina content is linked to crystal structural constraints. Copyright (C) 19 98 Elsevier Science Ltd.