Relict Refractory Element Rich Phases in Type B CAI

Abstract

Of the possible processes involved in Type B CAI history, igneous processes are the most tractable for study. Temperature and time scales inferred are commensurate with feasible laboratory simulations. We have previously reported melilite (mel) crystal liquid partition coefficients, Di, for Sm, Yb, Sr (Eu^(++) analog), and Y (Ho analog). Our data for akermanite (Ak) 30 mel compositions is in good agreement with literature data where direct/extrapolated comparisons are possible. Even allowing for significant variations in Di with progressive crystallization, comparisons of predictions for the initial (0-30%) fractional crystallization of mel with our Sr, Y contents obtained for mel cores in Allende Type B CAI, with comparable Ak contents, indicate that the natural data substantially exceed (factors of 1.5-2.5 x) those predicted. Similar results are obtained for Y, Zr in fassaite (fass) based on estimates of the Di from literature data. In this case, excesses of these trace elements are up to factors of about x 5. Thus, while the trace elements observed in natural CAI (Sr in mel and Y, Zr in fass) are in qualitative agreement with igneous partitioning, the trace element abundances are higher than quantitative predictions.