Calcium Isotopic anomalies in the Allende meteorite

Abstract

We report isotopic anomalies in Ca which were found in two Ca-Al-rich inclusions of the Allende meteorite. These inclusions previously had been shown to contain special anomalies for Mg and O which were attributed to fractionation and unknown nuclear effects. The Ca data, when corrected for mass fractionation by using ^(40)Ca/^(44)Ca as a standard show nonlinear isotopic effects in ^(48)Ca of + 13.5 per mil and in ^(42)Ca of +1.7 per mil for one sample. The second sample shows a ^(48)Ca depletion of - 2.9 per mil, but all other Isotopes are normal. Samples with large excesses in ^(26)Mg show no Ca anomalies. The effects demonstrate that isotopic anomalies exist for higher-atomic-number refractory elements in solar-system materials and do not appear to be readily explainable by a simple model. The correlation of O, Mg, and Ca results on the same inclusions requires the addition and preservation in the solar system of components from diverse nucleosynthetic sources. Observed anomalous Mg. and Ca compositions for coexisting mineral phases are uniform within each inclusion, and require initial isotopic homogeneity within an inclusion but the preservation of wide variations between inclusions. Assumming formation of these inclusions by condensation from a gaseous part of the solar nebula, this Implies Isotopic heterogeneity on a scale of 10-10^2 km within the nebula.