Calcium isotopic anomalies in the Allende meteorite

Isotopic anomalies in Ca are reported which were found in two Ca-Al-rich inclusions of the Allende meteorite. The corrected Ca data show nonlinear isotopic effects in Ca-48 of +13.5 per mil and in Ca-42 of +1.7 per mil for one sample. The second sample shows a Ca-48 depletion of -2.9 per mil, but all other isotopes are normal. Samples with large excesses in Mg-26 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. 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. Assuming formation of these inclusions by condensation from a gaseous part of the solar nebula, this implies isotopic heterogeneity on a scale of 10 to 100 km within the nebula.