Evidence for distillation in the formation of HAL and related hibonite inclusions
New Ca- and Ti-isotopic analyses of DH-H1, 7-404, and 7-971, and Mg-isotopic analyses on DH-H1 and 7-404 are reported. O-isotopic analyses of HAL, 7-404, 7-971, and a variety of other refractory inclusions from Murchison were made in order to establish the presence or absence of FUN O-isotopic systematics. A higonite-rich residue produced by the evaporation of kaersutite was analyzed for its trace-element and isotopic abundances to see if any of the characteristics of FUN hibonite inclusions can be produced by distillation in the laboratory. These data are then used to evaluate for all four inclusions the HAL-type formation models originally proposed by Allen et al. (1980) and Lee et al. (1980). The four inclusions were found to have very similar chemical and isotopic features. All are characterized by large Ce depletions and very low Mg, Ti, and V concentrations compared to other meteoritic hibonites. All four inclusions have delta(C-48) within error of -5 per mil. Ca-, Ti-, and O-isotopic compositions are fractionated with enrichments of the heavy isotopes, and the Ti-isotopic mass fractionation is inversely correlated with Ti concentration. It is concluded that the inclusions formed primarily as distillation residues in accord with the early conclusions.