NITROGEN ISOTOPIC COMPOSITIONS OF IRON-METEORITES

Iron meteorites analyzed in this study have nitrogen concentrations less-than-or-equal-to 70 mug/g and deltaN-15 from -90 to +150 parts per thousand. Although the iron meteorites have a large range of deltaN-15. most have values more negative than -50 parts per thousand. The nitrogen isotopic compositions were established by cosmochemical processes and were little modified by fractional crystallization or other chemical processes within the parent bodies. The data do not suggest the existence of a well-mixed solar nebular reservoir for nitrogen, as was already inferred from data from stony meteorites. The range of > 1100 parts per thousand observed for deltaN-15 in bulk meteorites is probably too large to be accounted for by physical and chemical mass-dependent fractionation processes in the solar nebula, and thus reflects nebular inhomogeneities of nucleosynthetic origin. Nitrogen isotopes may serve as fingerprints for different reservoirs, preserved in various parent bodies, in a manner similar to that observed for oxygen isotopes in stony meteorites, and oxygen-bearing phases of stony irons.