Nitrogen-isotopic compositions of IIIE iron meteorites

The (compositionally) closely related iron meteorite groups IIIE and IIIAB were originally separated based on differences in kamacite bandwidth, the p resence of carbides only in the IIIE group, and marginally resolvable diffe rences on the Ga-Ni and Ge-Ni diagrams. A total of six IIIE iron meteorites have been analyzed for C and N using secondary ion mass spectrometry, and three of these have also been analyzed for N, Ne, and Ar by stepped combust ion. We show that these groups cannot be resolved on the basis of N abundances o r isotopic compositions but that they are marginally different in C-isotopi c composition and nitride occurrence. Cosmic-ray exposure age distributions of the IIIE and IIIAB iron meteorites seem to be significantly different. There is a significant N-isotopic range among the IIIE iron meteorites. A n egative correlation between delta(15)N and N concentration suggests that th e increase in delta(15)N resulted from diffusional loss of N.