A nitrogen isotope study of bencubbinites

Nitrogen-isotopic compositions of the bencubbinites-Bencubbin, Hammadah al Hamra (HH) 237, and Queen Alexandra Range (QUE) 94411-and in a petrographic ally similar chondrite Grosvenor Mountains (GRO) 95551 were measured by ste pped-combustion static mass spectrometry. Hammadah al Hamra 237 and QUE 944 11 contain isotopically heavy N, but not as heavy as that in Bencubbin or W eatherford. Grosvenor Mountains 95551 contains isotopically near-normal N a nd light N and, hence, it is not related to the bencubbinites, which is als o indicated by its O-isotopic composition. The N carriers in these meteorit es were investigated using secondary ion mass spectrometry. In the bencubbi nites, N is mostly located around sulfide in metal clasts and in impact-mel t areas. The N carriers in the former are taenite, carbide, or both; wherea s those in the latter are molten metal, tiny graphitic carbon in metal, oxi -nitride glass, or both. In the various N carriers, N is isotopically equil ibrated, and therefore the carriers are not pristine presolar grains. Isoto pically near-normal N in GRO 95551 is located in graphite. The carrier of i sotopically light N in GRO 95551 has not been found.