NITROGEN ISOTOPIC SIGNATURES IN THE ACAPULCO METEORITE

We report N isotopic abundances in a bulk sample of the unique meteorite Acapulco. Although the mineral chemistry indicates a high degree of recrystallization under redox conditions intermediate between those of H and E chondrites (Palme ct al., 1981), the presence of two distinct N isotopic signatures shows that the carriers of these N components were not equilibrated. In stepwise pyrolysis, the larger (65%) N component is released mostly below 1000-degrees-C and reveals a signature of deltaN-15 = 8.9 +/- 1.2 parts per thousand which is within the range observed in chondrites. A second ''light'' component appears above 1000-degrees-C and has a signature of deltaN-15 less-than-or-equal-to - 110.5 +/- 4.0 parts per thousand (uncorrected for spallation N-15). This ''light'' N is outside the range observed in other bulk meteorites. The O isotopic composition of Acapulco (Mayeda and Clayton, 1980) is inconsistent with an origin from either the H- or E-chondrite parent bodies, and the ''light'' N component supports this.