Carbon‐silicate aggregates in the CH chondrite Pecora Escarpment 91467: A carrier of heavy nitrogen of interstellar origin

Abstract

Abstract— Scanning electron microscopy and secondary ion mass spectrometry of the unequilibrated CH chondrite Pecora Escarpment (PCA) 91467 revealed four carriers of isotopically heavy N: (1) aggregates of carbonaceous material and silicates, (2) iron‐nickel metal grains with fine Fe‐Cr sulfide inclusions, (3) Si‐rich Fe‐Ni metal associated with Fe‐sulfide and (4) hydrated areas in the matrix. N in carbon‐silicate aggregates is isotopically heavy (δ15N is as high as 2500%0), whereas the other elements are isotopically normal, suggesting interstellar origin of carbonaceous material in the aggregates. Based on isotopic and textural evidence, we suggest that the carriers (2) and (3) were formed by brief heating in the solar nebula, whereas the carrier (4) was formed in a parent‐body asteroid. The carbon‐silicate aggregates are likely to be related to interstellar graphite found in Murchison and may also be the source of heavy N in bencubbinites.