NanoSIMS imaging of insoluble organic matter in ordinary chondrites: Comparison with carbonaceous chondrites

The insoluble organic matter (IOM) is known to be enriched in deuterium in carbonaceous chondrites (CC) and ordinary chondrites (OC) [1]. Moreover, the isotopic composition of the IOM in CI and CM chondrites is heterogeneous at the molecular scale [2] and the micron scale [3]. In Orgueil IOM, the occurrence of D-rich hot spots is related to the heterogeneous distribution of organic radicals caracterised by a D/H ratio of 1.5% [4]. The D-isotopic enrichment is related to ion-molecule like reactions - taking place in the outer areas of the protosolar nebula or the interestellar space - that have affected the IOM before accretion on the parent body. The isotopic variations of IOMs in various types of chondrites are complex and have been related to parent body processes [1], if we assume a comon precursor to the IOM in all the parent bodies. However, this hypothesis seems inconsistent with in situ imaging of organic matter in the matrices of carbonaceous chondrites, which reveals that it exists at least two kinds of organic matter [5].