Christine Floss^a, Corentin Le Guillou^b,c, Adrian Brearley^b

^aLaboratory for Space Sciences and Physics Department, Washington University, One Brookings Drive, St. Louis, MO 63130, USA
^bDepartment of Earth and Planetary Sciences, MCS03-2040, University of New Mexico, Albuquerque, NM 87106, USA
^cInstitut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44780 Bochum, Germany

The organic matter in the primitive CR3 chondrites QUE 99177 and MET 00426 exhibits, as in other CR chondrites, N isotopic compositions characterized by large enrichments in ¹⁵N compared to solar. These enrichments are present in the matrices of these two meteorites as localized hotspots associated with C-rich grains, and larger, more diffuse regions with more modest enrichments in ¹⁵N. Occasionally depletions in ¹⁵N are also observed. FIB-TEM analysis of isotopically anomalous as well as isotopically normal C-rich grains from the matrix of MET 00426 shows that both types of grains consist of highly disordered organic matter that exhibits a variety of morphologies. There are no obvious correlations of isotopic composition with morphology, petrographic association or elemental composition. Large diffuse regions with modest ¹⁵N enrichments may be the result of fluid action that redistributed organic matter (and the associated ¹⁵N enrichments) in veins and cracks along grain boundaries. Grain formation likely occurred in a variety of environments (e.g., molecular clouds or the outer regions of the protosolar nebula) via UV photolysis of simpler precursor ices with variable isotopic compositions.

Reference
Floss C, Le Guillou C and Brearley A (in press) Coordinated NanoSIMS and FIB-TEM Analyses of Organic Matter and Associated Matrix Materials in CR3 Chondrites. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.04.023]
Copyright Elsevier

Link to Article