Other
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33..603o&link_type=abstract
Meteoritics & Planetary Science, vol. 33, no. 4, pp. 603-622.
Other
19
Scientific paper
The N and C abundances and isotopic compositions of acid insoluble carbonaceous material in 13 primitive chondrites (5 UOCs, 3 CMs, 3 ECs, a CI and a CR) have been measured by stepped combustion. While the range of C isotopic compositions observed is only about d13C=30deg the N isotopes range from d15NE-40deg to 260deg After correction for metamorphism, presolar nanodiamonds appear to have made up a fairly constant 3-4wt% of the insoluble C in all the chondrites studied. The apparently similar initial presolar nanodiamond to organic C ratios, and the correlations of elemental and isotopic compositions with metamorphic indicators in the OCs and ECs, suggest that the chondrites all accreted similar organic material. This original material probably most closely resembles that now found in Renazzo and Semarkona. These two meteorites have almost M-shaped N isotope release profiles which can be most simply explained by the superposition of two components, one with a composition between d15N=-20deg and -40deg and a narrow combustion interval, the other having a broader release profile and a composition of d15NE260deg Although isotopically more subdued, the CI and 3 CMs all appear to show vestiges of this M-shaped profile. How and where the components in the acid insoluble organics formed remains poorly constrained. The small variation in nanodiamond to organic C ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30%. The most 15N-rich material probably formed in the ISM and the fraction of organic N in Renazzo in this material ranges from 40% to 70%. The isotopically light component may have formed in the Solar System but the limited range in nanodiamond to total organic C ratios in the chondrite groups is consistent with most of the organic material being presolar.
Arden John W.
Ash Richard D.
Grady Michael
O'D. Alexander Conel M.
Pillinger Colin T.
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