Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla

Details Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..311j&link_type=abstract

Meteoritics, vol. 30, p. 311 (1995).

Physics

42

Scientific paper

We have measured the 13C/12C and 14C/12C ratios in CO2 released by acid etching of the carbonate-bearing SNC meteorites Allan Hills 84001 and Nakhla. Most of the C released is strongly enriched in 13C. In 10 out of 12 samples, 15‰ < δ13C < 55‰. Terrestrial values of carbonate δ13C from weathering products are generally between -10 and +10‰. Two leachate samples especially rich in 13C, ALH 84001,27 and Nakhla 25, have elemental Si/Mg ratios much lower than those of the bulk meteorites and 14C activities that are much lower than the values expected for terrestrial carbonates. The former observation indicates that these leachates consist primarily of carbonates and, less likely, phosphates. The latter observation implies that heavy C was introduced not by terrestrial weathering but by extraterrestrial processes. For ALH 84001,121 (sample 27) and Nakhla (BM 1913,26) δ13C = +41‰ and +35‰, respectively. The measured 18O/16O ratios in the leaches are similar: P δ18O ˜ 15±5‰ contrasting with 4.2%o in the bulk silicates. We infer that the C in the carbonates retains an extraterrestrial isotopic signature, but probably not O, due to its ease of isotopic exchange (Cole and Ohmoto, 1986).

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