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Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla
Author(s) -
Jull A. J. T.,
Eastoe C. J.,
Xue S.,
Herzog G. F.
Publication year - 1995
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1995.tb01129.x
Subject(s) - meteorite , carbonate , weathering , geology , chemistry , mineralogy , chondrite , chemical composition , isotopic signature , astrobiology , geochemistry , radiochemistry , environmental chemistry , stable isotope ratio , physics , organic chemistry , quantum mechanics
— We have measured the 13 C/ 12 C and 14 C/ 12 C ratios in CO 2 released by acid etching of the carbonate‐bearing SNC meteorites Allan Hills 84001 and Nakhla. Most of the C released is strongly enriched in 13 C. In 10 out of 12 samples, 15‰ <δ 13 C < 55‰. Terrestrial values of carbonateδ 13 C from weathering products are generally between −10 and +10‰. Two leachate samples especially rich in 13 C, ALH 84001,27 and Nakhla 25, have elemental Si/Mg ratios much lower than those of the bulk meteorites and 14 C 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) δ 13 C = +41‰ and +35‰, respectively. The measured 18 O/ 16 O ratios in the leaches are similar: δ 18 O ∼ 15 ± 5‰, contrasting with 4.2‰ 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).