Open AccessIsotopic composition of carbonates in the SNC meteorites, Allan Hills 84001 and Zagami
Author(s) -
Jull A. J. T.,
Eastoe C. J.,
Cloudt S.
Publication year - 1997
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/96je03111
Subject(s) - meteorite , carbonate , geology , mars exploration program , fractionation , astrobiology , chondrite , martian , mineralogy , chemistry , geochemistry , physics , organic chemistry
We have measured the 13 C/ 12 C and 14 C/ 12 C ratios in CO 2 released by acid etching of the meteorites Zagami and Allan Hills 84001. We use the 14 C as a label to identify extraterrestrial carbonate phases, as they will have a low 14 C/ 12 C ratio (< ∼ 4% modern terrestrial ratio) compared to recent terrestrial material. The new studies on Allan Hills 84001 confirm previous conclusions that the Fe, Mg‐rich carbonate grains in this meteorite contain carbon with δ 13 C as high as +45‰. In contrast, the carbon released from Zagami is depleted in 13 C with δ 13 C as low as ∼20‰. We conclude that the isotopic composition of the carbon as carbonate released from acid etching of Zagami is different from the carbonates observed in both Allan Hills 84001 and Nakhla. With the assumption that all of these meteorites sample the surface of Mars, we propose that the Zagami carbonate samples a different carbon reservoir on this planet, such as a magmatic source. With this interpretation, the high δ 13 C values of carbonate observed in Allan Hills 84001 and Nakhla can be ascribed to a fractionated source compared with the originally light carbon. A likely origin for this 13 C‐enriched component is an isotopically heavy Martian atmosphere; however, given the possibility of biological activity involving Allan Hills carbonates, we cannot exclude this as a source of the isotopic fractionation.