Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..479j&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 479
Other
5
Chemical Composition, Meteoritic Composition, Radioactive Isotopes, Weathering, Carbonates, Leaching, Petrography
Scientific paper
We report the isotopic composition of carbonates present in small amounts in the SNC meteorites. Possible nonterrestrial weathering products were studied Carr et al, who observed heavy C in CO2 produced by phosphoric acid etching of Nakhla. Weathering products known as 'white druse' deposits were observed in the shergottite EETA 79001. Mittlefehldt reported the occurrence of inclusions of an Fe-Mg carbonate in the SNC orthopyroxenite ALH 84001. The petrography of these unique features suggested an extraterrestrial origin for these carbonates. These carbonates were studied to determine if they carry an isotopic record of some preterrestrial atmospheric CO2 and H2O. Previously, we have studied C-14 and stable-isotope compositions of carbonates from EETA 79001, and concluded that they were either terrestrial or had exchanged with terrestrial CO2. These samples contained 68-95% modern terrestrial C-14. We have measured the C-14 terrestrial age of EETA 79001 to be approximately 12,000 yr, and ALH 84001 approximately 13,000 yr. Carbonates irradiated in space at this time in a small meteorite would currently have about 1% of the modern terrestrial value. Samples of CO2 evolved from acid-etching experiments of SNC carbonates showed varying values for delta C-13 and delta O-18, and amounts of C-14. Three separate experiments were performed on samples of ALH 84001. We are also studying the composition of the carbonate leachates for elemental composition and other cosmogenic nuclides.
Burkland Michael Kennedy
Donahue Douglas J.
Eastoe Christopher J.
Herzog Gregory F.
Swindle Timothy D.
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