2000 GSA Annual Meeting -- Reno, Nevada
2000 GSA Annual Meeting -- Reno, Nevada
Author(s): JULL, A. J. T.(a,b), G. S. BURR (a), S. E. KLANDRUD (a), C. J. EASTOE (b) and J. W. BECK (a). (a.) NSF Arizona AMS Laboratory and (b) Department of Geosciences, University of Arizona, Tucson, AZ 85721. email: jull@u.arizona.edu
Keywords: Mars, meteorites, alteration, organic compounds,
We have measured the 13C/12C and 14C/12C ratios in CO2 released by acid etching of several Martian meteorites. We can use 14C as an indicator of terrestrial alteration of carbonates and also to differentiate between extraterrestrial organic material and recent terrestrial contamination. 14C produced in space due to spallation reactions in an extraterrestrial carbonate would be only a few percent modern. One can also show that this is the case for organic material irradiated in a small object in space. For ALH84001 and Nakhla, carbonate is enriched in 13C with d13C up to +41 to 55 , respectively. Jull et al. (1995, Meteoritics, 30, 311) indicated that uptake of terrestrial 14C by carbonates in ALH84001 had occurred to some extent during the ~13ka residence time of this meteorite on the ice in Antarctica could pose some contamination problems. Measurements of CO2 released by hydrolysis from other Martian meteorites (Lafayette and Governador Valadares) also show terrestrial alteration effects. We have also studied the 14C and 13C isotopic composition of organic matter released by selective combustion in ALH 84001 and concluded that the samples contained up to 80% terrestrial contamination (Jull et al., 1998, Science, 279, 366). Recently, we have reported new 14C and 13C isotopic analyses of organic and carbonate phases in Nakhla. These experiments included studies of soluble organic phases and insoluble material. Results show most of the organic matter in Nakhla is released by 6N HCl and there appear to be two isotopically distinct sources of extraterrestrial organics with 13C of -33 and -15 and low 14C. We estimate that at least 75% of the organic material released by 6N HCl acid etching of Nakhla is extraterrestrial. We conclude that this acid-labile component is likely similar to polymeric organics observed in CM2 chondrites. The terrestrial organic contamination has approximately modern 14C values and d13C of -25 .
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