HR: 1340h
AN: P33A-1004    [Abstracts]
TI: Petrographic and isotopic ($\delta$$^{18}$O, $\delta$$^{17}$O, $\delta$$^{13}$C, and $\delta$$^{14}$C) study of carbonate minerals in a group of paired Antarctic CM2 meteorites.
AU: * Tyra, M A
EM: tyra@geol.umd.edu
AF: University of Maryland, Department of Geology and ESSIC, UMd, College Park, MD 21702 United States
AU: Farquhar, J
EM: jfarqua@essic.umd.edu
AF: University of Maryland, Department of Geology and ESSIC, UMd, College Park, MD 21702 United States
AU: Wing, B A
EM: wing@essic.umd.edu
AF: University of Maryland, Department of Geology and ESSIC, UMd, College Park, MD 21702 United States
AU: Benedix, G K
EM: gretchen22@wustl.edu
AF: Washington University of St. Louis, Department of Earth and Planetary Sciences, Washington University, Saint Louis, MO 63130 United States
AU: Jull, A
EM: jull@u.arizona.edu
AF: University of Arizona, NSF Arizona AMS Laboratory, Physics Building, University of Arizona, 1118 East Fourth St, Tucson, AZ 85721 United States
AU: Jackson, T L
EM: tjackson@ucsd.edu
AF: University of California San Diego, Department of Chemistry and Biochemistry, Stable Isotope Laboratory, University of California, La Jolla, CA 92093-0356 United States
AU: Thiemens, M H
EM: mthiemens@ucsd.edu
AF: University of California San Diego, Department of Chemistry and Biochemistry, Stable Isotope Laboratory, University of California, La Jolla, CA 92093-0356 United States
AB: Oxygen isotope data for meteoritic carbonates from CM chondrite falls have been used to gain insight into preterrestrial alteration processes and the oxygen isotopic evolution of the aqueous phase in the parent body planetesimals (e.g., Benedix et al., GCA 2003). The possibility of expanding this approach to the larger population of Antarctic meteorites represents a potentially valuable source of further information. In this study, oxygen and carbon isotopic compositions were used to evaluate terrestrial and preterrestrial carbonate formation in paired Antarctic CM2 meteorites (EET96006, EET96016, EET96017, and EET96019). The presence of microcrystalline carbonate veins consisting of intergrown magnesite and dolomite with minor calcite and well-formed, 10-50 micron diameter calcite grains in the meteorite matrix, sometimes rimmed by tocchilinite, suggests the presence of at least two generations of carbonates. $\delta$$^{18}$O and $\delta$$^{17}$O data for carbonate extracted by stepped acid extractions form an array that is bound at one end by the array of published carbonate oxygen isotope data of un-weathered CM2 falls (e.g., Benedix et al., GCA 2003) and trends toward an intersection with the terrestrial mass fractionation at $\delta$$^{18}$O and $\delta$$^{17}$O of \sim0. Carbonate $\delta$$^{13}$C and fraction of modern carbonate (FMOD$^{14}$C), when considered in the context of $\delta$$^{18}$O and $\delta$$^{17}$O, suggest the presence of at least two added terrestrial carbonate components derived during the weathering cycle: carbonate derived from atmospheric post-bomb sources and carbonate precipitated with another carbon source.
DE: 6008 Composition
DE: 6205 Asteroids and meteoroids
DE: 6240 Meteorites and tektites
DE: 1040 Isotopic composition/chemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting