HR: 1340h
AN: V43C-1431    [Abstracts]
TI: Oxygen Isotope Variability of the Tagish Lake Meteorite
AU: * Russell, S D
EM: sdrussel@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AU: Longstaffe, F J
EM: flongsta@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AU: Larson, T E
EM: tlarson@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AU: King, P L
EM: penny.king@uwo.ca
AF: The University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AB: Triple oxygen isotope data for anhydrous phases and bulk samples provide insight into the complex history of the Tagish Lake carbonaceous chondrite meteorite. Oxygen was extracted from hand-picked separates of anhydrous phases by laser fluorination and from powdered bulk samples by conventional methods, both of which used BrF5. The oxygen isotope compositions of pyroxene and olivine concentrates ($>$95% purity) and individual chondrules describe a line (d17O = 0.974 * d18O - 3.11; R$^2$ = 0.9959) for the Tagish Lake meteorite that is very similar to the Murchison anhydrous mineral mixing line. Three possible sources of pyroxene identified in Tagish Lake include: pyroxene chondrules, disaggregated pyroxene fragments, and olivine-(pyroxene) chondrules. The oxygen isotope values of pyroxene separates (d18O = -6.2 to -4.5 permil; d17O = -9.3 to -7.3 permil) are significantly lower than those obtained for olivine (d18O = 3.1 to 5.1 permil; d17O = -0.2 to 2.2 permil). These data are interpreted to indicate that pyroxene acquired its oxygen isotopic composition under different conditions than olivine in the early solar nebula. Olivine-(pyroxene) chondrule oxygen isotope compositions (d18O = 0.8 to 4.7 permil; d17O = -3.5 to 0.8 permil) typically plot between those of olivine and pyroxene, suggestive of a two-component mixture. The triple oxygen isotope values for nine "pristine" and "degraded" bulk samples of the Tagish Lake meteorite are much higher than those obtained for pyroxene, olivine and chondrules separates. "Pristine" samples were collected immediately after the meteorite fall, whereas "degraded" material was obtained approximately 4 months later, from the ice-(water) cover on Tagish Lake. The "pristine" samples (d18O = 16.9 to 17.5 permil; d17O = 8.5 to 9.0 permil) plot close to, but below the Terrestrial Fractionation Line (TFL). "Degraded" samples also plot just below the TFL, but are more enriched in 18O and 17O (d18O = 21.2 to 23.5 permil; d17O = 10.3 to 12.2 permil) than "pristine" samples. All bulk samples follow a trend that is close to the CM meteorite mixing line, as do results for two bulk samples reported earlier by Clayton et al. (2001). The variation in oxygen isotope compositions of the bulk samples is consistent with mixing between anhydrous phases and a much more abundant, 18O and 17O-rich clay matrix, whose composition is expected to lie on or slightly above the TFL.
DE: 6215 Extraterrestrial materials
DE: 6240 Meteorites and tektites
DE: 1040 Isotopic composition/chemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting