HR: 17:45h
AN: P14C-04    [Abstracts]
TI: The Oxygen and Hydrogen Isotope Composition of the Tagish Lake Meteorite
AU: * Russell, S D
EM: sdrussel@uwo.ca
AF: Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada
AU: Longstaffe, F J
EM: flongsta@uwo.ca
AF: Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada
AU: King, P L
EM: penny.king@uwo.ca
AF: Department of Earth Science The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B7, Canada
AB: Carbonaceous chondrites provide a record of the earliest materials formed in the Solar System. We have demonstrated previously that the oxygen isotope compositions of chondrules and isolated olivine grains from the Tagish Lake meteorite describe a line (δ¹⁷O = 0.95 * δ¹⁸O – 3.24) similar to the carbonaceous chondrite anhydrous mineral line (Russell et al., 2004; Clayton et al., 1977). Clay minerals in the Tagish Lake meteorite provide a record of the aqueous alteration of its parent body. Here we report oxygen and hydrogen isotope compositions of clay-separates (saponite) and clay-rich whole-rock samples from the Tagish Lake meteorite. The clay-separates have oxygen isotope compositions (δ¹⁸O = 15.5 to 18.0 ‰; δ¹⁷O = 9.2 to 10.2 ‰; Δ¹⁷O = 0.5 to 0.8 ‰) within the range known for CI-type meteorites. The hydrogen isotope compositions (δD= 271 to 454 ‰) of the whole-rock and clay-separate samples are enriched in D relative to CI meteorites. The temperature of formation of Tagish Lake clay minerals and carbonates has been calculated using the oxygen isotope compositions of these phases, appropriate mineral oxygen-isotope thermometry equations and two possible models for the evolution of the water isotopic composition (cooling from 325 to 125 °C versus 100 to 10 °C). The Tagish Lake meteorite contains remnants of primitive phases (chondrules, isolated olivine grains and CAIs), unlike CI meteorites. We also note that the Tagish Lake meteorite has the highest δD values presently known for CI meteorites. There may be a trend of decreasing D-enrichment in CI meteorites, with the Tagish Lake example being among the most primitive of this class, or perhaps even its precursor.
DE: 1028 Composition of meteorites (3662, 6240)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3662 Meteorite mineralogy and petrology (1028, 6240)
DE: 6240 Meteorites and tektites (1028, 3662)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting