Computer Science
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.5255m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 23, pp.5255-5266
Computer Science
6
Scientific paper
Oxygen isotope partitioning between gaseous CO 2 (~ 1 bar) and crystalline albite and albitic glass has been measured at 750-950°C, using the gas-mineral exchange techniques of and (1966) and and (1991). Convergence of oxygen isotope ratios of CO 2 and avoidance of surface-correlated fractionation effects is achieved in long runs (>200 days), using relatively coarse grain sizes. Equilibrium CO 2 -crystalline albite oxygen isotope fractionation factors are: 4.74 ± 0.22 at 750°C, 3.77 ± 0.23 at 850°C and 3.36 ± 0.21 at 950°C. These values compare well with calculations based on the experimental calcite-albite data of et al. (1989) and the CO 2 -calcite fractionation factors determined by et al. (1991) and (1994). Our results, thus, provide independent support for the high pressure calcite-mineral fractionation factors of et al. (1989). An estimate of the reduced partition function ratio for albite derived from the CO 2 -albite data using the reduced partition function ratio of CO 2 ( et al., 1977) differs by ~2% from that proposed by and (1991). CO 2 -albite exchange experiments of relatively short duration give disequilibrium fractionation factors. Oxygen diffusion coefficients calculated from these experiments, however, are comparable with previous determinations of oxygen diffusion in feldspars under nominally anhydrous conditions and support the hypothesis that isotopic exchange is diffusion-controlled. Equilibrium oxygen isotope fractionation factors determined for CO 2 -albitic glass are identical within experimental uncertainty to those determined for CO 2 -crystalline albite, thus indicating that fractionation between crystalline and glassy albite is unresolvable at the 0.1 %. level. In contrast, additional measurements of oxygen partitioning between CO 2 and silica glass confirm the results of and (1991) and imply that at equilibrium silica glass is 18 O-enriched relative to quartz.
Epstein Samuel
Matthews Aaron
Palin J. M.
Stolper Edward M.
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