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Published December 1994 | metadata_only
Journal Article

Experimental study of ^(18)O/^(16)O partitioning between crystalline albite, albitic glass, and CO_2 gas


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 O'Neil and Epstein (1966) and Stolper and Epstein (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 Clayton et al. (1989) and the CO2-calcite fractionation factors determined by Chacko et al. (1991) and Rosenbaum (1994). Our results, thus, provide independent support for the high pressure calcite-mineral fractionation factors of Clayton 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 (Richet et al., 1977) differs by ~2% from that proposed by Clayton and Kieffer (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 Stolper and Epstein (1991) and imply that at equilibrium silica glass is ^(18)O-enriched relative to quartz.

Additional Information

© 1994 Elsevier Science Ltd. Received 23 January 1994. Accepted 12 July 1994. Mrs. Eleanor Dent and Drs. John Beckett, Sally Newman, and Mike Baker are thanked for valuable assistance with the technical aspects of the work. Review comments by Professors P. Richet, Y. Matsuhisa, and T. Chacko are gratefully acknowledged, as are many conversations with colleagues. The research was funded by DOE grant DE-FG03-85ER13445 and NSF grant number EAR-9303975. Participation of AM was, in part, supported by the Israel PGC fund pool. This is Division of Geological and Planetary Sciences contribution #5419. Editorial handling: B. E. Taylor.

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August 22, 2023
August 22, 2023