Other
Scientific paper
Nov 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991e%26psl.107..339s&link_type=abstract
Earth and Planetary Science Letters, Volume 107, Issue 2, p. 339-348.
Other
12
Scientific paper
Oxygen self diffusion rates were determined in quartz samples exchanged with 18O-enriched CO2 between 745 and 900°C and various pressures, and the diffusion profiles were measured using an ion microprobe. The activation energy (Q) and preexponential factor (D0) at P(CO2) = P(tot) = 100 bar, for diffusion parallel to the c-axis are 159 ( +/- 13) kJ/g atom and 2.10 (+0.75/ -0.55) × 10-8 cm2/s. This rate is approximately 100 times slower than that obtained from hydrothermal experiments and 100 times faster than a previous 1-bar quartz-O2 exchange experiment. The oxygen diffusion rate measured at 0.6 bar, 888°C, and at 900°C in vacuum is in agreement with the previous 1-bar exchange experiments with 18O2. The effect of higher CO2 pressures is small. At 900°C, the diffusion rate exchanged with CO2 is = 2.35 × 10-15 cm2/s at 100 bar, 2.24 × 10-15 cm2/s at 3.45 kbar and 8.13 × 10-15 cm2/s at 7.2 kbar.
There is probably a diffusing species, other than oxygen, that enhances the oxygen diffusion rate in these quartz-CO2 systems, relative to that occurring at very low pressures or in a vacuum. The effect of this diffusing species, however, is not as strong as that associated with H2O. Preserved oxygen isotope fractionations between coexisting minerals in a slowly cooled, high-grade metamorphic terrane will vary depending upon whether a water-rich phase was present or not. Closure temperatures will be approximately 100°C higher in rocks where no water-rich phase was present during cooling. The measured fractionations between coexisting minerals in metamorphic rocks may potentially be used as a sensor of water presence during retrogression.
Giletti Bruno J.
Sharp Zachary D.
Yoder Hatten S.
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