Oxygen diffusion studies. I. A preliminary ion microprobe investigation of oxygen diffusion in some rock-forming minerals

Abstract

AbstractThe self diffusion of oxygen has been studied in prepared natural crystals of albite, grossular garnet, quartz, and ruffle by isotope exchange with hydrothermal water enriched in 18O, and subsequent analysis by ion microprobe. Measured oxygen diffusion coefficients (D) in quartz (‖c) may be described by D = 1.08 × 10−11 exp(−31.5 kcal/RT) cm2s−1 at 600−750°C and 1 kbar water pressure. For grossular, D = 2.5 × 10−16 cm2s−1 at 1050°C and 8 kbar, and D = 4.8 × 10−17 cm2s−1 at 850 °C and 2 kbar. All ruffle crystals exhibited variable amounts of corrosion, and an approximate diffusion coefficient of D(‖c) = 3.16 × 10−15 cm2s−1 cm2s−1 was obtained at 1050 °C and 1 kbar. Oxygen diffusion coefficients in albite, perpendicular to (001) faces, have been determined as a function of pressure at 600 °C Between 0.5 and 8.0 kbar pressure no systematic variation in the results was observed and most of the data may be described by D = 4.1 (±0.5) × 10−15 cm2s−1. Slow oxygen diffusion rates in quartz and garnet suggest that these minerals should have high ‘closure temperatures’ for oxygen exchange, and may provide reliable oxygen isotope exchange geothermometers.