ABSTRACT

Oxygen self-diffusion coefficients in natural titanite (sphene) single crystals were experimentally determined under hydrothermal conditions at 700° to 900°C and 100 MPa water pressure using an ion microprobe (SIMS). Oxygen self-diffusion parallel to the c-axis is described by an Arrhenius relation with pre-exponential factor D₀ = 1_–1⁺⁵ × 10^–8 m²/sec and activation energy Q = 254 ± 28 kJ/mol. Oxygen diffusion is isotropic within the measurement reproducibility of approximately a factor of 2. The relatively low diffusion coefficients for oxygen yield closure temperatures of 450° to 750°C for small crystals of titanite at typical cooling rates, which suggests that useful data on cooling rates of igneous rocks, or of metamorphic episodes, can be obtained because the size of titanite crystals in rocks is normally small.