Oxygen self-diffusion along high diffusivity paths in forsterite

Abstract

Diffusion profiles of ¹⁸O tracer in single crystals of forsterite following anneals at 1100° and 1200°C have been determined by a depth profiling technique using secondary ion mass spectrometry. The diffusion penetration profiles showed error function forms with developed tails. The profiles were analyzed in terms of diffusion in the forsterite lattice together with a contribution from dislocation. The present results of lattice diffusion lie in the range of the extrapolation of lines on Arrhenius plots reported previously for intracrystalline diffusion in forsterite. The dislocation diffusion coefficients are about 10⁴ times faster than the lattice diffusion at the same temperature. Diffusion along the dislocations takes place within a pipe with radius of about 0.1 nm surrounding the dislocation line. Based on the above results, O diffusion along high diffusivity paths, such as dislocations and grain boundaries, play an important role on the diffusional creep in olivine under laboratory condition.