Co²⁺ and Ni²⁺ diffusion in olivine determined by secondary ion mass spectrometry

Abstract

 Diffusion coefficients of Co²⁺ and Ni²⁺ in synthetic single crystal forsterite along the c-axis were determined in the temperature ranges, 700–1200 °C and 800–1300 °C, respectively. The synthesized forsterite specimens were coated with thin evaporated films of CoO and NiO on the c-surface and annealed for diffusion experiments. The short penetration distance of diffusing ions in forsterite was measured by secondary ion mass spectrometry using the depth profile method. The diffusion coefficients of Co (700–1200 °C) and Ni (800–1300 °C) are given by:

and

The observed diffusion coefficient values show good linear relationships in Arrhenius plots and the activation energy values obtained agree well with the previous values, although the diffusion coefficient values observed at the high temperature end of the experimental range deviate from the previous values. These results indicate that Co and Ni diffuse in olivine with a single mechanism within the temperature range observed, possibly with an extrinsic in nature as in the case of Mg tracer diffusion observed by Chakraborty et al. 1994 and of Fe-Mg interdiffusion by Chakraborty.