Evaluation of diffusion coefficients of Fe-Mg and Ca in olivine.

We evaluated the diffusion coefficients of Fe–Mg and Ca in olivine reported in several literatures by analyzing the diffusion profiles experimentally produced. Both the Fe and Ca contents of olivine in run products drastically increase toward the rim within a few tens of micrometers probably due to atomic diffusion from the surrounding Fe- and Ca-rich melt. The chemical zoning profiles of olivine measured with an electron microprobe were compared with those calculated by numerically solving the diffusion equation by using different diffusion coefficients. The diffusion coefficient of Fe–Mg in olivine reported by Misener (1974) gives a better fit than that by Buening and Buseck (1973), that is, the latter is too large. The diffusion coefficient of CaO in olivine reported by Jurewicz and Watson (1988b) gives a better fit than that by Morioka (1981), that is, the latter is too small. Our calculations for analyzing chemical zoning on the basis of atomic diffusion successfully reproduce the curvature of a profile experimentally made by diffusional modification of initial uniform profile of olivine.