OXYGEN DIFFUSION IN AN FE-RICH BASALT MELT

The self-diffusion of oxygen has been measured in an FeTi basalt melt at one atmosphere from 1320-1500°C under different oxygen fugacities. Diffusivities were determined by measuring isotopic exchange between spheres of melt and flowing oxygen in a vertical tube furnace. The oxidation state of the melt was varied by performing experiments in either O2 or CO2 gas. The diffusion data for experiments in both gases can be fit to the equation D = 1.4 × 10 exp(-60(±7) × 103/RT) cm2/s. The observed self-diffusivities for oxygen in the basalt melt are one to two orders of magnitude lower than published chemical diffusivities at one atmosphere. Diffusivities in basalt melt at each temperature in O2 and CO2 gas are similar within experimental error (≤0.2 log D units at the 1 σ level) and indicate that oxygen self-diffusion is insensitive to the oxidation state of Fe in natural basalt melts. The redox independence of oxygen self-diffusion observed in this study suggests that oxygen transport in natural magmas will not be significantly affected by changes in their redox state caused by degassing and/or crystallization. © 1990.