Measurements were made of the uptake of 44Ca from a layer of 44Ca-enriched calcite powder during the static recrystallization of a single crystal of calcite at 900C. A region about 500μm-wide, adjacent to the powder layer, was heterogeneously enriched in 44Ca, and complex zoning patterns, including sharp steps in composition and continuous increases and decreases in 44Ca content, developed. The zoning patterns were interpreted as being due to variations in the grain boundary migration rate. An analytical model was applied which permitted the product of grain-boundary diffusion coefficient and grain-boundary width (DGBδ) to be calculated from the grain boundary migration rate and the compositional gradient away from the powder layer. The value of DGBδ in the mobile grain boundaries was at least 5 orders of magnitude greater than the published value for static boundaries under the same conditions.

Fast Diffusion along Mobile Grain Boundaries in Calcite. A.McCaig, S.J.Covey-Crump, W.B.Ismaïl, G.E.Lloyd: Contributions to Mineralogy and Petrology, 2007, 153[2], 159-75