However, our experiments were not conducted with the intention of extracting such information, and it is not clear how to use Eqn. 1 when marginal recrystallisation is extensive and additional shortcut pathways such as subgrain boundaries may have introduced steps into the profiles, as in the calcite aggregate experiments. Further work is planned to investigate the effects of temperature and time on the simpler single crystal profiles. However, because the geometry of grain growth is more complex than Fig. 8, and as the characteristic distance for Mn-Ca interdiffusion inferred from Fig. 7 is similar to the grain boundary migration distance, we have not attempted to extract quantitative data from this relationship. Concentration gradients and Mn penetration distances were not very sensitive to deformation state, suggesting the enhanced diffusion is an intrinsic property of the Mn-calcite solid solution.
Further work is planned to determine the oxidation state of Mn in our experiments.
Efficient takeup of Mn out of migrating grain boundaries suggests that Mn-Ca grain boundary interdiffusion is faster than volume interdiffusion, and may be an extremely rapid process in natural rocks. Systematic changes in concentration gradients as a function of temperature can be interpreted in terms of a balance between boundary migration velocity and boundary diffusion rate.