In this project chemical diffusion will be investigated experimentally in silicate melts of basaltic composition. The flattened and polished ends of capsules containing dissimilar materials will be joined by a Pt sleeve and welded shut during initial heating by a thread of gold wire wrapped around the join at the top and bottom of the sleeve. Diffusion profiles will be determined after quenching the couple by longitudinal sectioning and microprobe "linescan" for all eleven major elements. The data on numerous "linescans" corresponding to various diffusion times and initial concentration profiles will be fitted to an appropriate multicomponent solution of the diffusion equation. The aim of this exercise is to extract the off-diagonal (coupling) terms of the diffusion matrix for basaltic magmas. The calibrated diffusion matrices will be used to resolve certain intriguing aspects of crystal growth in magmatic systems ( such as whether oscillatory zoning is a natural consequence of the coupling of diffusion to the crystal liquid interface and the kinetics of interface growth) and to suggest possible melt "species" predominant in basaltic systems.
