MIT Experimental Petrology Laboratory

DIFFUSION IN MANTLE MINERALS

Determining rates for solid state diffusion of trace elements in mantle minerals at temperatures and pressures, relevant for melting in the Earth's interior is the goal of this project. There is much to learn of the kinetics of element exchange between mantle minerals and silicate melts, and many fundamental studies of common mantle minerals remain to be done. Our recent work (with former student Jim Van Orman) has been concerned with the diffusion rates for the rare earth elements in the clinopyroxene and garnet. In clinopyroxene we find that the diffusion rates vary systematically with ionic radius. Diffusion for some rare earth elements is slow enough that the interior of a crystal will remain out of equilibrium with the melt that contacts the crystal for melt generation times characteristic of mid-ocean ridge basalt production. This disequilibrium effect is being used to derive the first quantitative estimates of the rates of melt extraction in the source regions of basalts.