Species diffusion in clinopyroxene solid solution in the diopside-anorthite system

摘要

The coupled multicomponent diffusion of the species Ca2Si2O6, CaAl2SiO6 and Mg2Si2O6 was determined in diopside crystals in the diopside/anorthite (Di/An) system at temperatures (T) of 1110-1260 degrees C and oxygen fugacities (fO(2)) between 1.0 log unit below and above the fayalite-magnetite-quartz equilibrium (FMQ +/- 1). Diffusion couples were prepared by the seed overgrowth technique. Element concentration profiles were measured perpendicular to the rim/core interface by step-scanning profiling with a field emission gun scanning electron microscope (FEG-SEM). The multicomponent diffusion matrix was solved by fitting its eigenvalues () and eigenvectors (v) to the measured concentration profiles. The full diffusion matrix D can be recovered by using the formula D=PP-1 resulting in the following equation: