Substitution and diffusion of Cr2+ and Cr3+ in synthetic forsterite and natural olivine at 1200-1500 degrees C and 1 bar

摘要

The diffusion and substitution mechanisms of Cr in forsterite were studied as a function of crystallographic orientation and the chemical potentials of all four components in the system MgO-SiO2-Cr-O. Oxygen fugacity (f(O2)) was varied over 15.4 log units at 1400 degrees C and was fixed at the iron-wustite equilibrium for a temperature series (1200-1500 degrees C). The valence state changes of Cr along some diffusion profiles was also investigated using X-ray absorption near edge structure spectroscopy.