Determination of the Diffusion Coefficient of Aluminum in Orthopyroxene by High-Pressure and High-Temperature Experiments

Abstract

This study quantifies the diffusion coefficient of Al in orthopyroxene from mantle-derived peridotite under high-temperature and high-pressure conditions. Due to Al's slow diffusion, preserved concentration gradients can retain the thermal history of the mantle. Orthopyroxene, being widespread, serves as a suitable host for such records. Unlike prior estimates based on inverse modeling, which are prone to uncertainty, this study used piston-cylinder diffusion experiments to directly measure Al diffusion from compositional profiles. The derived diffusion coefficient ranges from 10^-19 to 10^-20 m^2/s. The diffusion profile shape and co-diffusion patterns suggest that Al migrates mainly via a substitutional mechanism consistent with the Tschermak exchange.