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

The coupled multicomponent diffusion of the species CaSiO, CaAlSiO and MgSiO was determined in diopside crystals in the diopside/anorthite (Di/An) system at temperatures () of 1110-1260 °C and oxygen fugacities ( ) 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 () to the measured concentration profiles. The full diffusion matrix D can be recovered by using the formula resulting in the following equation: The eigenvalues ( and ) represent upper limit values and are described by the following Arrhenius-type equations: where 1 and 2 are the first and second eigenvalue of the diffusion matrix in m s is the gas constant and is the temperature in . The dominant eigenvalue () is one quarter order of magnitude larger than the second eigenvalue (2). The eigenvectors are constant for all experiments inferring that the entire D matrix can be described with the eigenvalues as the only -dependent parameter. Additionally, the derived diffusion data and modeling approach were applied to constrain the duration of magmatic processes recorded in zoned clinopyroxene (cpx) phenocrysts from a basaltic, post-plutonic dyke of the Tertiary Adamello batholiths (N-Italy). The results reveal residence times of the overgrown cpx prior to final emplacement in the range of 0.25-1.7 years (lower limit values) testifying that the data and method can be applied to model cpx diffusion profiles in complex natural cpx.