Grain growth in an olivine-melt system: Convergence of Experiments and phase-field modeling

The application of phase-field modeling to geological systems enables a quantitative investigation of how various boundary conditions influence texture evolution. This may be used to reconstruct the timescales of non-equilibrium solidification in magmatic rocks (e.g. through the use of crystal size distributions, CSD, and diffusion chronometry). In this study, we developed a multi-component solidification model tailored for magmatic systems accommodating an unlimited number of crystals with varying orientations and anisotropies. Thermodynamic data from the MELTS database in combination with a surface anisotropy model (using surface energies from the literature) were used to model the growth of multi-faceted crystals.. Experiments as well as numerical models to study the coarsening of olivine crystals in a melt were carried out at a high constant undercooling (ΔT = 250 K at 1247 °C for annealing times of 1h, 4 h,18 h, and 72 h). Average growth rates and interface mobility in the experiments and models were consistent with each other for a coarsening behavior governed by equations of diffusion-controlled growth: d ≈ Mt^1/3, where d is an average diameter of crystals and M is a kinetic coefficient. From the kinetic coefficient an average diffusion coefficient of components can be evaluated as D ≈ 2 x 10^-10 m²/s. This value is similar to diffusivities expected for divalent cations in many basaltic melts, and somewhat faster than the diffusion rates expected for network formers such as Si.