Phase-field modeling of texture evolution in magmatic rocks

Texture formation in rocks is modeled using a quantitative phase-field model of eutectic growth with three thermodynamic phases (e.g. Diopside - Anorthite - Melt) in a quasi-binary magmatic system with unlimited quantity of crystals of different orientation and anisotropy. In nature, specific layering microstructures have been observed for which many possible explanations have been provided. Moreover, textural irregularities initially induced during nucleation, by fluctuation in crystal size or by other mechanisms continue to develop and sharpen over time. By phase-field modeling, we verify two models of igneous layering. The first mechanism is that, due to the formation of a layer with crystals of larger size, these crystals will grow faster at the expense of smaller crystals. The second mechanism is that a layer with an increasing fraction of the second phase is formed on top of the initial layer of the first phase to have crystallized. We have found that, in this case, without anisotropy of surface energies, no layering is produced. The boundary conditions and parameters of the models necessary for the formation of layers will be discussed.