Towards coupled modeling of grain-scale non-equilibrium thermodynamics and mantle-scale geodynamics

Abstract:

We are developing a 2D model of grain-scale chemical transport, crystal growth, and deformation starting from the framework of classical irreversible thermodynamics. Much of the non-equilibrium problem is simplified by removal of the thermodynamic forces of temperature and charge gradients, although it is also complicated by stress and strain due to mantle-scale stresses and grain-scale density changes. Our goal is to approximate the chemical evolution of a non-equilibrium mineral assemblage undergoing continuous melting and solid-state phase transformations. It is then easy to model disequilibrium chemical evolution of trace elements which naturally include complicated geometry-dependent interactions between grains, grains and liquid, and phase transformations within grains. Grain-scale models may be coupled to mantle-scale geodynamic models by having grain-scale models represent the mantle at Lagrangian points within the mantle-scale model. All bulk geophysical properties, mineralogy, anisotropy, and geochemical budgets can be evaluated at the grain scale in a non-equilibrium framework for a given point in a mantle-scale model. Robustness of the coupled model depends primarily on the treatment of open-system melt advection, the number and distribution of grain-scale models, and interpolation schemes.