Skip to content

Fully coupled petrological/thermo-mechanical models of magmatic systems.

Boris Kaus, Nicolas Riel, Hugo Dominguez, Jacob Frasunkiewicz, Pascal Aellig, Evangelos Moulas

Abstract

Simulating the chemical evolution of magmatic systems can be done with thermodynamic equilibrium modelling, and recently developed thermodynamic melting models do quite a good job of predicting observations and reproducing experiments for a wide range of compositions. Yet, it is a significant computational challenge as some of the most recent melting models include 11 oxides along with pressure and temperature, which makes this a 13-dimensional Gibbs energy optimisation problem. We developed the parallel software package MAGEMin for this purpose. However, each point-wise thermodynamic calculation still takes 10-50 milliseconds (depending on the complexity of the system). This is too slow if one wishes to directly couple thermodynamic with dynamic simulations of the magmatic system, as those may require 1000's-100'000s of calculations per timestep. An alternative approach is to develop simplified parameterizations from the complete thermodynamic models. That, however, requires recalibration for different scenarios, and gives up some of the predictive power of the models, such as the chemistry of the stable mineral assemblage. We therefore developed a new approach in which we dynamically update a database of precomputed points that only performs new thermodynamic calculations for points that do not yet exist in the database.  This significantly reduces the computational effort and allows coupling thermodynamic simulations with thermo-mechanical simulations in a self-consistent manner.  We illustrate the power of the method with 2D/3D thermo-kinematic simulations of magmatic systems, as well as by reactive two-phase flow calculations applied to small-scale magma transfer processes in lower crustal migmatites.