Pegmatites (and rare metal granites) are igneous rocks with a granitic composition, characterised by crystal growth dominated texture. They are often enriched in rare elements (such as Li, Cs, Be, Nb, Ta…) and offer valuable deposit of economic interest that belong to the list of critical raw material defined by the European commission. The aim is to use modeling to understand the formation of pegmatite, and especially the parameters that control the migration distance between their sources (granite, migmatites) and their level of emplacement.

We use a two phase flow finite difference code, in Julia, based on the porosity waves with compressible fluid in compressible medium, where the porosity is interpreted as melt [1,2], to model the magma migration inside migmatitics domes. To improve the yet existing codes, we implement temperature in our two phase flow formulation, it will be calculated from energy conservation to take into account the latent heat of the partial melting and the crystallisation. It will allow the to stop the experiments upon magma crystallisation. It will also be use to increase the viscosity of the melt while it cools down.

We here present the results of a preliminary 1D version of our model (without temperature). It shows that an increase in the ratio of matrix permeability over the fluid viscosity results in a greater distance travelled by the melt, for a constant number of time step. For a fluid viscosity of 10⁴ Pa.s the increase of matrix (dynamic) permeability from 10^-13 to 10^-11 m^-2 fasten the migration of the melt of a factor 2 and the travelled distance by a factor 1. When the energy will be implemented, we will compare the impact of matrix permeability, the fluid viscosity and the geothermal gradient on the height of the magmatic migration.

References:

[1] L. Räss, T. Duretz & Y.Y. Podladchikov (2020). https://doi.org/10.1093/gji/ggz239

[2] A. Plunder & al. (2022). https://doi.org/10.1016/j.lithos.2022.106652