2D Hydro-Mechanical-Chemical modelling of (de)hydration reactions in
deforming heterogeneous rock: The periclase-brucite model reaction
Deformation at tectonic plate boundaries involves coupling between rock
deformation, fluid flow and metamorphic reactions, but quantifying this
coupling is still elusive. We present a new two-dimensional
hydro-mechanical-chemical numerical model and investigate the coupling
between heterogeneous rock deformation and metamorphic (de)hydration
reactions. Rock deformation consists of linear viscous compressible and
power-law viscous shear deformation. Fluid flow follows Darcys law with
a Kozeny-Carman type permeability. We consider a closed isothermal
system and the reversible (de)hydration reaction: periclase and water
yields brucite. In the models, fluid pressure within a circular or
elliptical inclusion is initially below the periclase-brucite reaction
pressure, and above in the surrounding. Inclusions exhibit a shear
viscosity thousand times smaller than for the surrounding, because we
assume that periclase-water and brucite regions have different effective
viscosities. In models with circular inclusions, solid deformation has a
minor impact on the evolution of fluid pressure, porosity and reaction
front. Models with elliptical inclusions and far-field shortening
generate higher rock pressure inside the inclusion compared to circular
inclusions, and show a faster reaction-front propagation. The
propagating reaction-front increases the inclusion surface and causes an
effective, reaction-induced weakening of the heterogeneous rock.
Weakening evolves strongly nonlinear with progressive strain.
Distributions of fluid and rock pressure as well as magnitudes and
directions of fluid and solid velocities are significantly different.
The models mimic basic features of shear zones and plate boundaries and
suggest a strong impact of heterogeneous rock deformation on
(de)hydration reactions and associated reaction-induced weakening. The
applied MATLAB algorithm is provided.