Generation of fluids during metamorphism can significantly influence the
fluid overpressure, and thus the fluid flow in metamorphic terrains.
There is currently a large focus on developing numerical reactive
transport models, and with it follows the need for analytical solutions
to ensure correct numerical implementation. In this study, we derive
both analytical and numerical solutions to reaction-induced fluid
overpressure, coupled to temperature and fluid flow out of the reacting
front. All equations are derived from basic principles of conservation
of mass, energy and momentum. We focus on contact metamorphism, where
devolatilization reactions are particularly important owing to high
thermal fluxes allowing large volumes of fluids to be rapidly generated.
The analytical solutions reveal three key factors involved in the
pressure build-up: (i) The efficiency of the devolatilizing reaction
front (pressure build-up) relative to fluid flow (pressure relaxation),
(ii) the reaction temperature relative to the available heat in the
system and (iii) the feedback of overpressure on the reaction
temperature as a function of the Clapeyron slope. Finally, we apply the
model to two geological case scenarios. In the first case, we
investigate the influence of fluid overpressure on the movement of the
reaction front and show that it can slow down significantly and may even
be terminated owing to increased effective reaction temperature. In the
second case, the model is applied to constrain the conditions for
fracturing and inferred breccia pipe formation in organic-rich shales
owing to methane generation in the contact aureole.