Interplay Between Mechanical and Petrochemical Models on the Fluid Extraction From Subduction Zones

ABSTRACT The breakdown of hydrous minerals during subduction results in a densification of the rocks, producing volume changes that can trigger fluid pressure fluctuations and hydrofracturing. These volume changes are controlled by the Clapeyron slope of the reaction and are quantified here using a macroscopic framework that integrates a zero‐dimensional mechanical model and a one‐dimensional petrological model. A Mohr–Coulomb–based mechanical model is coupled with phase equilibrium calculations (Theriak‐Domino), oxygen isotope fractionation and trace element partitioning, using the compressed compensated Redlich–Kwong (CORK) equation of state to describe fluid properties. This model can predict fluid pressure fluctuations and brittle‐failure events from successive Gibbs free energy minimisations while accounting for tensile strength and differential stress in the mechanical model. The code is released as an open‐source Python library ThorPT. For intermediate subduction geotherms, results indicate up to 5 vol.% fluid‐filled porosity without brittle failure, consistent with findings from several geophysical studies. In basalts and serpentinites, the calculated time‐averaged permeability values show intermittent episodes of permeability exceeding 10 −19 m 2 . In serpentinite, the permeability increase can be attributed to olivine formation. In mafic rocks, episodes of increased permeability are associated with the breakdown of chlorite, amphibole and lawsonite during the transition from blueschist to eclogite. In the case of warm subduction geotherms, the model results show a strong correlation between dehydration‐driven brittle failure, fluid migration and seismicity, particularly in the mafic crust. The blueschist–eclogite transition is associated with intense brittle failure, matching geothermal and geophysical models linking this depth range to seismic double layers. Our results highlight the coupled mechanism of dehydration reaction and brittle failure as a driver of episodic fluid extraction, with broad implications for fluid–rock interaction and mass transfer in subduction zones.