Numerical Simulations Reproduce Field Observations Showing Transient Weakening During Shear Zone Formation by Diffusional Hydrogen Influx and H₂O Inflow

Exposures on Holsnøy island (Bergen Arcs, Norway) indicate fluid infiltration through fractures into a dry, metastable granulite, which triggered kinetically delayed eclogitization, transient weakening during fluid-rock interaction, and formation of shear zones that widened shearing. It remains unclear whether the effects grain boundary-assisted aqueous inflow duration granulite hydration were influenced by diffusional hydrogen influx accompanying inflow. To better estimate efficiencies parameter interdependencies, 1D numerical model viscous zone is utilized validated using measured mineral phase abundance distributions H2O-contents in nominally anhydrous minerals original assemblage to constrain influx, respectively. Both hydrations are described with diffusion equation affect effective viscosity. Shear kinematics constrained observed strain thickness. The fits H2O-content profiles if diffusivity approximately one order magnitude higher than for thickness reproduced viscosity ratio between dry deforming, reequilibrating eclogite ∼104 hydrated ∼102. results suggest velocities <10−2 cm/a, diffusivities ∼10−13±1 m2/s, shearing <10 years. This study successfully links validates field data highlights importance widening eclogitization.