Coupling of shear banding and dehydration in serpentinite: a numerical study

Serpentinites are hydrous rocks with a wide pressure-temperature stability field that play a key role in geodynamic settings such as subduction zones and associated seismic regions, and strongly influence the deep-water cycle. Field observations and laboratory experiments indicate that dehydration of serpentinites may be caused locally due to deformation, or conversely that dehydration may induce deformation. However, the mechanical-chemical coupling between serpentinite dehydration and deformation remains poorly constrained.

Metamorphic olivine veins observed in antigorite serpentinites are interpreted as dehydration bands, and similar structures have been reproduced in laboratory experiments under uniaxial shortening and differential stress. These observations raise fundamental questions about the role of deformation in controlling serpentinite dehydration, its influence on reaction kinetics, and the impact of shear bands on fluid transport pathways. In addition to laboratory studies, numerical modelling provides a powerful approach to address these questions and to investigate dehydration processes in deforming serpentinites. However, the numerical coupling of dehydration reactions, fluid flow, and rock deformation remains challenging.

Here, we present a mathematical framework that couples poromechanical deformation, Darcy flow and a thermodynamic model for serpentinite dehydration. Based on this framework, we develop a two-dimensional numerical model using finite-difference discretization and an accelerated pseudo-transient solution method based on an iterative, matrix-free approach. The model simulates dehydration reactions driven by deformation-induced pressure variations in mechanically heterogeneous rocks. We benchmark the numerical algorithm by comparing fluid and total pressure variations around mechanically weak inclusions with results from alternative numerical methods, and by validating numerically-modelled reaction-front propagation against a new analytical solution. We then aim to investigate the relationship between shear band formation and serpentinite dehydration. Shear bands are generated using a nonlinear viscous flow law, a pressure-insensitive von Mises criterion, or a pressure-sensitive Drucker–Prager criterion. Our primary objective is to assess whether shear band-related pressure variations can localize dehydration reactions and promote the formation of fluid pathways. Finally, we incorporate a simplified reaction-kinetics model to explore the potential impact of localized deformation within shear bands on the development of dehydration bands.