Multiphysics of serpentinite dehydration

Water plays a fundamental role in the geodynamic processes affecting the Earth’s interior. Subduction zones are the primary locations on Earth where water is cycled between the surface and interior through the burial of the hydrated lithosphere and eventual dehydration, upwards migration, and release back to the atmosphere. Among subducted rocks, serpentinites are particularly important because they store large quantities of structurally bound water and release fluids during progressive multi-staged metamorphic dehydration reactions. These fluids influence subduction zone dynamics, arc magmatism, element cycling, and seismicity. However, considering the rocks at the depths where metamorphic dehydration reactions occur are typically impermeable, it is unclear how fluids produced through dehydration reactions escape from the subducting slab. This thesis investigates the coupled permeability and mechanical property evolution associated with serpentinite dehydration, with a particular focus on the antigorite and brucite dehydration reaction and the formation of olivine-bearing dehydration vein networks in order to quantify and gain insight on how dehydration reactions facilitate deep Earth fluid flow and the mechanical responses caused by dehydration.

The thesis begins by reviewing the geological and physical background that motivates this work. Chapter 1 introduces how the water cycle on Earth is linked to tectonics, the formation and significance of serpentinites, dehydration processes in subduction zones, and the physics of fluid flow in the deep Earth. It further presents the theoretical and computational approaches employed throughout the thesis, including material property homogenization and numerical techniques such as finite element modeling, machine learning, and graph theory.

Chapter 2 begins the main research contributions of this thesis, addressing the permeability of porous olivine aggregates (POAs) that form within dehydration veins during antigorite and brucite breakdown. Using high-resolution X-ray microtomography and GPU-accelerated finite element simulations of Stokes flow, I determined the permeability tensors of these POAs in experimentally dehydrated serpentinite samples. Representative volume element analyses demonstrate that within uncompacted dehydration veins, permeability converges at length scales several times larger than the mean olivine grain size and reaches values of approximately 10−14 − 10−13 m2 at porosities near 30%, representing a local permeability increase of up to nine orders of magnitude relative to intact serpentinite. The calculated permeability is nearly isotropic and closely follows grain-size-dependent Kozeny–Carman scaling relationships. These results show that dehydration simultaneously generates fluid and creates highly permeable drainage pathways, providing a mechanism that facilitates deep Earth fluid flow in otherwise impermeable rocks. […]