Phase-Field Modeling of Reaction-Driven Cracking: Determining Conditions for Extensive Olivine Serpentinization

Abstract

The motion of plates leads to cycling of chemically bound water and volatiles through the Earth's interior, having consequences for arc magmatism and seismic activity at subduction zones. Tectonically exhumed peridotite at the Earth's surface provides a substantial sink for water and carbon. The natural chemical disequilibrium that exists between exposed mantle peridotite and the surface waters/atmosphere could potentially be harnessed as a negative carbon emission technology. Understanding this process is therefore critical from both a petrological and environmental perspective. Retrograde metamorphism is physically complex, potentially involving an interplay between positive (cracking) and negative (clogging) feedbacks that may limit, or promote, fluid supply to unreacted minerals. Modeling studies are important in helping to constrain the conditions that control the extent of reaction in ultramafic rocks. This study builds on a previously reported model that describes olivine hydration/carbonation in a poroelastic medium, coupling fluid flow, elastic deformation, and mass transfer between chemically active phases. Here we extend this model to include brittle failure, which is crucial given the widely held hypothesis that reaction-driven cracking is the dominant positive feedback in these processes. Here we explore the use of phase-field methods to simulate brittle failure in a poroelastic medium, in the context of hydration (serpentinization) of peridotite. We show that reaction-driven cracking in this model can generate a positive feedback that, under certain conditions, can lead to 100% transformation of olivine to serpentine.