Reactive fluid flow guided by grain-scale equilibrium reactions during eclogitization of dry crustal rocks

Abstract Fluid flow in crystalline rocks the absence of fractures or ductile shear zones dominantly occurs by grain boundary diffusion, as it is faster than volume diffusion. It is, however, unclear how reactive fluid guided through such pathways. We present a microstructural, mineral chemical, and thermodynamic analysis static fluid-driven reaction from dry granulite to ‘wet’ eclogite. infiltration resulted re-equilibration at eclogite-facies conditions, indicating that granulitic protolith was out equilibrium, but unable adjust changing P – T conditions. The transformation occurred three steps: (1) initial hydration along plagioclase boundaries, (2) complete breakdown phase boundaries between garnet/clinopyroxene, (3) rock an assemblage. Thermodynamic modelling local compositions reveals this sequence proportional decrease Gibbs free energy calculated for ‘dry’ cases. These differences result increased net rates reactions largest occur first. In addition, these leading porosity formation; i.e., pathways new enter site thus controlling flow. Element transport sites only if energetically beneficial, enough agent available. Reactive during nominally impermeable budget equilibrium domains.