Effects of Serpentinization on Hydrothermal Systems: Modelling the Ultramafic-Hosted Rainbow Hydrothermal Field

Serpentinization is a common geochemical process in ultramafic-hosted hydrothermal systems, where the hydration of mantle rocks releases heat and hydrogen that can support hydrothermal circulation and chemosynthetic ecosystems. Most current understanding of serpentinization kinetics and thermodynamic limits is primarily derived from closed-system laboratory experiments. Here, we investigate how this reaction operates within dynamically circulating fluid systems in nature. A simplified model for serpentinization as a function of temperature and fluid velocity was developed and implemented via three-dimensional numerical simulations using the IC-FERST flow simulator.  Flow simulations explore how serpentinization interacts with fluid circulation and responds to variations in rock porosity and permeability. We apply this framework to a geologically realistic model of the Rainbow hydrothermal field (north Mid-Atlantic Ridge) to evaluate the combined effects of a deep magmatic heat source and reaction-driven heat generation. Results indicate that while the high vent temperatures and heat fluxes observed at Rainbow require a magmatic driver, serpentinization works synergistically with magmatic heat to temporarily elevate vent temperatures (by up to 50°C) and substantially increase seabed heat and fluid fluxes. Rather than being a uniformly progressing front, the serpentinization reaction is most effective in permeable regions surrounding the upwelling plume, where temperatures remain within an optimal thermodynamic window. Heat released by serpentinization has the unexpected effect of making upwelling plumes more stable in space and time, potentially contributing to sustaining black smoker vent fields over long periods of time (>10k years). By capturing key characteristics of the observed discharge at Rainbow, this study highlights how chemical reactions and fluid circulation jointly regulate hydrothermal activity and hydrogen production in ultramafic systems.