A reactive transport approach for determining cause-and-effect redox relationships in elevated-temperature Earth systems

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Coupled reduction and oxidation (redox) reactions form the chemical underpinnings of many of the processes that we, both as biological organisms and as a society, rely on to live. The objective of this 5-year research program is to develop a comprehensive experiment-, characterization-, and modeling-based reactive transport approach to Fe and C redox processes during serpentinization and silicate diagenesis. These two sets of redox reactions have occurred in the igneous and sedimentary rocks underlying the oceans throughout Earth history. They influence and record global biogeochemical and tectonic cycles, concentrate societally important resources, and fuel various rock-hosted ecosystems. Reactive transport models (RTMs) provide a sophisticated numerical tool for simulating the many coupled processes occurring in these systems, which, in turn, should allow them to predict how a particular system will respond to geologic forcings. In other words, RTMs should allow researchers to distill simplified "cause-and-effect" relationships out of complex Earth systems. However, RTMs currently struggle to model these redox reactions. The innovative approach developed in this research program will build upon recent advancements in analytical capabilities, experimental techniques, and supercomputer-enabled RTMs to explore these individual cause-and-effect relationships. Using this approach, we will explore: 1) the impact of evolving hydraulic properties (i.e., porosity/permeability) on hydrothermal fluxes of reduced gases (hydrogen, H2 and methane, CH4) from serpentinization; 2) the underappreciated role of fluid inclusions in the fluxes of H2 and CH4 from low-temperature serpentinization; 3) the consequences of changes in seawater geochemistry over Earth history on the fluxes of these reduced gases; and 4) the role of organic matter in mineralogical transformations during burial of Fe-bearing sediments. We will particularly work to apply hydrogeologic characterization methods, experiments doped with anomalous isotopes, and international x-ray and neutron beam facilities to characterize reaction processes in both the serpentinization and diagenesis systems. Importantly, this research program will: 1) provide a new, conceptual model describing the roles of individual processes on overall redox reactions during serpentinization; 2) permit enhanced predictions of Fe mineral behavior during hydrocarbon reservoir evolution, CO2 storage in sedimentary rocks, and global Fe and C cycling; and 3) Provide new experimental and characterization methods for quantifying a broad range of geological processes. Together, these results will enhance our collective understanding of Canada's natural environment and the ways in which it can be sustainably exploited for societal benefit.