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

耦合还原和氧化（氧化还原）反应构成了我们作为生物有机体和社会赖以生存的许多过程的化学基础。这项为期5年的研究计划的目标是在蛇纹石化和硅酸盐成岩作用过程中，开发一种基于实验、表征和建模的铁和C氧化还原过程的综合反应传输方法。这两组氧化还原反应在整个地球历史上都发生在海洋下面的火成岩和沉积岩中。它们影响并记录了全球生物地球化学和构造循环，集中了重要的社会资源，并为各种岩石承载的生态系统提供燃料。反应输运模型（RTMs）为模拟这些系统中发生的许多耦合过程提供了一个复杂的数值工具，这反过来又使他们能够预测特定系统对地质作用力的反应。换句话说，rtm应该允许研究人员从复杂的地球系统中提炼出简化的“因果”关系。然而，rtm目前很难模拟这些氧化还原反应。在这个研究项目中开发的创新方法将建立在分析能力、实验技术和超级计算机支持的rtm的最新进展之上，以探索这些个体的因果关系。利用这种方法，我们将探索：1)水力性质（即孔隙度/渗透率）的变化对蛇纹石化过程中还原性气体（氢，H2和甲烷，CH4）热液通量的影响；2)流体包裹体在低温蛇纹石化过程中H2和CH4通量中的作用未被充分认识；3)地球历史上海水地球化学变化对这些还原性气体通量的影响；4)有机质在含铁沉积物埋藏过程中的矿物学转化作用。我们将特别致力于应用水文地质表征方法，掺杂异常同位素的实验，以及国际x射线和中子束设备来表征蛇纹岩化和成岩系统中的反应过程。重要的是，该研究计划将：1)提供一个新的概念模型，描述蛇纹石化过程中单个过程在整体氧化还原反应中的作用；2)增强了对油气藏演化、沉积岩中CO2储存以及全球铁和碳循环过程中铁矿物行为的预测；3)为广泛的地质过程的量化提供新的实验和表征方法。总之，这些结果将增强我们对加拿大自然环境的集体理解，以及如何可持续地利用它来造福社会。

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.