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

耦合的还原和氧化(氧化还原)反应构成了我们作为生物有机体和作为一个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开发一种基于实验、表征和模拟的综合反应传输方法，以研究蛇纹岩和硅酸盐成岩过程中的Fe和C氧化还原过程。在整个地球历史上，这两组氧化还原反应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，并为各种以岩石为宿主的生态系统提供燃料。反应输运模型(RTM)为模拟这些系统中发生的许多耦合过程提供了一种复杂的数值工具，这反过来又使它们能够预测特定系统将如何响应地质压力。换句话说，RTMS应该能让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目前难以对这些氧化还原反应进行建模。在这个研究计划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使能的RTM方面的最新进步，以探索这些个体的因果关系。利用这种方法，我们将探索：1)不断演变的水力性质(即孔隙度/渗透率)对蛇纹岩还原气体(氢、氢和甲烷、CH4)热液通量的影响；2)流体包裹体在低温蛇纹岩作用产生的H2和CH4通量中的作用被低估；3)地球历史上海水地球化学变化对这些还原气体通量的影响；以及4)有机质在含铁沉积物埋藏过程中矿物转化中的作用。我们将特别致力于应用水文地质表征方法、异常同位素掺杂实验以及国际X射线和中子束设备来表征蛇纹岩和成岩系统中的反应过程。重要的是，这项研究计划将：1)提供一个新的概念性模型，描述蛇纹岩作用中单个过程对整体氧化还原反应的作用；2)增强对油气藏演化过程中的铁矿物行为、沉积岩中的二氧化碳储存以及全球Fe和C循环的预测；3)为量化广泛的地质过程提供新的实验和表征方法。总而言之，这些成果将加强我们对加拿大自然环境的集体了解，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.