4D quantification of micro-scale feedbacks in dehydrating, deforming rocks

本研究项目采用一种新颖的方法来确定在何处矿物脱水反应可以引发变形岩石的破坏。脱水和破坏之间的这种联系在收敛的板块边界处是重要的。在板块碰撞的地方，地壳的浅层部分受到所谓的薄皮构造的影响。在那里，脱水反应使构造推覆体的就位成为可能，这些推覆体形成了瑞士侏罗山脉或美国阿巴拉契亚山脉等山带。板块碰撞还会导致构造板块的俯冲，在那里，脱水反应被怀疑会引发几十公里深处的地震事件。在这两种构造环境中，随着温度的升高，岩石中的含水矿物变得不稳定。它们在脱水反应中释放水分，开始转化为密度更大的矿物质。密度的增加产生了孔隙，这些孔隙被水填满。孔隙、孔隙中的流体压力和新生长的矿物质在机械上削弱了正在反应的岩石。它可能变得无法支撑构造应力而失效。控制大规模构造的过程始于颗粒尺度。这些颗粒尺度过程涉及一系列复杂的、相互交织的发展，涉及岩石脱水的化学、水力学和力学。耦合的化学、水力和机械过程可能促进脱水岩石的自组织，使其最终失效。不幸的是，无论是经典的实验室实验还是基于现场的研究都不能在微观尺度上对这些耦合过程进行时空（4D）表征。因此，解释岩石脱水破坏的模型缺乏可靠的观测基础。我们将使用一种独特的新方法组合来克服这一严重的限制。我们由经验丰富的跨学科研究人员组成的团队将建立一种直接观察变形岩石脱水反应的技术。我们将采用英国和瑞士最强大的x射线源，在新一代实验压力容器中观察脱水反应。这些容器对x射线是透明的，使我们能够重现构造推覆体底部和俯冲带中深度的情况。它们是在爱丁堡设计和建造的。将这些血管与时间分辨（4D） x射线显微断层扫描相结合，将使我们能够在广泛的条件下记录矿物脱水。由此产生的4D微层析成像数据集将具有数十TB的体积。基于机器学习的新分析技术将使我们能够从这些大量数据中提取相关信息。我们的分析将确定脱水导致岩石无法承受构造应力的条件。利用这些分析，我们将测试和推进用于在数值模拟中联系脱水和变形的理论概念。首次直接观察脱水反应过程中复杂的颗粒尺度发展将大大促进我们对构造过程中一些关键过程的理解。由于我们的数据是时间分辨的和动态的，因此它们将支持对现场数据的解释，否则将捕获静态的脱水反应化石图像。我们的数据将允许测试和改进现有的数学模型，为大规模构造过程的强大模拟提供基础。最终，我们的发现将支持与板块碰撞相关的风险评估。我们的项目还将为地热能、二氧化碳封存和核废料储存的研究提供一种新的实验成像方法。该方法结合了我们的新实验血管的时间分辨x射线微断层扫描，先进的数据挖掘，图像分析和计算模拟。

This research project uses a novel methodological approach to determine where mineral dehydration reactions can trigger failure in deforming rocks. This link between dehydration and failure is important at convergent plate boundaries. Where plates collide, the shallow portions of the Earth's crust are affected by so-called thin-skinned tectonics. There, dehydration reactions enable the emplacement of tectonic nappes, which shape mountain belts such as the Swiss Jura, or the Appalachians in the US. Plate collision also leads to the subduction of tectonic plates, where dehydration reactions are suspected to trigger seismic events at depths of several tens of kilometers. In both tectonic settings hydrous minerals in rocks become unstable as temperature increases. They start to transform into denser minerals by releasing water in dehydration reactions. The density increase produces pores, which are filled by the water. The pores, the fluid pressure in them, and the newly grown minerals weaken the reacting rock mechanically. It may become unable to support tectonic stresses and fail. The processes that control large-scale tectonics start at the grain scale. These grain scale processes entail a series of complicated, intertwined developments that involve the chemistry, hydraulics and mechanics of a dehydrating rock. Coupled chemical, hydraulic and mechanical processes may facilitate the self-organization of the dehydrating rock into a state where it ultimately fails. Unfortunately, neither classical laboratory experiments nor field-based studies allow a spatial and temporal (4D) characterization of these coupled processes on the micro-scale. Models to explain failure in dehydrating rocks therefore lack a robust observational basis.We will use a unique combination of new methods to overcome this severe limitation. Our interdisciplinary team of experienced researchers will establish a technique to directly observe dehydration reactions in deforming rocks. We will employ the most powerful x-ray sources in the UK and Switzerland to observe dehydration reactions in a new generation of experimental pressure vessels. These vessels are transparent to x-rays and allow us to reproduce conditions at the base of tectonic nappes and at intermediate depths in subduction zones. They are designed and built in Edinburgh. Combining these vessels with time-resolved (4D) x-ray microtomography will enable us to document mineral dehydration at a wide range of conditions. The resulting 4D microtomography data sets will have a volume of several tens of TB. New analysis techniques based on machine learning will allow us to extract the relevant information from these vast quantities of data. Our analyses will determine conditions where dehydration causes rocks to become unable to support tectonic stresses. Using these analyses, we will test and advance theoretical concepts used to link dehydration and deformation in numerical simulations.The first direct observation of the complex grain-scale developments during dehydration reactions will significantly advance our understanding of some key processes in tectonics. Because our data are time-resolved and dynamic, they will support the interpretation of field data that otherwise capture a static, fossilized picture of dehydration reactions. Our data will allow testing and refining existing mathematical models that provide a foundation for robust simulations of large-scale tectonic processes. Ultimately, our findings will support the assessment of risks associated with plate collision. Our project will also make a new experimental imaging method available for research on geothermal energy, CO2 sequestration and nuclear waste storage. The method combines time-resolved x-ray microtomography in our new experimental vessels with advanced data mining and image analysis and computational simulation.