Deformation Mechanics of an Asperity under Hydrothermal Conditions

压力解是一种涉及大陆地壳较浅深度的含流体颗粒岩的变形机制。这种溶液输送机制在自然过程中很重要，包括沉积物压实、沉积盆地沉降、断层强化和地壳造山运动，以及工程和工业应用，如含水层的表征、污染物的输送、石油勘探和生产、地热能回收、核废料处理和二氧化碳封存。尽管有大量证据表明这一无处不在的过程的重要性，但尚不存在详细的本构定律，使科学家能够预测自然条件下的变形速率。在这个项目中，正在进行数值实验和实验室测试，以研究颗粒材料中小凸起处变形的物理和动力学。这些实验是由麻省理工学院的学生和工作人员与门洛帕克美国地质调查局的S.希克曼和N.比勒合作完成的。该实验旨在测量石英或蓝宝石板在高达600℃的温度和150 MPa或更小的流体压力下1-4周的变形。在最初的实验室实验中，蓝宝石被用作“不溶性”矿物的替代品，因为它易于抛光、坚固、透明，足以用作窗户材料。使用光学、透射电子和扫描电子显微镜观察变形后接触区产生的微观结构。除了实验室实验外，还进行了数值计算来研究输运、溶解和沉淀过程的耦合，应力分布变化的影响，瞬态的产生或衰减，以及粗糙变形动力学与组成过程动力学的关系。最初的数值模型表明，这些过程的耦合比以前认为的要复杂得多。此外，这些计算预测了一个相当长的瞬变周期，如果得到证实，这对于理解实验室实验是否能准确地推断出自然条件至关重要。

Pressure solution is a deformation mechanism involving fluid-laden granular rocks at relatively shallow depths in the continental crust. Such solution transport mechanisms are important during natural processes, including the compaction of sediments, subsidence of sedimentary basins, fault strengthening, and crustal orogeny, and for engineering and industrial applications, such as the characterization of aquifers, transport of pollutants, oil exploration and production, geothermal energy recovery, nuclear waste disposal, and carbon dioxide sequestration. Although there is copious evidence of the importance of this ubiquitous process, a detailed constitutive law does not exist that would enable scientists to predict the rate of deformation under the natural conditions. In this project, both numerical experiments and laboratory tests are being conducted to investigate the physics and kinetics of deformation at small asperities in granular materials. The experiments are being done by students and staff at the Massachusetts Institute of Technology, in collaboration with S. Hickman and N. Beeler, USGS, Menlo Park. The experiments are designed to measure deformation of quartz asperities pressed against either quartz or sapphire plates at temperatures up to 600 C and fluid pressures of 150 MPa or less for periods of 1-4 weeks. For the initial lab experiments, sapphire is being used as a proxy "insoluble" mineral because it is easily polished, strong, and transparent enough to be used as a window material. The microstructure produced at the contact region is being observed after deformation using optical, transmission electron, and scanning electron microscopy. In addition to the laboratory experiments, numerical calculations are being performed to investigate the coupling of transport, dissolution, and precipitation processes, the effect of variations in stress distribution, the production or decay of transients, and the relation of the kinetics of the asperity deformation to the kinetics of the component processes. Initial numerical models suggest a much more intricate coupling of the processes than thought heretofore. In addition, the calculations predict a rather long transient period that will, if confirmed, be critical to understand if laboratory experiments are to be extrapolated accurately to natural conditions.