Deformation Mechanics of an Asperity under Hydrothermal Conditions

压力溶解是一种变形机制，涉及大陆地壳中相对较浅深度的充满流体的粒状岩石。这种溶液输运机制在自然过程中是重要的，包括沉积物的压实、沉积盆地的沉降、断层强化和地壳运动，以及对于工程和工业应用，如含水层的表征、污染物的输运、石油勘探和生产、地热能回收、核废料处置和二氧化碳封存。虽然有大量的证据证明这个普遍存在的过程的重要性，但并不存在一个详细的本构律，使科学家能够预测自然条件下的变形速率。本计画将以数值实验与实验室实验相结合的方式，探讨粒状材料中微凸体变形的物理与动力学。这些实验是由马萨诸塞州理工学院的学生和工作人员与S。Hickman和N.比勒美国地质勘探局门洛帕克。实验设计为测量在高达600 ℃的温度和150 MPa或更低的流体压力下压靠石英或蓝宝石板的石英粗糙体的变形，持续1-4周。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，因为它很容易抛光，坚固，透明，足以用作窗户材料。在接触区域产生的显微组织正在观察变形后，使用光学，透射电子和扫描电子显微镜。除了实验室实验，数值计算正在进行调查的耦合的运输，溶解和沉淀过程中，应力分布的变化，瞬态的生产或衰减的影响，以及粗糙变形的动力学的组件过程的动力学的关系。最初的数值模型表明，这些过程的耦合比迄今为止所认为的要复杂得多。此外，计算预测了一个相当长的过渡期，如果得到证实，这对于理解实验室实验是否能准确地外推到自然条件至关重要。

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.