Geophysical Continuum Modeling from Pore to Planetary Scales

在这个提案中，我提出了一个计划，利用连续介质物理的数值模拟来推进我们对地球内部状态和地球内部流体输运的认识。所涉及的长度尺度从行星尺度（几千公里）到岩石孔隙尺度（微米）不等。一个行星尺度的现象涉及到多孔层中孔隙度的分离成带结构，当系统受到外部施加的剪切时，固体会像非常粘稠的液体一样变形。这些构造可能存在于地球的上地幔中，并可能为地幔熔体在洋中脊处被有效地提取出来形成新的海洋地壳提供了一种手段。这些在实验室实验中看到的剪切部分熔融岩石的条带也可能降低地球上地幔的有效粘度，因此甚至可能对解释地球上板块构造的存在很重要。在本提案中，我描述了建模工作，以更好地理解这些带的动力学，并确定它们对地幔熔体运输和地幔动力学的重要性。熔化和凝固的热效应和成分效应也将包括在这些研究中。同样在行星尺度上，理解地幔中发生的热对流过程也是非常重要的。地幔对流是推动板块构造的引擎，也是地壳形成的原因。虽然地球的地幔是固体，但在很长的时间尺度上，它像液体一样流动。我提议对地表板块的对流进行流体力学模拟，以更好地了解地球的热状态及其随时间的热收支。一个将被模拟的效应将是由孔隙带引起的板下低粘度层。我还计划通过将地幔对流模型与孔隙带形成模型相结合来模拟从地球内部提取熔融物的过程。在孔隙尺度上，理解流体和电流流动等过程是如何发生的至关重要，这样我们才能理解更大尺度上的过程，比如地幔中熔体的运输。我计划模拟连续现象，比如流体流过岩石孔隙空间，用x射线断层扫描等先进成像技术进行成像。使用岩石的数字表示，我和我的学生将模拟流体和电流通过孔隙通道，以表征渗透率和电地层因子。此外，我们打算纳入多相流和流体与孔壁之间的化学反应的影响。这些影响是重要的因素，例如，石油开采和矿化可能具有重要的经济意义。此外，我们打算模拟孔隙流体和岩石基质组合的变形，以研究岩石和孔隙流体组合的有效弹性和粘度。在一个中等（厘米长度）的尺度上，我建议进行与飞溅状陨石形成有关的模拟。这些岩石代表了地球大碰撞后熔融硅酸盐岩石飞溅产生的冷冻液滴。为了更好地理解这些物体的最终形状，我和我的学生将结合一个热模型来描述岩石的冷却过程，并结合一个变形模型，其中包括旋转和表面张力的影响。我还建议分析其表面的高分辨率图像，研究气泡坑和纹影等表面特征，以深入了解这些神秘岩石的变形历史。通过在一定长度范围内考察这些现象，我们将更好地了解地球及其演化。

In this proposal, I lay out a plan to advance our knowledge of Earth’s internal state and the transport of fluids inside the Earth using numerical modeling of continuum physics. The length scales involved range from planetary scales (1000s of kms) to the scales of rock pores (microns). One planetary scale phenomenon involves the segregation of porosity into band structures in porous layers where the solid can deform like a very viscous liquid when the system is subjected to an externally imposed shear. These structures may exist in Earth’s upper mantle and may provide a means for mantle melts to be extracted efficiently at mid-ocean ridges to form new oceanic crust. These bands, which are seen in laboratory experiments of sheared partially molten rocks, may also reduce the effective viscosity of Earth’s upper mantle and may therefore even be important for explaining the existence of plate tectonics on Earth. In this proposal, I describe modeling efforts to better understand the dynamics of these bands and to determine their importance for mantle melt transport and mantle dynamics. The thermal and compositional effects of melting and solidification will also be included in these studies. Also at the planetary scale, it is very important to understand the process of thermal convection that is taking place in Earth’s mantle. Mantle convection is the engine that drives plate tectonics and is responsible for the formation of Earth’s crust. Although Earth’s mantle is a solid, on long time scales it flows like a liquid. I am proposing to carry out fluid-mechanical simulations of convection with surface plates to better understand Earth’s thermal state and its heat budget over time. One effect that will be modeled will be a low viscosity layer beneath the plates which may be caused by porosity bands. I also plan to model the extraction of melt from Earth’s interior by coupling a mantle convection model with a model of porosity band formation. At the pore scale, it is crucial to understand how processes like fluid and electrical flow occur in order that we can understand processes on much larger length scales like the transport of melt in Earth’s mantle. I plan to simulate continuum phenomena like fluid flows through the pore spaces of rocks imaged with advanced imaging techniques like X-ray tomography. Using digital representations of rocks, my students and I will simulate fluid and electrical flows through the pore pathways in order to characterize the permeability and electrical formation factor. Also, we intend to incorporate effects of multiphase flows and of chemical reactions between the fluid and pore walls. These effects are important factors in, for instance, oil recovery and mineralization that may be of economic importance. Additionally, we intend to simulate the deformation of the combined pore fluid and rock matrix in order to investigate the effective elasticity and viscosity of the rock and pore fluid combination. At an intermediate (cm length) scale, I am proposing to carry out simulations related to the formation of splash-form tektites. These rocks represent frozen fluid drops that result from the splash of molten silicate rock following a large Earth impact. My students and I will couple a thermal model to describe the cooling of the rock with a model of deformation that includes the effects of rotation and surface tension in order to better understand the final shapes of these objects. I also propose to analyze high resolution images of their surfaces to study surface features like bubble pits and schlieren to gain insight into the deformation histories of these enigmatic rocks. By examining these phenomena at a range of length scales, we will better understand Earth and its evolution.