Geophysical Continuum Modeling from Pore to Planetary Scales

在这项提议中，我列出了一项计划，利用连续介质物理的数值模拟来促进我们对地球内部状态和地球内部流体运输的了解。所涉及的长度尺度从行星尺度(1000公里)到岩石孔隙尺度(微米)不等。一种行星尺度的现象涉及在多孔层中将孔隙率分离成带状结构，当系统受到外部施加的剪切时，固体可以像非常粘性的液体一样变形。这些结构可能存在于地球的上地幔中，并可能为在大洋中脊有效地提取地幔熔体形成新的洋壳提供了一种手段。在实验室对部分熔融岩石的剪切实验中发现的这些带，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起到重要作用。在这项提议中，我描述了更好地理解这些带的动力学并确定它们对地幔熔体输送和地幔动力学的重要性的建模工作。熔化和凝固的热和成分效应也将包括在这些研究中。同样在行星尺度上，了解地幔中正在发生的热对流过程也是非常重要的。地幔对流是驱动板块构造的引擎，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。我提议用表面板进行对流的流体力学模拟，以更好地了解地球的热状态及其随时间的热量收支。将被模拟的一种影响将是板下面的低粘性层，这可能是由多孔带引起的。我还计划通过耦合地幔对流模型和孔隙带形成模型来模拟从地球内部提取熔体的过程。在孔隙尺度上，了解流体和电流等过程是如何发生的是至关重要的，这样我们才能理解更大长度尺度上的过程，如地幔中熔体的运输。我计划模拟连续体现象，比如流体通过岩石的孔隙空间流动，这些现象是用先进的成像技术，如X射线断层成像技术拍摄的。利用岩石的数字表示，我和我的学生将模拟流体和电流通过孔隙路径的流动，以表征渗透率和电性地层系数。此外，我们还打算考虑多相流和流体与孔壁之间的化学反应的影响。例如，这些影响是石油回收和矿化的重要因素，可能具有重要的经济意义。此外，我们还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。在中等(厘米长)的尺度上，我建议进行与飞溅状钙钛矿形成相关的模拟。这些岩石代表着冻结的液滴，这些液滴是在一次大的地球撞击后熔融的硅酸盐岩石飞溅的结果。我和我的学生将把描述岩石冷却的热模型与包括旋转和表面张力影响的变形模型结合起来，以便更好地理解这些物体的最终形状。我还建议分析它们表面的高分辨率图像，以研究气泡坑和纹影等表面特征，以洞察这些神秘岩石的变形历史。通过在一系列长度尺度上研究这些现象，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.