Geophysical Continuum Modeling from Pore to Planetary Scales

从孔隙到行星尺度的地球物理连续体建模

• 批准号: RGPIN-2014-04543
• 负责人: Butler, Samuel
• 金额: $ 2.19万
• 依托单位: University of Saskatchewan
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611100
• 关键词: Geophysical; Continuum; Modeling; Pore; Planetary

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.

在这个建议中，我提出了一个计划，以提高我们的地球内部状态和使用连续介质物理学的数值模拟地球内部的流体传输的知识。所涉及的长度尺度范围从行星尺度（1000公里）到岩石孔隙尺度（微米）。 一种行星尺度的现象涉及多孔层中的孔隙度分离成带结构，其中当系统受到外部施加的剪切时，固体可以像非常粘稠的液体一样变形。这些结构可能存在于地球的上地幔，并可能提供一种手段，地幔熔体提取有效地在洋中脊形成新的洋壳。这些条带在实验室实验中被剪切的部分熔融岩石中看到，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。在这个建议中，我描述的建模工作，以更好地了解这些乐队的动态，并确定其重要性地幔熔体输送和地幔动力学。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，了解地幔中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运动的引擎，也是地壳形成的原因。虽然地幔是固体，但在长时间尺度上，它像液体一样流动。我建议进行流体力学模拟对流与表面板，以更好地了解地球的热状态和它的热预算随着时间的推移。将被模拟的一个效应是板下的低粘度层，其可能由孔隙带引起。我还计划通过将地幔对流模型与孔隙带形成模型相结合，对地球内部熔体的提取进行建模。 在孔隙尺度上，了解流体和电流等过程如何发生是至关重要的，以便我们能够了解更大长度尺度上的过程，如地幔中熔体的运输。我计划模拟连续现象，比如用先进的成像技术（如X射线断层扫描）成像的岩石孔隙中的流体流动。使用岩石的数字表示，我的学生和我将模拟通过孔隙通道的流体和电流，以表征渗透率和电气地层因素。此外，我们打算将多相流和流体和孔壁之间的化学反应的影响。这些影响是重要的因素，例如，石油回收和矿化，可能具有经济重要性。此外，我们打算模拟组合的孔隙流体和岩石基质的变形，以研究岩石和孔隙流体组合的有效弹性和粘性。 在中等（厘米长度）规模下，我建议进行与飞溅状玻璃陨石形成相关的模拟。这些岩石代表了由熔融硅酸盐岩石在大规模地球撞击后飞溅而成的冻结液滴。我和我的学生将结合一个热模型来描述岩石的冷却，并结合一个变形模型，其中包括旋转和表面张力的影响，以便更好地理解这些物体的最终形状。我还建议分析其表面的高分辨率图像，以研究气泡坑和纹影等表面特征，从而深入了解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变。