CSEDI: Coupled Electromagnetic and Geodynamic Study of Thermochemical Piles

在过去的几十年里，地球科学的伟大成就之一是人们对地球内部的地质、热力和化学复杂性的认识日益加深。地球内部的范围从几公里深处一直延伸到液态外核的外部边界。这种复杂性是几个相互关联的地球物理观测的结果，这些观测不仅揭示了地球行星演化状态的当前快照，而且还揭示了46亿年全球尺度地球动力学过程和事件的历史记录，这些过程和事件塑造了我们赖以生存的地表以及海洋和大气。我们的研究重点是通过研究被称为热化学堆的神秘结构来进一步了解地球的“深层历史”，这些结构位于地幔底部附近，就在地核边界之上。这些构造的横向范围、大小、温度、组成和地质意义目前是一个非常有趣的主题，因为它们与火山的起源、现代构造板块的驱动力和很久以前俯冲构造板块的命运有潜在的关系。然而，它们离地球表面很遥远——大约在地下3000公里——这使得它们成为地球物理研究的一个特别难以捉摸的目标。由于固有的分辨率限制和对全谱地质物质特性的选择性敏感性，没有一种地球物理方法足以描绘地球这一地区的完整图景。我们建议通过一套全面的数值实验和与观测数据的比较，研究下地幔的热化学状态，并采用相互兼容的电磁和地球动力学模型。这些方法的结合是基于电磁观测对地幔电导率表现出的热化学变异性的强敏感性，以及地球动力学建模对物质参数（如密度和粘度）的敏感性，这些参数控制着下地幔中物质的积累及其热结构。这些实验的核心是一个首要问题：我们如何或能够通过地球动力学兼容的电磁观测来限制我们对最下层地幔热物理化学状态的了解？计算实验将使用一个新的并行电磁地幔感应模拟器（项目MANTIS）进行，用于分布式内存计算架构，它与将用于地球动力学模拟的CitcomS代码共享相同的底层数学离散化。两种编码之间离散化方法的兼容性对于最小化数值伪影非常重要，因为电磁域的材料属性被映射到地球动力域的相应属性。

One of the great accomplishments in the Earth Sciences in the last few decades has been an increasing appreciation for geologic, thermal, and chemical complexity of Earth's interior, spanning a distance from a few kilometers depth down to the outer boundary of the liquid outer core. This complexity is the result of several interconnected geophysical observations that reveal not only a current snapshot of Earth's state of planetary evolution, but also a 4.6 billion year historical record of global scale geodynamic processes and events that have shaped the surface upon which we live as well as the oceans and atmosphere. Our research focuses on furthering our understanding of Earth's 'deep history' by investigating enigmatic structures known as thermochemical piles, which reside near the base of the mantle, just above the boundary with the core. The lateral extent, size, temperature, composition and geologic significance of these structures is presently a subject of great interest because of their potential relationship to the origin of volcanoes, driving forces for present-day tectonic plates and the fate of long-ago subducted tectonic plates. However, their remoteness from Earth's surface - roughly 3000 kilometers down - makes them an especially elusive target for geophysical investigation. Because of inherent resolution limits and selective sensitivity to the full spectrum of geomaterial properties, no single geophysical method is sufficient for painting a complete picture of this region of the Earth. We propose to study the thermochemical state of the lower mantle through a comprehensive set of numerical experiments, and comparison to observational data, for mutually compatible electromagnetic and geodyamic models. The union of these methods is based on the strong sensitivity of electromagnetic observations to thermochemical variability as manifested in the mantle's electrical conductivity, and the sensitivity of geodynamics modeling to material parameters such as density and viscosity that control the accumulation of material in the lower mantle and that material's thermal structure. Central to these experiments is the over-arching question: How do we, or can we, constrain our knowledge of the thermo-physio-chemical state of the lowermost mantle through geodynamically-compatible electromagnetic observations? Computational experiments will be conducted with a new, parallel electromagnetic MANTle Induction Simulator (project MANTIS) for distributed memory compute architectures, which shares the same underlying mathematical discretization as the CitcomS code that will be used for the geodynamic simulations. This compatibility between discretization methods between the two codes is important for minimizing numerical artifacts as material properties from the electromagnetic domain are mapped into corresponding properties in the geodynamic domain.