Variable Behaviors of 3D Subducted Slabs and Their Influence On The Thermal and Chemical Heterogeneities In Earths lowermost Mantle

地球的最外层由几个连续的板块（“构造板块”）组成，这些板块不断地相互碰撞、拉开或滑过。密度更大的板块可能会潜入其他板块（或“潜没”）之下，而不是迎头相撞，我们可以在地震波拍摄的地球深部图像中看到这些潜没的“板块”（类似于医院的CT扫描）。这些地震图像显示，俯冲板块有各种形状，在地幔底部附近，它们与异常物质堆有关，这些异常物质可能比板块或周围的地幔更热，成分也不同。 Li和他的团队将使用超级计算机进行许多最先进的计算，以模拟俯冲板的行为及其与周围环境的相互作用。该项目将导致全面了解为什么板块具有不同的形状以及它们如何影响深部地幔的化学，结构和温度。地震研究揭示了地幔深部俯冲板片的多种形态。板块向地幔最低层的俯冲以及由此产生的热/化学不均匀性通常被认为是造成广泛地震异常的原因（例如，超低速区，散射体）以外的两个大的低速省（LLVPs）。然而，目前还不清楚是什么控制板片形态和俯冲板片与不同的形态控制的形成和分布的热/化学不均匀性在相对较冷的地区的最低地幔以外的LLVPs。该项目旨在使用具有类似地球的单侧俯冲的三维（3D）模型来解决这些问题。该团队将首先彻底探索3D纯热模型中的参数空间，以建立一个模型库，显示最低地幔中板片动力学和形态的不同场景。之后，该团队将为不同的板情景选择代表性模型，并引入多个组成组件（例如，将大洋地壳、亏损岩石圈、低应变速率物质（LLVP物质）引入模型域，进行三维高分辨率（高达几公里）热化学模型，研究不同动力学和形态的俯冲板片如何影响热异常的形成，以及俯冲洋壳在低应变速率物质以外地幔下部相对寒冷区域的分凝、聚集和分布。该项目将从根本上推进我们对精细尺度3D板片形态和动力学的长期时间变化的理解，以及它们对地球最低地幔中的热和化学不均匀性以及地震不均匀性的贡献，该奖项反映了NSF的法定使命，并通过利用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

The Earth’s outermost shell comprises several coherent pieces ("tectonic plates") that continually collide, pull apart, or slide past each other. Denser plates may dive below other plates (or "subduct") rather than colliding head on, and we can see these subducted "slabs" in images of the deep Earth made with seismic waves (analogous to a hospital CT scan). These seismic images show that subducted slabs have a variety of shapes, and near the bottom of the mantle they are associated with piles of anomalous material that is likely hotter and compositionally different from either the slabs or the surrounding mantle. Li and his team will perform many state-of-the art computations using supercomputers to simulate the behavior of subducted slabs and their interactions with their surroundings. This project will lead to a comprehensive understanding of why slabs have different shapes and how they influence the chemistry, structure, and temperatures of the deep mantle. Seismic studies have revealed a variety of morphologies of subducted slabs in the deep mantle. The subduction of slabs to the lowermost mantle and the resulted thermal/chemical heterogeneities at this depth are often thought to be responsible for the wide-spread seismic anomalies (e.g., ultra-low velocity zones, scatterers) outside the two large low velocity provinces (LLVPs). However, it remains unclear what controls slab morphology and how subducted slabs with different morphology control the formation and distribution of thermal/chemical heterogeneities in the relatively cold regions of the lowermost mantle outside the LLVPs. This project aims to address these questions using 3-dimensional (3D) models with Earth-like single-sided subduction. The team will first exhaustively explore the parameter space in 3D purely thermal models to build a library of models that show different scenarios of slab dynamics and morphology in the lowermost mantle. After that, the team will select representative models for different slab scenarios and introduce multiple compositional components (e.g., oceanic crust, depleted lithosphere, LLVP materials) to the model domain, and perform 3D high-resolution (up to a few km) thermochemical models, to study how subducted slabs with different dynamics and morphology affect the formation of hot thermal anomalies, and the segregation, accumulation, and distribution of subducted oceanic crust in the relatively cold regions of the lowermost mantle outside the LLVPs. This project will fundamentally advance our understanding of the long-term temporal variation of fine-scale 3D slab morphology and dynamics, and their contributions to the thermal and chemical heterogeneities and thus seismic heterogeneities in Earth’s lowermost mantle, especially outside the LLVPs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.