CSEDI: Structure and Dynamics of Large-Scale Lower Mantle Compositional Heterogeneity

本研究将重点研究太平洋下地幔非均质性的地震成像，并通过对流数值模拟将地震成像纳入一个动态一致的框架。我们的方法是多学科的，结合了PI Garnero的地震学分析和PI McNamara的地球动力学对流模拟。最近的地震学研究增加了太平洋下地幔深层结构的大量细节，有证据表明存在大型低剪切速度省（llsvp），它们比周围的地幔密度更大，在化学上也与周围的地幔不同。较小规模的结构包括可能优先位于LLSVP边缘的超低速度带（ulvz）。我们的高分辨率地震学实验旨在更好地解析似乎从核幔边界（CMB）向上延伸的尖锐的LLSVP边缘，以及强烈依赖于LLSVP和地幔性质的相关现象，包括：ULVZ的位置和结构、LLSVP边缘附近的CMB地形、LLSVP内部的强非均质性以及与LLSVP顶部羽流上涌的关系。我们关注的是在北美记录的西南太平洋俯冲带的地震数据，因为它们密集地采样了太平洋下的LLSVP，特别是在夏威夷下面。这是拟议工作的一个重点领域。地震结果将为包括LLSVP结构在内的地球动力学模拟提供信息。在动力学计算中，将特别注意LLSVP的形态和内部结构，因为这些特征将被地震成像。更好地对llsvp进行成像和建模将有助于我们进一步了解地球的热和质量传输机制，从而了解形成深部结构的对流驱动力。更好地理解地球深部地幔对流流动的本质，这种流动如何形成看似深而致密的成分储层，以及包括羽流在内的回流质量传递是这项工作的潜在动机。这项工作对于了解地球深处的结构和动力学非常重要。地球上对流的本质是什么？在地球和行星科学家的广泛研究范围内，这些流体是如何形成貌似深而致密的成分储层，以及包括羽流在内的回流质量传递，都是他们感兴趣的问题。该基金将资助一名从事跨学科研究项目的地球动力学研究生和一名从事地震成像和地球动力学计算的博士后研究员。pi在以跨学科的方式共同指导学生和博士后方面经验丰富。

This two-year proposal focuses on seismological imaging of lower mantle heterogeneity beneath the Pacific Ocean, and numerical convection simulations to put the seismic imaging into a dynamically consistent framework. Our approach is multidisciplinary, and combines seismological analyses by PI Garnero with geodynamical convection simulations by PI McNamara. Recent seismological work has added great detail to deep mantle structure beneath the Pacific, with evidence for large low shear velocity provinces (LLSVPs) that are denser than and chemically distinct from the surrounding mantle. Smaller scale structure includes ultra-low velocity zones (ULVZs) that may preferentially reside at LLSVP margins. Our high resolution seismological experiments aim to better resolve sharp LLSVP edges that appear to extend well up off the core-mantle boundary (CMB), and associated phenomena that depend strongly on LLSVP and mantle properties, including: ULVZ location and structure, CMB topography in vicinity of LLSVP edge, strong heterogeneity within the LLSVP, and relationship to plume upwelling off the LLSVP top. We are focusing on seismic data from southwest Pacific subduction zones recorded in North American, since they densely sample the LLSVP beneath the Pacific Ocean, especially beneath Hawaii. This is a focus area of the proposed work. The seismic findings will inform and be informed by geodynamic simulations that include LLSVP structures. Particular attention will be given to LLSVP morphology and internal structure in the dynamical calculations, as these features will be seismically imaged. Better imaging and modeling LLSVPs will help move us forward in understanding Earth's thermal and mass transport mechanisms, and hence the driving forces in convection that shape the deep structures. Better understanding the nature of convective flow in Earth's deep mantle, how that flow shapes plausible deep and dense compositional reservoirs, and return flow mass transfer that includes plumes is an underlying motivation in this work.This work is important for understanding the structure and dynamics of Earth's deep interior. The nature of convective flow in Earth?s deep mantle, how that flow shapes plausible deep and dense compositional reservoirs, and return flow mass transfer that includes plumes is of interest to the vast spectrum of Earth and planetary scientists. The funding is for a geodynamics graduate student who will be trained on an interdisciplinary research project, and a postdoctoral researcher focused on seismic imaging and geodynamics computations. The PIs are experienced at co-mentoring students and postdocs in a cross-disciplinary fashion.