CSEDI: Integrated seismic, geodynamic, and mineral physics studies of the deepest lower mantle

行星深处物质的行为有助于推动产生板块构造的流动。由深地幔源驱动的大量火成岩喷发被认为是导致全球环境变化的原因。位于地球表面以下约3000公里处的核幔边界区是地球上最引人注目的成分和热边界层之一。穿过这一边界的对流对行星的冷却、地核的动力学（以及地球的磁场）和地幔的动力学（可能表现为地球表面的大规模火山活动）产生主要影响。通过实验和计算设施和技术、仪器分辨率和USAray的部署，在理解地球深部系统动力学方面取得了重大进展。利用这些重大进展以及该团队在地震学，地球动力学和实验矿物物理学方面的个人专业知识，该团队将在地幔流框架内研究俯冲板片与多尺度下地幔结构的相互作用。他们将指导在多学科环境中工作的下一代科学家，这将提高对地球作为一个全球系统如何运作的理解。 地震学家已经揭示，CMB的地幔一侧是非常不均匀的，具有公里级的精细结构，可能含有不同的化学储层。热和化学的不均匀性，固-固相变，弹性各向异性，可变粘度和熔化可能都需要解释这种观察到的复杂性。凭借地震学（Helmberger和Zhan）、地球动力学（Gurnis）和实验矿物物理学（杰克逊）方面的专业知识，他们将把原子尺度（地球深部相的热弹性特性）与构造尺度（地震观测到的结构及其动力学）联系起来，并将所有过程与时间维度联系起来（构造板块历史的重建）。他们将使用完整的地震图与现有增强层析成像模型和可压缩热化学对流与合理的板块构造重建生成的合成图进行比较，对太平洋大型低地震速度区（LLSVP）进行系统研究。将对太平洋和非洲的LLSVPs进行详细比较，以测试构造历史的影响、地震各向异性的存在以及可能的成分和/或热差异。这些实验通过对（Mg0.22Fe0.78）O镁钨华单晶的非弹性X射线散射和衍射实验评估了（1）地震各向异性的来源;通过对洋中脊玄武岩相组合的X射线衍射实验评估了地震梯度和不连续性的来源。他们的研究最终将产生一个最新的全球CMB区域地图。他们将解决的基本问题包括：俯冲板的存在是否可以将LLSVP变形为地震可分辨的3D形状？富铁（Mg，Fe）O是由俯冲板片附近的地幔流动形成的可观测地震各向异性的来源吗？这些板块如何相互作用并影响D？LLSVP边缘附近的地形和化学上不同的结构？

The behavior of deep planetary materials helps drive the flows that produce plate tectonics. Voluminous igneous eruptions driven by deep mantle sources are thought to have caused global environmental changes. Located approximately 3000 km below the surface of the planet, the core-mantle boundary region represents one of the most dramatic compositional and thermal boundary layers within our planet. Gradients across this boundary exert a primary influence on the cooling of the planet, on the dynamics of the core (and hence Earth's magnetic field), and on the dynamics of the mantle (perhaps expressed as large-scale volcanism at the Earth's surface). Major progress towards understanding the dynamics of the deep Earth system within various geoscience disciplines has been made possible through advances in experimental and computational facilities and techniques, instrumental resolution, and deployment of the USArray. Capitalizing on these major advancements and the team's individual expertise within seismology, geodynamics, and experimental mineral physics, the team will study the interaction of subducted slabs with multi-scale lower mantle structures in the framework of mantle flow. They will mentor next generation scientists working in their multi-disciplinary environment, which should improve understanding of how the planet works as a global system. Seismologists have revealed that the mantle side of the CMB is extraordinarily heterogeneous, with km-scale fine structure that could harbor distinct chemical reservoirs. Thermal and chemical heterogeneity, solid-solid phase transitions, elastic anisotropy, variable viscosity, and melting are probably all required to explain this observed complexity. With individual expertise in seismology (Helmberger and Zhan), geodynamics (Gurnis), and experimental mineral physics (Jackson), they will connect the atomic scale (thermoelastic properties of deep Earth phases) to the tectonic scale (seismically observed structures and their dynamics) and link all processes to the temporal dimension (reconstruction of tectonic plate history). They will conduct a systematic study of the Pacific large low seismic velocity province (LLSVP) using whole seismograms compared against synthetics generated from existing enhanced tomographic models and compressible thermo-chemical convection with reasonable plate tectonic reconstructions. A detailed comparison of the Pacific and African LLSVPs will be done to test the impact of tectonic histories, presence of seismic anisotropy, and possible compositional and/or thermal differences. The experiments assess the sources of (1) seismic anisotropy through inelastic x-ray scattering and diffraction experiments on single crystals of (Mg0.22Fe0.78)O magnesiowüstite (2) seismic gradients and discontinuities through x-ray diffraction experiments on mid-oceanic ridge basalt phase assemblages. Their study will culminate with generating an updated global map of the CMB region. The fundamental questions they will address include: Can the presence of subducted slabs deform LLSVPs into seismically resolvable 3D shapes? Is iron-rich (Mg,Fe)O a source of observable seismic anisotropy, developed by flow of the mantle near subducting slabs? How do these slabs interact and affect D? topography and chemically-distinct structures near the edges of LLSVPs?