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

CSEDI：最深下地幔的综合地震、地球动力学和矿物物理研究

• 批准号: 1600956
• 负责人: Jennifer Jackson
• 金额: $ 39.61万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1600956&HistoricalAwards=false
• 关键词: CSEDI; Integrated; seismic; geodynamic; mineral

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?

深部行星物质的行为有助于驱动产生板块构造的流动，由深部地幔源驱动的大量火成岩喷发被认为引起了全球环境变化，核心-地幔边界区域位于地球表面以下约 3000 公里处。地球上最引人注目的成分和热边界层之一，跨越该边界的梯度对地球的冷却、地核的动力学（以及地球的磁场）产生主要影响。地幔动力学（也许表现为地球表面的大规模火山活动）通过实验和计算设施和技术以及仪器分辨率的进步，在各个地球科学学科中理解地球深层系统的动力学方面取得了重大进展。以及 USArray 的部署，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。他们将指导下一代在多学科环境中工作的科学家，这将提高人们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，宇宙微波背景的地幔一侧是极其异质的，具有公里数。可能需要具有独特化学储库的尺度精细结构、固-固相变、弹性各向异性、可变粘度和熔化来解释这种观察到的复杂性。地震学（Helmberger 和 Zhan）、地球动力学（Gurnis）和实验矿物物理学（Jackson），他们将把原子尺度（深层地球相的热弹性特性）与构造尺度（地震观测到的结构及其动力学）联系起来，并将所有过程联系起来他们将使用完整的地震图与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。根据现有的增强层析成像模型和可压缩热化学对流以及合理的板块构造重建，将对太平洋和非洲 LLSVP 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。实验通过对单晶进行非弹性 X 射线散射和衍射实验，评估了 (1) 地震各向异性的来源。 (Mg0.22Fe0.78)O 菱镁矿 (2) 通过对大洋中脊玄武岩相组合进行 X 射线衍射实验来研究地震梯度和不连续性，他们的研究将最终生成 CMB 区域的更新的全球地图。将解决的问题包括：俯冲板片的存在能否使 LLSVP 变形为地震可解析的 3D 形状？富铁 (Mg,Fe)O 是可观测到的地震各向异性的来源，是由俯冲板片附近的地幔流动产生的？这些板片如何相互作用并影响 LLSVP 边缘附近的地​​形和化学特征？