CSEDI: Integrated seismic, geodynamic, and mineral physics studies of scatterers and other multi-scale structures in Earth’s lower mantle

CSEDI：地球下地幔散射体和其他多尺度结构的综合地震、地球动力学和矿物物理研究

• 批准号: 2303148
• 负责人: Jennifer Jackson
• 金额: $ 63.97万
• 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: 2023
• 资助国家: 美国
• 起止时间: 2023-06-15 至 2026-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2303148&HistoricalAwards=false
• 关键词: CSEDI; Integrated; seismic; geodynamic; mineral

The behavior of materials in the Earth’s mantle constrains the flows that drive plate tectonics. Voluminous volcanic eruptions driven by deep mantle sources are thought to have caused global environmental changes. Dramatic compositional and thermal changes occur at the core-mantle boundary (CMB), about 3000 km below the Earth’s surface. These changes exert a primary influence on the cooling of the planet. They also influence the core dynamics, the Earth’s magnetic field, and mantle thermal convection. Yet, understanding the dynamics of the deep Earth is not trivial. Indeed, multidisciplinary efforts and state-of-the art techniques are required to tackle the complexity of the Earth system. Here, the researchers investigate enigmatic features observed at the core-mantle boundary. To unveil their origin, the team combines expertise in seismology, geodynamics, and experimental mineral physics. The researchers carry out experiments at the extreme pressures prevailing in the mantle. They measure the properties of materials anticipated to exist in of oceanic crustal material sinking to the CMB using powerful x-rays and infrared light at national synchrotron facilities. Taking advantage of recent advances in computational facilities, they simulate the interaction of candidate oceanic crustal materials with deep-mantle materials brought together by tectonic forces acting throughout Earth’s history to produce complex structures in the deep mantle. The results of the models will be compared with seismic observations of the Earth’s interior, testing our understanding of the dynamics of the deep Earth. The project provides support for the training of graduate students at the California Institute of Technology and fosters international collaboration with Australia. 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 the observed complexity. With expertise in seismology, geodynamics and experimental mineral physics, the team connects the atomic scale to the tectonic scale as linked to the temporal dimension through dynamics. This is accomplished through the measurement of the thermoelastic properties of deep Earth phases as compared to seismically observed structures predicted by mantle dynamics arising from reconstructions of Earth’s plate tectonic history. The researchers will conduct a systematic study of the Pacific large low seismic velocity province (LLSVP) and proximal surroundings. They use whole seismograms compared against synthetics generated from enhanced tomographic models and thermo-chemical convection models. The models integrate plate tectonic reconstructions constrained by observations and account for materials’ physical properties, including elastic tensors and rheological properties. The experiments assess the sources of the seismic signatures of candidate deep hydrous phases in subducted slab. They include: (1) shear-wave speed measurements using inelastic x-ray scattering techniques; and (2) thermal equation of state and stability constraints using x-ray diffraction and synchrotron infrared spectroscopy at lower mantle conditions. The study addresses fundamental questions, such as: can the presence of subducted slabs deform LLSVPs into seismically resolvable 3-D shapes with distinctive anisotropy and affect D" topography? If hydrous phases can be transported into the lowermost mantle, are they seismically detectable and do they play a role in the stability of a thermo-chemical pile? This work will be accomplished through the training of three graduate students in cutting-edge techniques, and the collaborative project will enhance partnerships with Australian National University. Outreach activities through the Earthquake Fellows Program will include high school students from backgrounds underrepresented in the geosciences.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.

地幔中物质的行为限制了驱动板块构造的流动。据认为，由深部地幔源驱动的大量火山喷发导致了全球环境的变化。在地核-地幔边界（CMB）处发生了剧烈的成分和热变化。在地球表面以下 3000 公里处，这些变化对地球的冷却产生主要影响，它们还影响地核动力学、地球磁场和地幔热。然而，了解地球深处的动力学并非易事，需要多学科的努力和最先进的技术来解决地球系统的复杂性。为了揭示它们的起源，研究小组结合了地震学、地球动力学和实验矿物物理学的专业知识，他们在地幔中普遍存在的极端压力下进行了实验，测量了预计存在于海洋地壳中的物质的特性。他们利用国家同步加速器设施中的强大 X 射线和红外光，模拟了沉入 CMB 的物质，利用计算设施的最新进展，模拟了候选海洋地壳物质与在整个地球历史中作用的构造力聚集在一起的深部地幔物质的相互作用。模型的结果将与地球内部的地震观测进行比较，测试我们对地球深层动力学的理解，该项目为研究生的培训提供支持。加州理工学院和促进与澳大利亚的国际合作揭示了宇宙微波背景的地幔一侧非常不均匀，具有公里级的精细结构，可能蕴藏着独特的化学储层、固-固相变。弹性各向异性、可变粘度和熔化可能都是解释所观察到的复杂性所必需的，该团队凭借地震学、地球动力学和实验矿物物理学方面的专业知识，将原子尺度与物理尺度联系起来。通过与地球板块构造历史重建所产生的地幔动力学预测的地震观测结构相比，通过测量深部地球阶段的热弹性特性来实现构造尺度。他们使用完整的地震图与增强型层析成像模型和热化学对流模型生成的合成图进行研究。受观测限制的构造重建并考虑了材料的物理特性，包括弹性张量和流变特性，这些实验评估了俯冲板片中候选深层含水相的地震特征源，其中包括：（1）使用剪切波速度测量。非弹性 X 射线散射技术；(2) 在下地幔条件下使用 X 射线衍射和同步加速器红外光谱的热状态方程和稳定性约束。例如：俯冲板片的存在能否使 LLSVP 变形为具有独特各向异性的地震可解析 3D 形状并影响 D" 地形？如果含水相可以输送到最下地幔中，它们是否可以通过地震检测到，并且在稳定性中发挥作用吗？这项工作将通过对三名研究生进行尖端技术培训来完成，该合作项目将通过地震活动加强与澳大利亚国立大学的合作伙伴关系。研究员计划将包括来自地球科学领域代表性不足的高中生。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。