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

地幔中物质的行为限制了驱动板块构造的流动。由深地幔源驱动的大量火山爆发被认为导致了全球环境的变化。剧烈的成分和热变化发生在地核-地幔边界（CMB），大约在地球表面以下3000公里。这些变化对地球变冷产生了主要影响。它们还影响地核动力学、地球磁场和地幔热对流。然而，了解地球深处的动力学并非微不足道。的确，需要多学科的努力和最先进的技术来处理地球系统的复杂性。在这里，研究人员研究了在地核-地幔边界观察到的神秘特征。为了揭开它们的起源，该团队结合了地震学、地球动力学和实验矿物物理学的专业知识。研究人员在地幔中普遍存在的极端压力下进行实验。他们在国家同步加速器设施中使用强大的x射线和红外光测量预计存在于下沉到CMB的海洋地壳物质中的物质的性质。利用最新的计算设备，他们模拟了候选海洋地壳物质与深地幔物质的相互作用，这些物质是由地球历史上的构造力聚集在一起的，在深地幔中产生了复杂的结构。这些模型的结果将与地球内部的地震观测结果进行比较，检验我们对地球深部动力学的理解。该项目为加州理工学院的研究生培训提供支持，并促进与澳大利亚的国际合作。地震学家已经揭示，CMB的地幔面是非常不均匀的，具有千米尺度的精细结构，可能包含不同的化学储层。热非均质性和化学非均质性、固固相变、弹性各向异性、可变粘度和熔化可能都是解释观察到的复杂性所必需的。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，该团队通过动力学将原子尺度与构造尺度联系起来，并将其与时间维度联系起来。这是通过测量地球深部相的热弹性特性来完成的，与地震观测到的由地球板块构造历史重建而来的地幔动力学预测的结构相比较。研究人员将对太平洋大低地震速度省（LLSVP）及其近端环境进行系统研究。他们使用完整的地震记录，与增强层析模型和热化学对流模型合成的地震记录进行比较。这些模型整合了受观测约束的板块构造重建，并考虑了材料的物理特性，包括弹性张量和流变特性。实验评估了俯冲板块候选深层含水相地震特征的来源。它们包括：(1)利用非弹性x射线散射技术测量横波速度；(2)利用x射线衍射和同步红外光谱分析下地幔条件下的热状态方程和稳定性约束。该研究解决了一些基本问题，例如：俯冲板块的存在是否会使llsvp变形为具有不同各向异性的地震可分辨的三维形状，并影响D”地形？如果含水相可以被输送到最底部的地幔，它们是否可以通过地震检测到？它们是否在热化学堆的稳定性中发挥作用？这项工作将通过对三名尖端技术研究生的培训来完成，该合作项目将加强与澳大利亚国立大学的伙伴关系。通过地震研究员项目开展的外展活动将包括来自地球科学领域代表性不足的背景的高中生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.