CSEDI: Integrated seismic, geodynamic, and mineral physics studies of multi-scale structures in the lowermost mantle

CSEDI：最下地幔多尺度结构的地震、地球动力学和矿物物理综合研究

• 批准号: 2009935
• 负责人: Jennifer Jackson
• 金额: $ 36.4万
• 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: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2009935&HistoricalAwards=false
• 关键词: CSEDI; Integrated; seismic; geodynamic; mineral

The behavior of materials in the deep Earth constrains the flows that drive plate tectonics. Voluminous eruptions driven by deep mantle sources are thought to have caused global environmental changes. At the core-mantle boundary (CMB) – about 3000 km below the Earth’s surface - dramatic compositional and thermal changes occur. These changes exert a primary influence on the cooling of the planet. They also influence the core dynamics (hence Earth’s magnetic field) and impact 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 combine 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 deep Earth materials using powerful x rays and infrared light at national synchrotron facilities. Taking advantage of recent advances in computational facilities, they simulate the interaction of crustal materials with lower-mantle materials made of multi-scale structures. These materials are brought together by tectonic forces through Earth’s complex history. Outputs of the models are compared with seismic observations, hence gradually unveiling the dynamics of the deep Earth. The project provides support for graduate students at the California Institute of Technology. It also fosters international collaboration with Australia and the UK. 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 (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). The researchers conduct a systematic study of the Pacific large low seismic velocity province (LLSVP) and proximal surroundings such as ultralow velocity zones (ULVZs). 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. 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 3D shapes (with distinctive anisotropy) and affects D" topography and chemically–distinct structures near the edges of LLSVPs? Are all ULVZs created equally? If hydrous phases can be transported into the lowermost mantle, are they seismically detectable and can they contribute to the stability of a thermo-chemical pile?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.

地球深处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喷发导致了地核-地幔边界（CMB）（距地球表面约 3000 公里）的变化。发生剧烈的成分和热变化。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（因此是地球磁场）并影响地幔热对流。事实上，解决地球系统的复杂性需要多学科的努力和最先进的技术，研究人员研究了在地核-地幔边界观察到的神秘特征。该团队结合了地震学、地球动力学和实验矿物物理学方面的专业知识，在地幔中普遍存在的极端压力下进行了实验，他们利用强大的 X 射线和红外光测量了地球深处的物质特性。他们利用计算设施的最新进展，模拟了地壳材料与由多尺度结构构成的下地幔材料的相互作用，并通过地球的复杂历史将这些材料聚集在一起。地震观测，从而逐步揭示地球深处的动力学，该项目为加州理工学院的研究生提供了支持，它还促进了与澳大利亚和英国地震学家的国际合作。宇宙微波背景具有极其不均匀的性质，具有公里级的精细结构，可能具有独特的化学非均质性、固-固相变、弹性各向异性、可变粘度和熔化，这些可能都是解释所观察到的复杂性所必需的。通过地震学、地球动力学和实验矿物物理学，该团队将原子尺度（地球深处相的热弹性特性）与构造尺度（地震观测到的结构及其动力学）联系起来，将所有过程与时间维度联系起来（构造板块历史的重建）研究人员对太平洋大低地震速度区（LLSVP）和超低速区（ULVZ）等邻近地区进行了系统研究。他们使用完整的地震图进行比较。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。俯冲板片中候选深层含水相的地震特征包括：（1）使用非弹性 X 射线散射技术测量剪切波速度；（2）使用 X 射线衍射和同步加速器红外技术进行状态热方程和稳定性约束。这项研究解决了一些基本问题，例如：俯冲板片的存在能否使 LLSVP 变形为地震可解析的 3D 形状（具有独特的特征）。各向异性）并影响 LLSVP 边缘附近的 D" 地形和化学上不同的结构？所有 ULVZ 的创建都是平等的吗？如果含水相可以输送到最下地幔，它们是否可以通过地震探测到，是否有助于热稳定化学堆？该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Inferring material properties of the lower mantle minerals using Mixture Density Networks

使用混合密度网络推断下地幔矿物的材料特性

• DOI: 10.1016/j.pepi.2021.106784
• 发表时间: 2021-10-01
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: Ashim Rijal;L. Cobden;J. Trampert;J. Jackson;A. Valentine
• 通讯作者: A. Valentine

Small‐Scale Intraslab Heterogeneity Weakens Into the Mantle Transition Zone

小尺度板内异质性减弱到地幔过渡带

• DOI: 10.1029/2021gl094470
• 发表时间: 2021-11
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Shen, Zhichao;Zhan, Zhongwen;Jackson, Jennifer M.
• 通讯作者: Jackson, Jennifer M.

Dynamics of the abrupt change in Pacific Plate motion around 50 million years ago

5000万年前太平洋板块运动突变的动力学

• DOI: 10.1038/s41561-021-00862-6
• 发表时间: 2021-12-23
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: Jiashun Hu;M. Gurnis;J. Rudi;G. Stadler;R. Müller
• 通讯作者: R. Müller

Shear properties of MgO inferred using neural networks

使用神经网络推断 MgO 的剪切特性

• DOI: 10.5194/ejm-35-45-2023
• 发表时间: 2023-01-17
• 期刊: European Journal of Mineralogy
• 影响因子: 2.1
• 作者: Ashim Rijal;L. Cobden;J. Trampert;H. Marquardt;J. Jackson
• 通讯作者: J. Jackson

The influence of δ-(Al,Fe)OOH on seismic heterogeneities in Earth’s lower mantle

δ-(Al,Fe)OOH 对地球下地幔地震异质性的影响

• DOI: 10.1038/s41598-021-91180-9
• 发表时间: 2021-06-08
• 期刊: Scientific Reports
• 影响因子: 4.6
• 作者: I. Ohira;J. Jackson;W. Sturhahn;G. Finkelstein;T. Kawazoe;T. Toellner;A. Suzuki;E. Ohtani
• 通讯作者: E. Ohtani