CSEDI: Ultra-High Velocity Zones (UHVZs) at the core-mantle boundary

CSEDI：核幔边界处的超高速带 (UHVZ)

• 批准号: 1855624
• 负责人: Edward Garnero
• 金额: $ 54.48万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-06-01 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1855624&HistoricalAwards=false
• 关键词: CSEDI; Ultra; Velocity; Zones; UHVZs

Nearly half way to the center of the Earth, 2900 km deep, lies the boundary between the rocky mantle and the molten iron-rich outer core. There, at the core-mantle boundary (CMB), small enigmatic structures of tens of km in size were recently observed on the mantle side. The CMB is a critical boundary. The heat conducted away from the core by mantle materials contributes to power the Earth's magnetic field which shields us from the solar wind. Mantle thermal convection, which drives plate tectonics and associated hazards, might have brought unique materials to the CMB; possibly large sections of the Earth's crust and upper mantle. Characterizing the newly observed structures is important, because they hold clues on the planet dynamics, chemical evolution and present-day state. Here, the researchers use seismology - the study of seismic-wave propagation within the Earth - to image and characterize these structures. They are called ultra-high velocity zones, because seismic waves passing through them exhibit remarkably high velocities. To identify their origins, the team studies the convective properties of the mantle using geodynamic modeling. The researchers also carry out experiments and computational calculations to investigate the properties of candidate materials at the extreme pressure and temperature of the deep mantle. These data help to constrain and interpret seismic observations, lifting the veil on the nature of ultra-high velocity zones. This project provides support to an early-career scientist, a postdoctoral associate and two female graduate students. It also promotes training for an undergraduate student and educational outreach to the public at yearly events and via the internet. This multidisciplinary project frames the detection, imaging, modeling, and characterization of ultra-high velocity zones (UHVZs). The team's preliminary work finds them in spots beneath the Cocos and Caribbean tectonic plates, a region located beneath past and present active subduction zones. The researchers focus on mapping and modeling UHVZs there and in other geographical locales, analyzing seismic waves that reflects off of Earth's core (named ScS, ScP, and PcP waves). In addition, they explore compositional possibilities by performing high-pressure experiments and calculations. These involve materials introduced from above, such as subducted ocean crust and sediments, and from below (core-mantle interactions). Experiments on phase relations and properties of minerals are carried out using multi-anvil press and diamond-anvil cell setups at synchrotron national facilities. They explore a large range of pressure, up to the extreme pressure of 135 GPa (~1.3 million atm) prevailing in the lowermost mantle. Experiments are combined with calculations leading to estimates of expected velocities, which are compared with seismological results. In parallel, geodynamic modeling investigates the dynamical behavior of compositional input from subduction or the CMB. This provides a framework guiding the experimental work and the interpretation and modeling of seismic observations. UHVZs may have important effects on a number of deep mantle phenomena, including heat and chemistry exchange between the core and mantle. They may relate to important geodynamical cycles at the origin of the previously documented ultra-low velocity zones and/or thermochemical piles. Investigating the newly discovered CMB structures may provide insights on larger scale processes, like whole mantle convection and the evolution of mantle chemistry.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.

距离地球深2900公里的地球中心的一半是岩石地幔与熔融铁富的外部芯之间的边界。在那里，最近在地幔侧观察到了核心壳边界（CMB）的大小数十亿公里的小神秘结构。 CMB是关键边界。地幔材料从核心远离芯的热量有助于为地球的磁场提供动力，从而使我们免受太阳风的影响。驱动板块构造和相关危害的地幔热对流可能为CMB带来了独特的材料。可能是地壳和上地幔的大部分。表征新观察到的结构很重要，因为它们掌握了行星动力学，化学演化和当今状态的线索。在这里，研究人员使用地震学 - 地球内地震传播的研究 - 图像和表征这些结构。它们被称为超高速度区，因为穿过它们的地震波的速度非常高。为了确定其起源，团队使用地球动力学建模研究地幔的对流特性。研究人员还进行了实验和计算计算，以研究候选材料在深幔的极端压力和温度下的性质。这些数据有助于限制和解释地震观测，从而提高了超高速度区域性质的面纱。该项目为早期的科学家，博士后同学和两名女研究生提供了支持。它还促进了在年度活动和互联网上向公众向公众提供的本科生和教育宣传的培训。 这个多学科项目将超高速区（UHVZS）的检测，成像，建模和表征构成。该团队的初步工作在可可和加勒比海构造板的位置找到了它们，该区域位于过去和现在的主动俯冲带下。研究人员专注于在那里和其他地理环境中进行映射和建模UHVZ，分析反映地球核心（命名为SCS，SCP和PCP波）的地震波。此外，他们通过进行高压实验和计算来探索组成可能性。这些涉及从上方引入的材料，例如俯冲的海角和沉积物，以及下方（核心掩膜相互作用）。有关矿物质的相位关系和矿物质性能的实验，是在同步基金国家设施的多anvil Press和Diamond-Anvil细胞设置进行的。他们探索了巨大的压力，直至最低地幔中占135 GPA（约130万ATM）的极端压力。实验与计算相结合，导致预期速度的估计值，这些速度与地震结果进行了比较。同时，地球动力学建模研究了俯冲或CMB的组成输入的动力学行为。这提供了一个指导实验工作以及地震观察的解释和建模的框架。 UHVZ可能会对许多深陆壁现象具有重要影响，包括核心和地幔之间的热量和化学交换。它们可能与先前记录的超低速度区和/或热化学桩的起源的重要地球动力周期有关。调查新发现的CMB结构可能会提供有关大规模过程的见解，例如整个地幔对流和地幔化学的演变。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛影响的评估标准通过评估来进行评估的。