Collaborative Research: Investigating formation of stagnant slabs and implications for subduction dynamics

合作研究：调查静止板片的形成及其对俯冲动力学的影响

• 批准号: 2244660
• 负责人: Craig Lundstrom
• 金额: $ 33.31万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-02-01 至 2026-01-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2244660&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; formation; stagnant

Many decades have passed since the establishment of the theory of plate tectonics. Scientists still debate how tectonic plates recycling into Earth’s interior evolve over time as they descend. Advances in generating 'seismic tomographic images' of the Earth (analogous to medical CT scans) provide increasingly detailed images of these foundered plates (or 'slabs'), many of which are trapped about 300 to 600 miles below the Earth's surface. These images represent a present-day snapshot of the convecting mantle, and its evolution over time may be investigated through numerical modeling of the subduction process. This collaborative proposal combines recent developments in data-driven modeling and seismic tomography. Liu, Tromp, and their graduate students will explore different ways that subducted slabs get trapped in the mid mantle, with a focus on two competing hypotheses: that the slab is being pulled by one end which is stuck to a plate at the surface, or (2) that it is dragged along with horizontal flow of the surrounding mantle. This research will improve our understanding of how the Earth's mantle flows, and how it has flowed (and how the Earth's plates have moved) over tens of millions of years. Sophisticated software for modeling the slabs and imaging the mantle will be significantly improved and freely shared with other scientists via public websites.Extensive fast seismic anomalies within the 500-1000 km mantle depth range are called stagnant slabs, and their origin has implications for continental tectonics and mantle dynamics. A commonly invoked mechanism is trench retreat, but the observed amount of retreat does not always match simulations. Another frequently made assumption is that slabs sink vertically, even though this can violate geological observations. A potential solution to these problems is to consider lateral mantle flow at mid-mantle depths, whose effect on slab stagnation remains poorly explored. Another complication is the inconsistency of tomographic images of the present-day configuration of stagnant slabs. The PI teams will collaboratively evaluate dynamic effects of trench retreat and lateral mantle flow on slab stagnation by designing 3D spherical Earth models through sequential data assimilation (SDA) and comparing the results with improved tomographic images using full-waveform inversion (FWI) with source encoding. The SDA modeling approach is appropriate for testing key controlling parameters for slab stagnation while simultaneously considering many other natural complexities. The improved FWI method increases seismic resolution significantly at upper-to-mid mantle depths, where stagnant slabs reside. Through a set of SDA models that test the available range of trench motion histories at different geographic locations implemented in both regional- and global-scale simulations, the team will quantify the respective contributions of trench retreat and lateral mantle flow on the formation of observed stagnant slabs. Ultimately, this exercise will generate new insight into subduction dynamics and the associated tectonic records.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.

自从板块构造理论建立以来，已经过去了几十年。科学家们仍在争论地壳板块在下沉过程中是如何在地球内部循环演变的。地球“地震层析成像”技术的进步（类似于医学CT扫描）为这些沉没板块（或“板块”）提供了越来越详细的图像，其中许多板块被困在地球表面以下约300至600英里处。这些图像代表了现今对流地幔的快照，其随时间的演变可以通过俯冲过程的数值模拟来研究。该合作提案结合了数据驱动建模和地震层析成像的最新发展。刘、特朗普和他们的研究生将探索俯冲板块被困在中地幔中的不同方式，重点关注两种相互竞争的假设：板块被粘在表面板块的一端所拉，或者(2)它被周围地幔的水平流动所拖。这项研究将提高我们对地幔如何流动的理解，以及它在数千万年里是如何流动的（以及地球板块是如何移动的）。用于板块建模和地幔成像的复杂软件将得到显著改进，并通过公共网站与其他科学家免费共享。在地幔深度500-1000 km范围内广泛的快速地震异常被称为停滞板块，其起源对大陆构造和地幔动力学具有重要意义。一种常用的机制是堑壕撤退，但观察到的撤退量并不总是与模拟相符。另一个经常被提出的假设是板块垂直下沉，尽管这可能违反地质观测。这些问题的一个潜在解决方案是考虑中地幔深处的横向地幔流动，其对板块停滞的影响尚未得到充分探讨。另一个复杂的问题是现今滞流板形态的层析成像不一致。PI团队将通过顺序数据同化（SDA）设计三维球形地球模型，并将结果与采用全波形反演（FWI）的改进层析成像图像进行比较，共同评估海沟退缩和横向地幔流动对板块停滞的动态影响。SDA建模方法适用于测试板坯停滞的关键控制参数，同时考虑许多其他自然复杂性。改进的FWI方法显著提高了停滞板块所在的上-中地幔深度的地震分辨率。通过一组SDA模型，在区域和全球尺度模拟中测试不同地理位置的海沟运动历史的可用范围，该团队将量化海沟退缩和横向地幔流动对观测到的停滞板块形成的各自贡献。最终，这项工作将对俯冲动力学和相关的构造记录产生新的见解。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。