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Investigating Mantle Mixing and Chemical Layering through a Comprehensive Understanding of Transition Zone Seismic Discontinuities

通过全面了解过渡带地震不连续性来研究地幔混合和化学分层

基本信息

批准号：
NE/P001378/1
负责人：
Teh-Ru Alex Song
金额：
$ 50.52万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2016
资助国家：
英国
起止时间：
2016 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FP001378%2F1
关键词：
Investigating Mantle Mixing Chemical Layering

项目摘要

Transition zone seismic discontinuities (TZSDs), manifestations of mineral phase transitions or/and compositional changes between the upper mantle and the lower mantle, hold the key to resolve the mystery of mass and heat transport in the Earth's mantle and the long-term evolution of the Earth's interior.However, seismic characterizations of TZSDs are typically incomplete because of the limit in the data frequency bandwidth and sensitivity relevant to TZSDs. We innovate a simple, effective and high resolution probing of mantle discontinuity through examination of broadband forward and backward scattering waves in the context of the teleseismic receiver function method. This approach will allow us to comprehensively characterize TZSDs beneath the continents, including properties such as discontinuity topography, sharpness and gradient, shear velocity jump and density jump.To date, there has been no single study that is capable of simultaneously determining these essential seismic properties in the TZSDs. These renewed descriptions of TZSDs will be used to explore outstanding questions including mineralogical models of the transition zone and the presence of volatile/melt. In particular, we aim to address how current and past subduction determine short-term and long-term mantle mixing and whether such a mixing process may in turn shape slab sinking dynamics.A series of outstanding questions can be much better addressed with our new seismic observations:Did long-term mixing of billions of years result in apparent chemical layering as indicated in geodynamic models?What are the degree and the length scale of lateral heterogeneity if such a chemical layering exists?Is it possible that primordial structure may survive long term mixing and become trapped in the transition zone?Is the transition zone potentially a relatively shallow reservoir for long-term storage and geochemical evolution of basalt?Does chemical layering or large-scale primordial structure dictate the slab sinking dynamics?Does modern and ancient subduction recycle water into the deep mantle and transition zone?Does hydrated transition zone induce convective instability and contribute to intraplate volcanism?In the proposed work, we will use an innovative and effective observation with broadband forward and backward scattering waves to provide a comprehensive characterization of TZSDs, including properties such as discontinuity topography, sharpness, velocity and density jumps across the boundaries, and the gradient above/below the discontinuities. These unprecedentedly rich observations will provide renewed constraints on fundamental processes relevant to the Earth's interior and evolution.

过渡带地震不连续性（TZSD）是上地幔和下地幔之间矿物相变或/和成分变化的表现，是解决地幔中质量和热量传输以及地球内部长期演化之谜的关键。然而，由于数据频率带宽和数据的限制，TZSD 的地震表征通常是不完整的。与 TZSD 相关的敏感性。我们通过在远震接收函数方法的背景下检查宽带前向和后向散射波，创新了一种简单、有效和高分辨率的地幔不连续性探测方法。这种方法将使我们能够全面表征大陆下方的 TZSD，包括不连续地形、锐度和梯度、剪切速度跳跃和密度跳跃等特性。迄今为止，还没有一项研究能够同时确定 TZSD 中的这些基本地震特性。这些 TZSD 的更新描述将用于探索悬而未决的问题，包括过渡带的矿物学模型和挥发物/熔体的存在。特别是，我们的目标是解决当前和过去的俯冲如何决定短期和长期的地幔混合，以及这种混合过程是否会反过来塑造板片下沉动力学。我们的新地震观测可以更好地解决一系列突出问题：数十亿年的长期混合是否导致了地球动力学模型中所示的明显化学分层？如果存在这种化学分层，横向异质性的程度和长度尺度是多少？原始结构是否有可能在长期混合中幸存下来并被困在过渡带中？过渡带是否可能是玄武岩长期储存和地球化学演化的相对较浅的储层？化学成层或大规模原始结构是否决定了板块下沉动力学？现代和古代俯冲是否将水循环到深部地幔和过渡带中？水合过渡带是否会引起对流不稳定并导致板内火山作用？在拟议的工作中，我们将使用宽带前向和后向散射波的创新且有效的观测来提供 TZSD 的全面表征，包括不连续性地形、清晰度、速度和密度跨边界跳跃以及不连续性上方/下方的梯度等属性。这些前所未有的丰富观测将为与地球内部和演化相关的基本过程提供新的限制。