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Superplumes, superpiles or superpuddings? Understanding the thermochemical dynamics of the mantle with waveform seismology

超级羽、超级桩还是超级布丁？

基本信息

批准号：
NE/K004824/1
负责人：
J Davies
金额：
$ 24.54万
依托单位：
CARDIFF UNIVERSITY
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK004824%2F1
关键词：
Superplumes superpiles superpuddings Understanding thermochemical

项目摘要

We understand plate tectonics. What we still do not understand is how the mantle and plates work together to generate this unique behaviour. This is an outstanding fundamental problem. In particular we do not understand the dynamics of mantle convection including what role composition plays. Seismological studies have shown us that the mantle has two giant mysterious structures at its base, one beneath Africa the other beneath the Pacific. We do not understand their role in mantle convection. There are three hypotheses for these structures, each with different dynamical implications. First that they are the result of thermal convection e.g. result from a cluster of plumes (super-plumes); second that they represent dense detrital pile (super-piles); and third that they are thermo-compositional, resulting from recycling of oceanic crust, leading to distributed heterogeneity (equated by some to plums in a pudding) through the mantle, which maybe more concentrated in these regions (super-puddings). We will produce computer simulations of mantle circulation to investigate each class of hypothesis. We will apply plate motion history to these to produce models that can be compared with the real Earth. Earlier work of our team has shown that both preliminary superplume and superpile models produce structures similar to the two large structures imaged with seismic tomography. The different hypotheses though will have different internal and top structures, which cannot be resolved with current seismic tomography. They can be differentiated seismically, but it requires more advanced methods.This project will bring these more advanced methods to bear. Models of the predicted seismic structure will be produced from the present-day stage of the resulting mantle circulation models. This will be done using a world-class thermodynamic database of the mineralogy and its elastic properties, derived from hundreds of laboratory experiments. The models will be tested using seismic probes that can look inside the structures, and another set that focus at their upper edge. The predictions of the probes for the different hypotheses will be produced by accurately directly simulating the propagating seismic waves. This will be done using the spectral finite-element code SPECFEM3D_GLOBE on the National Supercomputer, HECToR (and soon ARCHER). One set of probes is the so called 'ScS' seismic wave. This is a wave that reflects off the core mantle boundary - this provides a tool to look inside the structure with high lateral resolution. The second set of probes will be body-waves that bottom around the top of the structures. If the structures extend high above the core mantle boundary then waves that only sample them will be affected. The distinctive predicted seismic signatures of the different models will then be compared to the large datasets now available allowing the hypotheses to be exactingly tested. The weak signatures in the data will be amplified by using the advanced techniques of observational seismology of stacking waveforms (adding multiple seismograms), which are best done using arrays of seismometers. They will also provide a good test for current approximate methods used to image and model the mantle structure.The research team has the resources (access to high performance computing), tools (code to model mantle circulation (TERRA, Fluidity) and seismic wave propagation (SPECFEM3D_GLOBE)), data, track record and expertise (including partners for plate motion histories, mineral physics, modelling, and seismic data analysis) in place to undertake this ambitious project.

我们了解板块构造。我们仍然不明白的是地幔和板块如何共同作用以产生这种独特的行为。这是一个突出的根本问题。特别是我们不了解地幔对流的动力学，包括成分所起的作用。地震学研究表明，地幔底部有两个巨大的神秘结构，一个位于非洲下方，另一个位于太平洋下方。我们不了解它们在地幔对流中的作用。这些结构存在三种假设，每种假设都有不同的动力学含义。首先，它们是热对流的结果，例如由一簇羽流（超级羽流）产生；其次，它们代表密集的碎屑堆（超级堆）；第三，它们是热组成的，是由海洋地壳的循环产生的，导致地幔分布的异质性（有些人相当于布丁中的李子），这些异质性可能更集中在这些区域（超级布丁）。我们将对地幔循环进行计算机模拟，以研究每一类假设。我们将应用板块运动历史来生成可以与真实地球进行比较的模型。我们团队的早期工作表明，初步的超级羽流和超级桩模型产生的结构与地震层析成像成像的两个大型结构相似。然而，不同的假设将具有不同的内部和顶部结构，这是当前地震层析成像无法解决的。可以通过地震来区分它们，但这需要更先进的方法。本项目将把这些更先进的方法发挥作用。预测的地震结构模型将从目前阶段的地幔循环模型中产生。这将使用世界一流的矿物学及其弹性特性热力学数据库来完成，该数据库源自数百个实验室实验。这些模型将使用可以观察结构内部的地震探头和另一组聚焦于其上边缘的地震探头进行测试。探测器对不同假设的预测将通过准确地直接模拟传播的地震波来产生。这将使用国家超级计算机 HECToR（以及即将推出的 ARCHER）上的光谱有限元代码 SPECFEM3D_GLOBE 来完成。一组探头是所谓的“ScS”地震波。这是一种从地核边界反射的波——这提供了一种以高横向分辨率观察结构内部的工具。第二组探头将是位于结构顶部周围的体波。如果这些结构延伸到核心地幔边界之上，那么仅对它们进行采样的波就会受到影响。然后，将不同模型的独特预测地震特征与现有的大型数据集进行比较，从而使假设得到精确检验。数据中的弱特征将通过使用叠加波形（添加多个地震图）的观测地震学先进技术来放大，这最好使用地震仪阵列来完成。他们还将为当前用于地幔结构成像和建模的近似方法提供良好的测试。研究团队拥有资源（高性能计算）、工具（地幔循环模型代码（TERRA、Fluidity）和地震波传播（SPECFEM3D_GLOBE））、数据、跟踪记录和专业知识（包括板块运动历史、矿物物理、建模和地震数据分析方面的合作伙伴）来开展这项工作。雄心勃勃的项目。