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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，地幔和板块是如何共同作用来产生这种独特行为的。这是一个突出的根本性问题。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，一个在非洲下面，另一个在太平洋下面。我们不了解它们在地幔对流中的作用。对于这些结构有三种假设，每一种都有不同的动力学含义。第一，它们是热对流的结果，例如来自一簇羽流(超级羽流)；第二，它们代表致密的碎屑堆(超级布丁)；第三，它们是热成分的，源于洋壳的循环，导致地幔中分布的不均一性(有些人相当于布丁中的李子)，可能更集中在这些地区(超级布丁)。我们将制作地幔环流的计算机模拟来研究每一类假说。我们将把板块运动历史应用到这些模型中，以产生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，初步的超烟柱和超堆模型产生的结构与地震层析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，这是目前的地震层析成像无法解决的。它们在地震上是可以区分的，但需要更先进的方法。这个项目将使这些更先进的方法发挥作用。预测的地震结构模型将从所产生的地幔环流模型的当前阶段产生。这将使用世界级的矿物学热力学数据库及其弹性性质来完成，该数据库来自数百个实验室实验。这些模型将使用地震探头进行测试，这些探头可以观察结构内部，另一组探头聚焦在结构的上缘。通过准确地直接模拟地震波的传播，将产生对不同假设的探头的预测。这将使用国家超级计算机赫克托(很快还会是阿彻)上的频谱有限元程序SPECFEM3D_GLOBLE来完成。其中一组探头是所谓的“SCS”地震波。这是一种反射出核心地幔边界的波--这提供了一种以高横向分辨率观察结构内部的工具。第二组探测器将是围绕结构顶部底部的体波。如果这些结构延伸到地核地幔边界以上的高度，那么只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的检验。数据中的微弱特征将通过使用先进的观测地震学叠加波形(添加多个地震图)技术来放大，这最好是使用地震仪阵列来完成。他们还将对目前用于成像和模拟地幔结构的近似方法进行良好的测试。研究团队拥有资源(获得高性能计算)、工具(模拟地幔环流(Terra、流动性)和地震波传播的代码(SPECFEM3D_Globe))、数据、跟踪记录和专业知识(包括板块运动史、矿物物理、建模和地震数据分析的合作伙伴)来实施这一雄心勃勃的项目。