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/K004875/1
负责人：
James Wookey
金额：
$ 22.66万
依托单位：
University of Bristol
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%2FK004875%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盘子如何共同努力以产生这种独特的行为。这是一个重大的基本问题。特别是我们不了解地幔对流的动力学，包括角色组成的扮演。地震学研究表明，地幔在其基础上有两个巨大的神秘结构，一个在非洲下方，另一个在太平洋之下。我们不了解它们在地幔对流中的作用。这些结构有三个假设，每个假设都有不同的动力学意义。首先，它们是热对流的结果由一群羽毛（超羽）产生；其次，它们代表着密集的碎屑桩（超托架）；第三，它们是由海壳的回收，导致分布的异质性（由某些人等同于布丁中的李子等同）引起的热组合，这可能会在这些地区（超级繁殖）更加集中。我们将对地幔循环的计算机模拟进行研究，以研究每类假设。我们将将板运动历史记录应用到这些模型中，以与真实的地球进行比较。我们团队的较早工作表明，初步的超级胶合物和超级底线模型都产生了类似于用地震层析成像成像的两个大型结构的结构。尽管不同的假设将具有不同的内部和顶级结构，而目前的地震层析成像无法解决。它们可以在地震上进行区分，但需要更高级的方法。该项目将带来这些更高级的方法。预测的地震结构的模型将从最终的地幔循环模型的当今阶段产生。这将使用矿物学及其弹性特性的世界一流的热力学数据库来完成，该数据库来自数百个实验室实验。这些模型将使用可以看见结构内部的地震探针进行测试，而另一组集则集中在其上边缘。通过准确模拟传播的地震波的准确模拟，将产生对不同假设的探针的预测。这将使用频谱有限元代码Specfem3D_Globe在国家超级计算机Hector（和Suon Archer）上完成。一组探针是所谓的“ SCS”地震波。这是一个反射核心地幔边界的波浪 - 这提供了一种工具，可以用高横向分辨率来看结构内部。第二组探针将是围绕结构顶部底部的身体波。如果结构在核心地幔边界上方延伸高，则仅将其采样的波就会受到影响。然后将将不同模型的独特预测震荡特征与现在可用的大型数据集进行比较，从而可以对假设进行精确检验。通过使用堆叠波形（添加多个地震图）的高级观察性地震学技术（最好使用地震仪阵列完成），将扩大数据中的弱标志。 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雄心勃勃的项目。