Phanerozoic palaeomagnetic variations and their implications for the Earth's deep interior

该项目将描述和模拟过去5亿年地球磁场的长期变化，以解决有关地球深部动力学和演化的三个主要争议：地球最下层地幔中大型地震异常结构的流动性，地球内核的年龄，以及长期古地磁变化的性质和原因。地磁场是由地球外核的地球发电机过程产生的，是地球的基本属性。它保护大气和生命不受有害太阳风辐射的影响，并提供了一扇通往地球深处的窗口，通过古地磁记录，它具有独特的地球物理能力，可以追溯到地质时代。人们普遍认为，地球磁场的长期变化（超过1000万年）反映了地核-地幔演化对地球动力学的影响，因此可以为人们知之甚少的地球深部过程提供急需的观测约束。特别是，它们可以帮助解决一个重大的悬而未决的争议，即关于地球下地幔中大型结构的流动性，一些人认为这是静态的、长期存在的“热化学堆”，它决定了地球表面板块构造的性质，但另一些人则认为这是短暂的“超级羽流”，是对地表主导过程的反应。它们还有助于解决关于地球内核年龄的重大争议；在这个主题上，集结的研究小组成员最近在领先的多学科杂志《自然》上发表了相互矛盾的结果（相差大约10亿年）。我们团队之前的工作集中在前寒武纪（超过5.4亿年）的古地磁变化和核幔演化上。现在，通过关注过去5亿年，我们可以直接解决上述争议和更广泛的问题，即究竟是什么控制了长期的磁场变化。为了做到这一点，我们需要回答一些基本问题：1。古地磁变化是否如当前记录所暗示的那样是周期性的（周期约为2亿年）？古磁场行为的所有方面（极性反转频率、磁场强度和短期方向变化）是否以可预测的方式同时变化？3. 3 .大型下地幔结构不同程度的活动性如何影响古地磁行为（例如，以循环方式和/或古地磁行为的所有不同方面同时发生变化？）？在过去的5亿年里，我们如何期望不同的内核年龄在古地磁行为中表现出来？在这个项目中，我们将首先使用新的测量和最近发表的分析技术来回答问题1和2，并建立过去5亿年古地磁变化的描述，其质量和实用性是前所未有的。为了回答问题3和4，我们还将根据不同核幔演化情景下的地球动力学数值模型生成古地磁变化的合成记录。通过比较和对比新的观测和合成记录，我们将能够确定哪种情景是最现实的（静态热化学堆还是移动超羽流？）年轻的还是年老的内核？)，以解决突出的争议，并朝着一个完全整合的核-地幔演化模型，包括地球磁场。

This project will describe and model long term variations in Earth's magnetic field through the last 500 million years in order to address three major linked controversies regarding the dynamics and evolution of Earth's deep interior: the mobility of large seismically anomalous structures in Earth's lowermost mantle, the age of Earth's inner core, and the nature and causes long-term palaeomagnetic variations. The geomagnetic field, generated in Earth's outer core by the geodynamo process, is a fundamental property of the planet. It shields the atmosphere and life from harmful solar wind radiation and provides a window to the deep interior of the planet which, through palaeomagnetic records, has the unique geophysical capability of being extended back through geological time. Long term variations in Earth's magnetic field (more than 10 million years) are widely thought to reflect the influence of core-mantle evolution on the geodynamo and therefore could provide badly-needed observational constraints on poorly understood deep Earth processes. In particular, they could help resolve a major outstanding controversy concerning the mobility of large structures in the Earth's lower mantle which are argued by some to be static long-lived "thermochemical piles" that dictate the nature of plate tectonics at Earth's surface, but by others to be transient "superplumes" forming in response to surface-dominated processes. They could also help to resolve a major outstanding controversy concerning the age of Earth's inner core; a topic on which members of the assembled research team have recently published conflicting results (differing by approximately 1 billion years) in the leading multidisciplinary journal, Nature. Previous work by our team has focused on palaeomagnetic variations and core-mantle evolution in the Precambrian (older than 540 million years). Now we are in a position to directly address both of the above controversies and the broader question of what, precisely, controls the long term magnetic variations, by focusing on the last 500 million years. In order to do this, we need to answer some fundamental questions:1. Are palaeomagnetic variations cyclic (with a period of ca. 200 million years) as current records hint?2. Do all aspects of palaeomagnetic field behaviour (polarity reversal frequency, field strength, and short-term directional variability) vary simultaneously in a predictable way? 3. How would we expect different degrees of mobility of the large lower mantle structures to affect palaeomagnetic behaviour (E.G. In a cyclic way way and/or with all the different aspects of palaeomagnetic field behaviour changing simultaneously?)?4. How would we expect different inner core ages to manifest themselves in palaeomagnetic behaviour over the last 500 million years?In this project, we will firstly use new measurements and recently published analysis techniques to answer questions 1 and 2 and build a description of palaeomagnetic variations in the last 500 million years that is unprecedented in its quality and usefulness. To answer questions 3 and 4, we will also produce synthetic records of palaeomagnetic variations from numerical models of the geodynamo subject to different core-mantle evolution scenarios. By comparing and contrasting the new observational and synthetic records, we will then be in a position to determine which scenarios are the most realistic (static thermochemical piles or mobile superplumes? Young or old inner core?), to address the outstanding controversies, and to move towards a fully integrated model of core-mantle evolution incorporating the Earth's magnetic field.