Oxygen fugacity in a heterogeneous mantle: Earth's deep oxygen cycle

异质地幔中的氧逸度：地球深部氧循环

基本信息

批准号：
NE/T011106/1
负责人：
David Neave
金额：
$ 85.66万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2021
资助国家：
英国
起止时间：
2021 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FT011106%2F1
关键词：
Oxygen fugacity heterogeneous mantle Earth

项目摘要

Is it a coincidence that Earth is the only planet on which both life and plate tectonics are known to exist? This is the fundamental question that motivates my future research vision. As plate tectonic theory has matured over the past 50 years, we have come to increasingly appreciate our planet's dynamism and complexity. Tectonic subduction of oceanic lithosphere over billions of years has played a central role in creating the compositional heterogeneity we now see reflected in the chemical variability of magmas erupted at mid-ocean ridges and ocean islands. Hydrothermal circulation at mid-ocean ridges oxidises newly formed lithosphere, meaning that subduction transports oxygen from Earth's surface into its deep interior, generating variability in mantle oxygen contents. However, current observations from erupted magmas, which offer windows into Earth's deep chemical structure, provide conflicting views on whether subduction has created heterogeneity in the oxidising potential (i.e. oxygen fugacity; fO2) of the mantle alongside variations in oxygen content. Moreover, current approaches for estimating magma fO2 are often subject to considerable uncertainties and can rarely be applied to the near-primary magmas that record the most information about compositional and fO2 heterogeneity at depth. Thus, the extent to which variations in mantle fO2 are coupled to the tectonically driven deep oxygen cycle remains largely unknown despite the fact that the fO2 of the volcanic gases that mediate long-term planetary habitability is ultimately determined by the fO2 of erupted magmas and their mantle sources.Outstanding problems impeding our ability to determine whether mantle fO2 is coupled to the deep oxygen cycle and holistically evaluate the deep Earth's role in creating a habitable planet include:- Does the subduction of oceanic lithosphere create fO2 heterogeneity in the convecting mantle?- Did the onset of subduction (i.e. plate tectonics) change the fO2 or fO2 structure of the mantle?- Did changes in the fO2 or fO2 structure of the mantle over geological time play a role in creating the oxidising atmosphere upon which much of Earth's current life depends?This NERC IRF aims to resolve the first of these problems by determining whether the subduction of oceanic lithosphere creates fO2 heterogeneity in the convecting mantle. I will achieve this by exploiting the fO2-sensitive speciation of Fe (i.e. Fe3+/FeT) in clinopyroxene to provide a step change in our ability estimate the fO2 of magmas and their mantle sources by addressing four questions:Q1 How does clinopyroxene Fe3+/FeT in magmas relate to mantle source composition?Q2 How does clinopyroxene Fe3+/FeT record fO2 during magmatic evolution in the crust?Q3 How do fO2 and mantle composition independently affect melt Fe3+/FeT during melting?Q4 To what extent is mantle fO2 coupled to Earth's tectonically driven deep oxygen cycle?I will answer these questions by combining high-pressure, high-temperature experiments with cutting-edge X-ray absorption near edge structure (XANES) spectroscopy to determine and then model the fO2 dependence of Fe3+/FeT in magmatic and mantle clinopyroxenes in unprecedented detail. I will calibrate new clinopyroxene-based tools for estimating magma fO2 and apply them to mid-ocean ridge, ocean island and volcanic arc magmas derived from mantle sources containing different amounts of subducted oceanic lithosphere. I will then relate the melt Fe3+/FeT of these magmas to the fO2 of their mantle sources using newly calibrated fO2-sensitive melting models. I will thus provide new insights into the fO2 of the subduction zone outputs that feed both arc and ocean island magmatism. Furthermore, developing the tools required to investigate fO2 heterogeneity in the present mantle will help me to pursue my future research vision of understanding how subduction has shaped Earth's ability to support life through geological time.

地球是唯一已知存在生命和板块构造的行星的巧合吗？这是激发我未来研究愿景的基本问题。随着板块构造理论在过去的50年中成熟，我们越来越欣赏地球的活力和复杂性。数十亿年来，海洋岩石圈的构造俯冲在创造组成异质性方面发挥了核心作用，我们现在看到在中山山脊和海洋岛的岩浆的化学变异性中反映出。海脊中的水热循环氧化新形成的岩石圈，这意味着俯冲将氧气从地球表面传递到其深内部，从而产生地幔氧含量的变异性。然而，当前来自爆发的岩浆的观察结果为地球深层化学结构提供了窗户，对俯冲是否在氧化电位（即氧气散发性; fo2; fo2）的异质性方面提供了矛盾的看法。此外，当前估计岩浆FO2的方法通常会受到相当大的不确定性的影响，并且很少能应用于近乎主要的岩浆，这些岩浆记录了有关深度构图和FO2异质性的最多信息。因此，尽管介导长期行星可居住的火山气体的FO2最终由爆发的岩浆及其能力的fo2确定，但在构造长期行星的fo2中最终确定了介导的fo2，但在大量的问题上确定了在爆发的循环中，确定了山地的问题，是否构成了逐渐的问题。整体上评估地球在创造一个可居住的星球中的作用包括： - 海洋岩石层的俯冲在对流地幔中会产生FO2异质性吗？地球当前的大部分生命都依赖于哪个？这种NERC IRF旨在通过确定海洋岩石圈的俯冲是否在对流地幔中产生FO2异质性来解决这些问题的第一个问题。我将通过利用Clinopyroxene中Fe（即Fe3+/FET）的FO2敏感形式来实现这一目标，以在我们的能力上提供一步的变化，以估计岩浆的FO2及其地幔来源，通过解决四个问题：Q1：Q1 Clinopyroxene Fe3+fe3+agmas在MAGMAS中如何与Qu Magmate fe3+fef3+fef3+cline fe3+cline fe3+clinopy fe3+clinepopy fe3+cline fe3+clinepopy fe3+clinepopy fe3+clinepoy fef3+3 c3 Q3 FO2和地幔成分如何独立影响熔融融化过程中的熔体Fe3+/FET？Q4在多大程度上与地球上的地幔FO2与地球构造驱动的深层氧气周期耦合在一起？我将通过将高压，高度的实验与高级X-RAY吸收结构结合（X-Ray fosy）（x-Ray fosy）（Xanans）（Xanans）（Xanans）的高压效果（Xanan）来回答这些问题？ Fe3+/FET在前所未有的细节中，在岩浆和地幔斜角中。我将校准新的基于Clinopyroxene的工具，用于估算岩浆FO2，并将其应用于源自包含不同量的俯冲海洋岩石圈的地幔源的海岛和火山弧岩浆中。然后，我将使用新校准的FO2敏感熔融模型将这些岩浆的熔体Fe3+/FET与其地幔源的FO2联系起来。因此，我将对俯冲带的FO2提供新的见解，这些俯冲带的输出均可供应弧和海洋岛岩浆。此外，开发在当前地幔中研究FO2异质性所需的工具将帮助我追求我未来的研究愿景，以了解俯冲如何塑造地球通过地质时代来维持生命的能力。