Finding the missing evidence for Earth's magma ocean: a novel stable isotope approach

寻找地球岩浆海洋缺失的证据：一种新颖的稳定同位素方法

• 批准号: NE/V000411/1
• 负责人: Helen Williams
• 金额: $ 78.67万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 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%2FV000411%2F1
• 关键词: Finding; missing; evidence; Earth; magma

Earth's present belies its violent past. Catastrophic impacts during the Earth's first 500 million years generated enough energy to melt the planet's interior, creating planetary-scale volumes of melt, or "magma oceans". Their subsequent cooling and crystallisation would have set the chemistry of the Earth and its future long-term habitability. However, we do not know exactly where and how the Earth's magma oceans crystallised, what their composition was and whether remnants of early magma ocean material remain present in the Earth's deep interior, potentially acting as important reservoirs for volatiles and precious metals.A key piece of information may reside in the deep Earth: as the magma ocean cooled it would have started to crystallise, with the dense newly formed crystals sinking to the base of Earth's mantle. This would have generated strong chemical layering in the mantle, which could persist to today. This project focuses on finding the chemical evidence for these piles of dense magma ocean crystals, and thus identifying a key missing piece of evidence for Earth's earliest history.As the deepest mantle is inaccessible to direct sampling, we must rely on nature to do this for us. This occurs when regions of the mantle heat up, buoyantly rise and melt, ultimately producing volcanism; a phenomenon exhibited at Iceland, Hawaii and other "mantle plumes". We can use the chemistry of these lavas to probe the composition of the material that melted to form them, thereby gaining a window into the deep Earth. The chemical signals in both modern and ancient lavas have resulted in the paradigm of isolated and "primordial" regions of the Earth's interior, often presumed to be located at the very base of the Earth's mantle, at the boundary with the planet's central metallic core. It has been suggested that the mineralogy and composition of these deep mantle domains has allowed them to resist being entrained into the convecting mantle for billions of years, where they may store volatile- and heat-producing elements. Do these regions of the Earth's mantle have their origin in magma ocean crystallisation? Has magma ocean material always remained isolated from the convecting mantle? Can residual frozen melts or crystalline material left over from magma ocean crystallisation be transported into the upper mantle, and if so, can it melt and contribute to the chemistry of modern and ancient primitive lavas?To answer these questions, we need chemical tracers that, 1) respond directly to the type of minerals that would have formed during the crystallisation of a deep magma ocean, 2) are resistant to alteration when volcanic rocks are weathered at Earth's surface so that they can be applied to ancient lavas, and 3) reflect the bulk properties of the mantle that these lavas were derived from. We propose to use iron (Fe) and calcium (Ca) stable isotopes as tracers. Reconnaissance measurements of 3.7 billion year old rocks shows that these tracers are robust to the rocks' weathering history. The data also contain the tantalising suggestion that these volcanics were derived from melting material residual from a former magma ocean. We will use these tracers to explore the Earth's magma ocean history and its role in defining the chemical and physical state of the planet today. Important steps are:1) Constraining the partitioning of Fe and Ca isotopes during magma ocean crystallisation. We will do this by high-pressure laboratory experiments, where we will simulate the conditions of magma ocean crystallisation and analyse the crystal residues that we produce. 2) Undertaking new Fe and Ca isotope analysis of volcanics ranging from 3.7 billion years old to the present. 3) Develop a series of thermodynamic models to track the Fe and Ca isotope effects of magma ocean crystallisation and to predict the composition of volcanics derived from the entrainment and melting of these magma ocean crystal piles in the upper mantle.

地球现在掩盖了它的暴力过去。地球前5亿年，灾难性的影响产生了足够的能量，以融化地球的内部，从而产生熔体的行星规模，或“岩浆海洋”。他们随后的冷却和结晶将设定地球的化学及其未来的长期宜居性。但是，我们不知道地球的岩浆海洋的何处，是如何结晶的，它们的成分是什么，以及早期的岩浆海洋材料的残留物是否仍然存在于地球内部的深处，可能像重要的挥发物和珍贵金属一样行动，这可能是岩石凉爽的岩石冷却的材料，可以将其与Crystry sum strom confly sum strom confly sumpers starm sumpers confers confers confersy：这将在地幔中产生强大的化学分层，这可能会持续到今天。该项目着重于寻找这些密集的岩浆海洋晶体的化学证据，从而确定了地球最早历史的关键丢失证据。由于最深的地幔无法直接采样，我们必须依靠自然来为我们做到这一点。当地幔地区加热，浮动升起并融化，最终产生火山症时，就会发生这种情况。在冰岛，夏威夷和其他“地幔羽”中表现出的现象。我们可以利用这些熔岩的化学性质来探测融化形成它们的材料的组成，从而获得进入深层的窗户。现代和古代熔岩中的化学信号导致了地球内部孤立和“原始”区域的范式，通常假定位于地球覆盖层的基部，位于地球中央金属核的边界。有人提出，这些深层地幔域的矿物学和成分使他们能够抵抗被夹在对流地幔中的数十亿年，它们可能会存储挥发性和热量产生的元素。地球地幔的这些地区是否起源于岩浆海洋结晶？岩浆海洋材料是否总是与对流地幔隔离？残留的冷冻融化或结晶材料从岩浆海晶的结晶中留下来，将其融化并有助于现代和古代原始熔岩的化学反应并有助于回答这些化学示踪剂，我们需要在磁性播放过程中直接形成的矿物质，即在趋势上播放的矿物质，这是在趋势上播放的，这是远景的2）。地球的表面使它们可以应用于古老的熔岩，3）反映了这些熔岩的堆积性质。我们建议将铁（Fe）和钙（CA）稳定同位素作为示踪剂。 37亿年历史的岩石的侦察测量表明，这些示踪剂对岩石的风化历史具有强大的态度。数据还包含诱人的建议，即这些火山是从以前的岩浆海洋中熔化的材料衍生而来的。我们将使用这些示踪剂来探索地球的岩浆海洋历史及其在定义当今地球的化学和物理状态方面的作用。重要步骤是：1）在岩浆海洋结晶过程中限制Fe和Ca同位素的分配。我们将通过高压实验室实验来做到这一点，在那里我们将模拟岩浆海洋结晶的条件并分析我们产生的晶体残基。 2）对37亿年历史的火山进行新的FE和CA同位素分析。 3）开发一系列热力学模型，以跟踪岩浆海洋结晶的Fe和Ca同位素效应，并预测来自上层岩浆岩浆海洋晶体桩的夹带和熔化的火山的组成。

项目成果

The evolution of the Galápagos mantle plume.

• DOI: 10.1126/sciadv.add5030
• 发表时间: 2023-03-10
• 期刊: Science advances
• 影响因子: 13.6

Global trends in novel stable isotopes in basalts: Theory and observations

玄武岩中新型稳定同位素的全球趋势：理论和观察

• DOI: 10.1016/j.gca.2021.12.008
• 发表时间: 2022
• 期刊: Geochimica et Cosmochimica Acta
• 影响因子: 5
• 作者: Soderman C

Iron isotopes trace primordial magma ocean cumulates melting in Earth's upper mantle.

• DOI: 10.1126/sciadv.abc7394
• 发表时间: 2021-03
• 期刊: Science advances
• 影响因子: 13.6
• 作者: Williams HM;Matthews S;Rizo H;Shorttle O
• 通讯作者: Shorttle O

Iron isotopes trace primordial magma ocean cumulates melting in the Earth's upper mantle

铁同位素追踪地球上地幔中原始岩浆海洋的累积融化

• DOI: 10.17863/cam.66986
• 发表时间: 2021
• 作者: Williams H