Magmatic volatiles in the fourth dimension

第四维度的岩浆挥发物

• 批准号: NE/X013642/1
• 负责人: Margaret Hartley
• 金额: $ 102.88万
• 依托单位: University of Manchester
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX013642%2F1
• 关键词: Magmatic; volatiles; fourth; dimension

Volcanoes release large quantities of magmatic gases such as water, carbon dioxide and sulfur dioxide into the oceans and atmosphere. The volatile elements that make up these gases are stored in the Earth's mantle, and are released by partial melting of mantle rocks. Volatile elements are cycled between the Earth's surface and its interior by plate tectonics. At subduction zones, rocks from the sea floor re-enter the deep interior of the Earth, carrying with them volatile elements like carbon, sulfur, and halogens (F, Cl, Br and I). Over millions of years, this process has created considerable variability in the distribution of volatile elements in the mantle, and this in turn controls the budgets and fluxes of volatiles that impact the Earth's surface environments in modern-day volcanic eruptions: magmas with high volatile contents tend to produce more explosive and dangerous eruptions, while volcanic gas emissions pose health hazards to regional populations. While magma volatile contents are intrinsically linked to the composition of the mantle sources that supply them, the processes that control the volatile inventories of distinctive mantle sources remain uncertain. Understanding the origin and change over time of the volatile composition of the deep Earth is a fundamental challenge in the Earth Sciences.In this project we aim to discover the volatile signatures and inventories of the distinctive mantle sources that feed major basaltic eruptions. To do this, we will study the volatile contents of silicate melt inclusions, which are tiny pockets of magma trapped in growing volcanic minerals that preserve the dissolved gas content of the magma before it erupts to the surface.First, we will benchmark the volatile inventories of three distinctive mantle types. We have selected two samples from Iceland that represent deep and shallow mantle sources, and one sample from the Canary Islands that represents a subduction-recycled mantle component. We will focus on the halogens, which are sensitive geochemical tracers of recycled material in the mantle. We aim to derive a quantitative understanding of the mechanisms and processes by which volatiles are recycled into the mantle.Second, we will develop new 3D imaging and spectroscopy techniques to fully quantify the volatile contents of melt inclusions. We will use this information to accurately reconstruct magma volatile budgets and provide new information central to quantifying the geological water and carbon cycles.Third, we will apply our new analytical approaches to melt inclusions from the recent eruptions of Fagradalsfjall (Iceland, Mar-Sep 2021) and Cumbre Vieja (La Palma, Sep-Dec 2021). Both these eruptions showed astonishing time-dependent geochemical variability in their erupted magma compositions and gas fluxes. We aim to link temporal changes in magma volatile geochemistry with gas fluxes measured by ground-based sensors and from satellites, to test whether temporal changes in volcanic gas emissions are ultimately controlled by differential melting and sampling of heterogeneous mantle reservoirs.This work will deliver new insights into mantle heterogeneity and volatile geochemical cycling, and will feed into ongoing efforts to develop volatile proxies to predict eruption onset and cessation in volcanically active regions.

火山向海洋和大气中释放大量的岩浆气体，如水、二氧化碳和二氧化硫。构成这些气体的挥发性元素储存在地幔中，并通过地幔岩石的部分熔融而释放出来。挥发性元素通过板块构造在地球表面和内部之间循环。在俯冲带，来自海底的岩石重新进入地球内部深处，携带着挥发性元素，如碳，硫和卤素（F，Cl，Br和I）。数百万年来，这一过程使地幔中挥发性元素的分布产生了相当大的变化，而这反过来又控制了在现代火山爆发中影响地球表面环境的挥发物的收支和流量：挥发性含量高的岩浆往往会产生更具爆炸性和危险性的喷发，而火山气体排放则对区域人口构成健康危害。虽然岩浆挥发性成分与供应它们的地幔源的组成有内在联系，但控制独特地幔源挥发性库存的过程仍然不确定。了解地球深部挥发性成分的起源和随时间的变化是地球科学的一个基本挑战。在这个项目中，我们的目标是发现供给主要玄武岩喷发的独特地幔源的挥发性特征和库存。为此，我们将研究硅酸盐熔体包裹体的挥发性成分。硅酸盐熔体包裹体是被不断生长的火山矿物质所捕获的岩浆的小口袋，在岩浆喷发到地表之前，它保存了岩浆中溶解的气体成分。首先，我们将对三种不同地幔类型的挥发性物质清单进行基准测试。我们从冰岛选择了两个代表深地幔和浅地幔来源的样品，从加那利群岛选择了一个代表俯冲-再循环地幔成分的样品。我们将重点讨论卤素，这是地幔中再循环物质的敏感地球化学示踪剂。我们的目标是获得挥发分再循环到地幔的机制和过程的定量理解。其次，我们将开发新的三维成像和光谱技术，以充分量化熔融包裹体的挥发分含量。我们将利用这些信息准确重建岩浆挥发性预算，并为量化地质水和碳循环提供新的核心信息。第三，我们将应用我们的新分析方法分析最近Fagradalsfjall（冰岛，2021年3月至9月）和Cumbre Vieja（拉帕尔马，2021年9月至12月）火山爆发的熔融包裹体。这两次喷发都显示出惊人的随时间变化的地球化学变化，在其喷发的岩浆成分和气体通量。我们的目标是将岩浆挥发性地球化学的时间变化与地面传感器和卫星测量的气体通量联系起来，以测试火山气体排放的时间变化是否最终受到异质地幔储层的差异熔融和取样的控制。这项工作将为地幔异质性和挥发性地球化学循环提供新的见解，并将为正在进行的开发不稳定代用指标以预测火山活跃地区喷发开始和停止的努力提供投入。