Magma mush eruptibility: the lifetime of mobile magma

岩浆糊喷发性：移动岩浆的寿命

基本信息

批准号：
NE/T000430/1
负责人：
Madeleine Humphreys
金额：
$ 64.44万
依托单位：
Durham University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2020
资助国家：
英国
起止时间：
2020 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FT000430%2F1
关键词：
Magma mush eruptibility lifetime mobile

项目摘要

Volcanism - the generation and eruption of molten rock from within the earth's interior - is one of the most visible manifestations of plate tectonics. Growth of the earth's crust occurs either when magma is stored and solidified within the crust, or is erupted at the earth's surface. Eruptive activity at subduction zones can be explosive and highly disruptive, and represents an important natural hazard, with implications for life, health and financial stability when it occurs. One of the major challenges facing volcanologists is the accurate forecasting of this eruptive behaviour. Abundant evidence of past volcanic activity shows that large volumes of magma can be erupted in a single event. However, geophysical techniques used to image below the earth's surface fail to distinguish large volumes of melt (magmatic liquid) stored within the crust. Instead, melt may be stored as "crystal mush", i.e. an accumulation of volcanic crystals separated by only small amounts of melt that is hard to image geophysically. However, a crystal mush with low melt content behaves like a solid and cannot be erupted. Researchers therefore suggest that the mush contains 'eruptible' lenses that have higher melt content, yet remain thin enough to be unresolved by geophysical techniques. If so, then wholesale spatial reorganisation of crystals and liquid in the whole mushy region could change its overall physical behaviour, such that it quickly becomes eruptible. In contrast, other scholars predict a prolonged existence of more liquid-rich (potentially eruptible) mush bodies within the crust. In this case, the lack of currently observed geophysical signals for large, melt-rich magma bodies may simply result from the ephemeral nature of magmatism. To make progress, more information about the longevity of eruptible mushy regions is essential. This proposal will develop a new method to determine the lifetime of melt-rich regions, enabling us to resolve this current conflict. Time 'chronology' information about volcanic systems is commonly recorded in the mineral zircon, which contains radioactive elements that are sensitive to time. Zircon chronology shows that crystal mushes can persist over long time periods (e.g. 100s kyr), but these measurements hold significant uncertainties. The lifetime of the more eruptible, melt-rich 'mobile magma' is much harder to investigate, because it occurs at higher temperatures where zircon may not be stable. However, this information is a critical link between geophysical observations, which record a snapshot of the state of the earth's crust, and volcanology, which records information about magmatic processes over very long times. This project will develop a new method to determine the lifetime of mobile magma crystallisation directly by analysing crystals that grow from melt at high temperatures. Specifically, we will relate the aspect ratio (length/ width) of the silicate mineral plagioclase, which grows from almost all subduction zone magmas, to the time available for crystallisation. Our preliminary work suggests a strong relationship between aspect ratio and time for water-rich, silica-rich magmas that erupt at subduction zones. Using high-temperature experiments, analysis of well-dated plagioclase crystals, and mathematical approaches, the team will derive a universal relationship that can be applied to all magmatic environments. We will apply the method to intermediate subduction zone volcanic systems that have recent geophysical information, in order to re-evaluate the architecture of the subterranean magma plumbing systems. Finally, we will integrate our crystal-scale observations with existing geophysical information and chronology datasets, to bring new insights into the distribution of melt and our ability to see it geophysically. This will lead to novel constraints on the identification, recognition and definition of mushy plumbing systems in future.

火山主义 - 从地球内部内部熔融岩石的产生和喷发 - 是板块构造最明显的表现之一。当岩浆被储存和固化在地壳中，或者在地球表面爆发时，地壳的生长要么发生。俯冲带的爆发活动可能具有爆炸性和高度破坏性，代表着重要的自然危害，对生命，健康和财务稳定的影响产生影响。火山学家面临的主要挑战之一是对这种喷发行为的准确预测。过去火山活动的大量证据表明，在一次事件中可以爆发大量岩浆。但是，用于图像地球表面图像的地球物理技术无法区分地壳中存储的大量熔体（岩浆液体）。取而代之的是，熔体可以存储为“水晶糊”，即火山晶体的积累仅被少量熔体隔开，而熔体很难在地球物理上进行图像。但是，熔融含量低的晶体糊性像固体，无法爆发。因此，研究人员认为，糊状物包含具有较高熔体含量的“爆发”透镜，但仍然足够薄，无法通过地球物理技术解决。如果是这样，那么整个糊状区域中晶体和液体的批发空间重组可能会改变其整体物理行为，从而迅速变得爆发。相比之下，其他学者预测，地壳内的液体糊状物体较长（潜在的爆发）糊状体长期存在。在这种情况下，目前缺乏针对大型，富含融化的岩浆体的地球物理信号可能仅仅是由于岩浆的短暂性而产生的。为了取得进展，有关糊状糊状区域寿命的更多信息至关重要。该建议将开发一种新方法来确定熔融丰富的地区的寿命，从而使我们能够解决当前的冲突。有关火山系统的时间“年代”信息通常记录在矿物锆石中，其中包含对时间敏感的放射性元素。锆石的时间顺序表明，晶体糊可能会在长时间内持续存在（例如100s kyr），但是这些测量值具有明显的不确定性。更爆发，融化的“移动岩浆”的寿命更难研究，因为它发生在锆石可能不稳定的较高温度下。但是，这些信息是地球物理观察结果之间的关键联系，它记录了地球状态状态的快照和火山学，它在很长一段时间内记录了有关岩浆过程的信息。该项目将开发一种新方法，通过分析在高温下从熔体生长的晶体直接确定移动岩浆结晶的寿命。具体而言，我们将将硅酸盐矿物斜长石的纵横比（长度/宽度）与从几乎所有俯冲区岩浆生长，与可用于结晶的时间相关联。我们的初步工作表明，在俯冲区域爆发的水丰富，富含二氧化硅的岩浆的时间与时间之间存在牢固的关系。使用高温实验，分析良好的斜长石晶体以及数学方法，团队将得出可以应用于所有岩浆环境的普遍关系。我们将将该方法应用于具有近期地球物理信息的中间俯冲带火山系统，以重新评估地下岩浆管道系统的结构。最后，我们将将我们的晶体尺度观察结果与现有的地球物理信息和年表数据集相结合，以使融化分布的新见解以及我们从地球物理看待它的能力。这将导致对未来糊状管道系统的识别，识别和定义的新限制。