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A sub-volcanic chemical pump: experimental and theoretical investigations of volatile element transport beneath volcanoes

火山下化学泵：火山下挥发性元素传输的实验和理论研究

基本信息

批准号：
NE/F017421/1
负责人：
Jonathan Blundy
金额：
$ 39.15万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF017421%2F1
关键词：
sub volcanic chemical pump experimental

项目摘要

Explosive volcanic eruptions are driven by the release of volcanic gases stored in underground magma bodies. These gases can carry an abundance of trace elements, some of which are released into the atmosphere, some are redistributed through the sub-volcanic magma body and others are concentrated and precipitated as hydrothermal ore deposits. Understanding how volcanic gases transport trace elements and where they go is therefore of central importance in our understanding of both volcano dynamics and hydrothermal ore formation. This proposal builds on considerable previous work on Mount St. Helens volcano in the USA. This work has documented a number of lines of evidence that certain volatile trace elements, such as Li and Pb, are efficiently moved from one part of the magma body to another. Why they are released from some parts of the magma body and accumulate in others is not well understood. The reason for this is that the ability of trace elements to dissolve in volcanic gases is not well constrained. A key unknown is the partitioning of trace elements between coexisting silicate melts and volcanic gas as a function of pressure, temperature and gas composition. A compounding problem is that some gases are homogeneous when released from magma at depth but condense to two separate phases at shallower pressure. Again, how trace elements partition between these separate phases is not well constrained, although it has been proposed that this type of vapour condensation is key to the formation of hydrothermal ore bodies. Based on our studies at Mount St. Helens we have hypothesised that the pressure drop in a magma body following major eruptions may lead first to condensation of vapour and then the redissolving of this vapour as the magma becomes repressurised at the end of the eruption. This constitutes a novel sort of 'chemical pump', which we want to test out by means of this proposal. To do this we plan to use high pressure and temperature experiments to determine the partitioning of selected trace elements between coexisting melt and vapour and to combine this with further studies of trace elements trapped in tiny globules of glass, known as melt inclusions, in volcanic crystals. The virtue of studying melt inclusions is that they effectively trap the pre-eruptive volatile inventory, including trace element, prior to eruption and therefore hold clues to the conditions under which magma was stored and how gases move around within this magma. Our experimental studies will be allied to dynamical models of volcanic processes using a new 2D computer code developed by the Visiting Researcher. This code has had considerable success in explaining many enigmatic features of volcano behaviour but has never before been applied to the problems of gas escape, gas redistribution and gas retention that occur during and after an eruption. We propose that the concentration of volatile trace elements in melt inclusions is a valuable archive of sub-volcanic degassing processes. Unlocking this archive requires the kind of integrated geochemical, petrological and theoretical study proposed here.

火山爆发是由地下岩浆体中储存的火山气体的释放推动的。这些气体可以携带丰富的微量元素，其中一些释放到大气中，一些通过次火山岩浆体重新分配，另一些作为热液矿床浓缩和沉淀。因此，了解火山气体如何输送微量元素及其去向，对于我们理解火山动力学和热液成矿作用具有重要意义。这项建议建立在美国圣海伦斯火山之前的大量工作基础上。这项工作记录了一系列证据，证明某些挥发性微量元素，如锂和铅，可以有效地从岩浆体的一个部分转移到另一个部分。为什么它们从岩浆体的某些部分释放出来，并积聚在其他部分，目前还不太清楚。原因是微量元素在火山气体中的溶解能力没有得到很好的限制。一个关键的未知因素是微量元素在共存的硅酸盐熔体和火山气体之间的分配，这是压力、温度和气体组成的函数。一个复杂的问题是，一些气体在深部从岩浆中释放时是均匀的，但在较浅的压力下凝结成两个独立的相。同样，微量元素如何在这些不同的相之间分配没有得到很好的限制，尽管有人提出这种类型的蒸汽冷凝是形成热液矿体的关键。根据我们在圣海伦斯山的研究，我们推测，大喷发后岩浆体中的压力下降可能首先导致水蒸气的凝结，然后随着岩浆在喷发结束时重新加压，水蒸气重新溶解。这构成了一种新的‘化学泵’，我们想通过这个方案来测试它。为了做到这一点，我们计划利用高压和温度实验来确定选定的微量元素在共存的熔体和蒸气之间的分配，并将其与进一步研究火山晶体中被称为熔体包裹体的微小玻璃球体中的微量元素结合起来。研究熔体包裹体的优点是，它们有效地捕获了喷发前的挥发性库存，包括喷发前的微量元素，因此掌握了岩浆储存条件和气体在岩浆中如何移动的线索。我们的实验研究将与火山过程的动力学模型相结合，使用由访问研究员开发的新的2D计算机代码。这一准则在解释火山行为的许多神秘特征方面取得了相当大的成功，但以前从未被应用于喷发期间和喷发后发生的气体逃逸、气体再分配和气体滞留问题。我们认为，熔体包裹体中挥发性微量元素的浓度是次火山脱气过程的有价值的档案。解锁这一档案需要这里提出的那种综合的地球化学、岩石学和理论研究。

项目成果

期刊论文数量（10）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Subvolcanic plumbing systems imaged through crystal size distributions

通过晶体尺寸分布成像的次火山管道系统

DOI：
10.1130/g31691.1
发表时间：
2011
期刊：
Geology
影响因子：
5.8
作者：
Melnik O
通讯作者：
Melnik O

Formation of magmatic brine lenses via focussed fluid-flow beneath volcanoes

DOI：
10.1016/j.epsl.2018.01.013
发表时间：
2018-03-15
期刊：
EARTH AND PLANETARY SCIENCE LETTERS
影响因子：
5.3
作者：
Afanasyev, Andrey;Blundy, Jon;Sparks, Steve
通讯作者：
Sparks, Steve

Gas-driven filter pressing in magmas: Insights into in-situ melt segregation from crystal mushes

DOI：
10.1130/g36766.1
发表时间：
2015-08
期刊：
Geology
影响因子：
5.8
作者：
M. Pistone;F. Arzilli;K. Dobson;Benoît Cordonnier;E. Reusser;P. Ulmer;F. Marone;A. Whittington;Lucia;Mancini;J. L. Fife;Jonathan D. Blundy
通讯作者：
M. Pistone;F. Arzilli;K. Dobson;Benoît Cordonnier;E. Reusser;P. Ulmer;F. Marone;A. Whittington;Lucia;Mancini;J. L. Fife;Jonathan D. Blundy

Generation of porphyry copper deposits by gas-brine reaction in volcanic arcs