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.

火山爆发是由储存在地下岩浆体中的火山气体的释放驱动的。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布，另一些则作为热液矿床浓缩和沉淀。因此，了解火山气体如何运输微量元素及其去向对于我们了解火山动力学和热液矿石形成至关重要。该提案建立在美国圣海伦斯火山先前大量工作的基础上。这项工作记录了一系列证据，表明某些挥发性微量元素（例如锂和铅）可以有效地从岩浆体的一个部分转移到另一部分。为什么它们从岩浆体的某些部分释放并在其他部分积聚尚不清楚。其原因是微量元素溶解在火山气体中的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，作为压力、温度和气体成分的函数。一个复杂的问题是，一些气体从深部岩浆中释放出来时是均质的，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单独的相之间分配并没有得到很好的限制，尽管有人提出这种类型的蒸气冷凝是热液矿体形成的关键。根据我们在圣海伦斯火山的研究，我们假设，大规模喷发后岩浆体内的压力下降可能首先导致蒸气凝结，然后随着岩浆在喷发结束时重新加压，蒸气会重新溶解。这构成了一种新型的“化学泵”，我们希望通过该提案对其进行测试。为此，我们计划使用高压和高温实验来确定所选微量元素在共存熔体和蒸气之间的分配，并将其与火山晶体中微小玻璃球（称为熔体包裹体）中捕获的微量元素的进一步研究结合起来。研究熔体包裹体的优点在于，它们可以在喷发前有效地捕获喷发前的挥发性物质，包括微量元素，因此可以提供有关岩浆储存条件以及气体如何在岩浆内移动的线索。我们的实验研究将使用访问研究员开发的新的二维计算机代码与火山过程的动力学模型结合起来。该规范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，但以前从未应用于喷发期间和喷发后发生的气体逃逸、气体重新分布和气体滞留问题。我们认为熔体包裹体中挥发性微量元素的浓度是火山下脱气过程的宝贵档案。解锁这个档案需要这里提出的综合地球化学、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