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Crystal forensics: constraining the timescales of magmatic processes leading to volcanic eruptions

晶体取证：限制导致火山喷发的岩浆过程的时间尺度

基本信息

批准号：
NE/G01292X/1
负责人：
Katharine Saunders
金额：
$ 37.57万
依托单位：
University of Bristol
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG01292X%2F1
关键词：
Crystal forensics constraining timescales magmatic

项目摘要

Volcanoes erupt daily and are an everyday hazard for millions of people worldwide. Today, active volcanoes are continuous monitored looking for signs of imminent eruptions. However, in order for the accurate prediction of future eruptions to be achieved a comprehensive knowledge of the internal workings of volcanoes is required, including the timescales over which molten rock moves through the volcano. Magma is molten rock composed of liquid rock and solid particles called crystals. The migration of magma through the Earth's crust and the eventual eruption is complex, however a record of this is preserved in crystals. Just as your favourite crime drama uses forensic science to solve the crime, we can do the same with the composition of minerals from volcanic eruptions. The life of a crystal is not simple but a complex one involving periods of growth and melting, migration and periods of residence in different magma bodies until eventually the crystal is erupted and the composition frozen in. Each of these experiences are preserved in the crystal as chemical or textural markers, that results in highly zoned crystals. These crystal zones can be treated in just the same way as tree rings which record the growth history of a tree. The chemical composition of individual zones can be used to fingerprint the magmatic process that formed the zone and we can use the difference in the chemical composition between two adjacent zones to determine the timescale over which these magmatic processes occurred. Immediately after formation the compositional difference between two adjacent zones is sharp, but with time diffusion of elements (migration of small particles that the crystal is made from) smoothes this compositional boundary and this can be used to calculate the timescale of magmatic processes. Importantly, different elements migrate through the crystal structure at differ rates and therefore a whole range of magmatic processes that occur on the timescales of hours to months prior to eruption can be investigated. However, the zoning in these crystals occur on a sub-micron scale (smaller than the width of a human hair). Therefore, for the first time this study will use the new generation of high resolution Secondary Ion Mass Spectrometers permitting the measurement of fine-scale chemical zonation of plagioclase crystals from Mount St. Helen's in the USA and Mount Taranaki in New Zealand. This will allow the magmatic processes and the timescales over which these processes occurred directly prior to eruption to be assessed. These timescales can then be evaluated against the known timescales for the movement of magma prior to the recent eruptions of Mount St. Helen's allowing better models for the future prediction of volcanic eruptions to be constrained. This will provide valuable insights into the working of volcanos directly prior to eruption and could have immense benefits to the millions of people worldwide who live in the shadow of volcanoes and help mitigate the associated hazards of active volcanoes. This research will be conducted in the Department of Earth Sciences, University of Bristol in conjunction with the Interface Analysis Centre, Bristol, Muenster University, Germany, University of Western Australia, Cascades Volcano Observatory and University of Orogen in the USA and Victoria University of Wellington, New Zealand.

火山每天都在喷发，对全世界数百万人来说是一种日常威胁。今天，人们对活火山进行持续监测，寻找即将爆发的迹象。然而，为了准确预测未来的喷发，需要对火山内部活动有全面的了解，包括熔岩在火山中移动的时间尺度。岩浆是由液态岩石和被称为晶体的固体颗粒组成的熔融岩石。岩浆穿过地壳的迁移和最终的喷发是复杂的，然而这一过程的记录保存在晶体中。就像你最喜欢的犯罪剧用法医科学来破案一样，我们也可以用同样的方法来研究火山喷发的矿物成分。晶体的生命不是简单的，而是复杂的，包括生长和融化、迁移和在不同岩浆体中居住的时期，直到最终晶体喷发，其成分被冻结。每一种经历都作为化学或纹理标记保存在晶体中，从而形成高度分带的晶体。这些晶体区域可以像记录树木生长历史的年轮一样被处理。单个带的化学成分可以用来确定形成带的岩浆过程的指纹，我们可以利用两个相邻带之间化学成分的差异来确定这些岩浆过程发生的时间尺度。在形成后，两个相邻区域之间的成分差异是明显的，但随着时间的推移，元素的扩散（构成晶体的小颗粒的迁移）使这一成分边界变得平滑，这可以用来计算岩浆过程的时间尺度。重要的是，不同的元素以不同的速率在晶体结构中迁移，因此可以研究喷发前几个小时到几个月时间尺度上发生的一系列岩浆过程。然而，这些晶体中的分带发生在亚微米尺度上（比人类头发的宽度还小）。因此，本研究将首次使用新一代高分辨率二次离子质谱仪，可以测量来自美国圣海伦山和新西兰塔拉纳基山的斜长石晶体的精细化学带。这将使岩浆过程和这些过程直接发生在喷发之前的时间尺度得以评估。然后，这些时间尺度可以与圣海伦火山最近爆发之前的岩浆运动的已知时间尺度进行评估，从而为未来火山爆发的预测提供更好的模型。这将为火山喷发前的直接工作提供有价值的见解，并可能为全世界数百万生活在火山阴影下的人们带来巨大的利益，并有助于减轻活火山的相关危害。这项研究将在布里斯托尔大学地球科学系与布里斯托尔界面分析中心、德国明斯特大学、西澳大利亚大学、美国喀斯喀特火山观测站和造山大学以及新西兰惠灵顿维多利亚大学联合进行。