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Scales and frequencies of Snake-River type super-eruptions of the Yellowstone hot-spot track, USA

美国黄石热点轨迹蛇河型超级喷发的规模和频率

基本信息

批准号：
NE/G005672/1
负责人：
Michael Branney
金额：
$ 61.44万
依托单位：
University of Leicester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG005672%2F1
关键词：
Scales frequencies Snake River type

项目摘要

This project concerns the largest explosive eruptions on Earth. Super-eruptions are amongst the most catastrophic events that affect the Earth's surface: they have immediate and devastating regional environmental consequences and affect global climate. To assess their role with regard to crustal evolution, regional or global environmental change, we first need to need to know more about how often they occur, at what scales, and about the eruption styles. To do this we must consult the geologic record. But despite recent interest, relatively few examples are known and still fewer have been studied in detail. Most work has been on reconstructing single examples in far-flung locations (e.g. Toba volcano in Indonesia). We plan a different and complementary approach: to quantify the number, frequencies and volumes of successive large eruptions over an extended period at a single geotectonic setting. We know something about the frequencies of large eruptions during relatively short periods of time at continental arcs (e.g. Taupo Volcanic Zone; San Juan Mts) but there is virtually no quantitative work on super-eruption frequencies in the continental intraplate setting - despite a growing realisation of the importance of silicic volcanism within Large Igneous Provinces. It is well-known that Yellowstone, USA, has erupted catastrophically in recent times, but perhaps less widely appreciated is that this was just the last of a series of numerous very large explosive eruptions that burned a track along the Snake River eastwards from Oregon to Yellowstone from 16 Ma to present. Some of the earlier eruptions were probably as large as at Yellowstone, if not larger, but we know astonishingly little about them: we do not even know how many occurred, or their true extents. This is despite the region being one of the Earth's largest, most accessible, and best-preserved silicic volcanic provinces; yet large tracts of it remain unstudied and the overall stratigraphy has not been resolved. Magma erupted in a super-eruption is pulverised and enters vast ground-hugging density currents that deposit thick layers of ash, called 'ignimbrites'. Repetition of similar eruptions in the Snake River Plain has produced many broadly similar ignimbrites that are not simple to tell apart from one another. Therefore, we shall divide local successions into 'eruption-units' and then fingerprint each unit in detail using a combination of detailed physical and chemical analysis, dating, and palaeomagnetic tools; for example, recording any distinctive vertical variations in the chemistry of the crystals and glasses. Preliminary fieldwork, mineral chemistry and 40Ar-39Ar has already allowed us to correlate two units in adjacent ranges and gives us confidence to predict that the detailed approach planned will, for the first time, let us to correlate individual units across large distances, and so establish the number and volumes of the eruptions. The age data together with the palaeomagnetic data for each unit will provide a new regional time-event framework, to interpret the province's eruption history and assess whether the volumes and frequencies of large explosive eruptions have changed through time, including comparison with the known data from the Yellowstone area. The site of volcanism shifted eastwards with time, enabling us to consider spatial variations and possible links with crustal deformation. The work will add to future understanding about what controls eruptions on this large scale (e.g. heat flux at depth?), about rates of magma generation and storage, and the inter-relationships between magmatism and the crust. The multidisciplinary research team has much experience in the methods to be employed, and in the Columbia River - Yellowstone Volcanic Province. Developing, for the first time, a long-needed regional time-event framework, and drawing together the different research groups will act as a catalyst for extensive further research.

该项目涉及地球上最大的爆炸性喷发。超级火山爆发是影响地球表面的最具灾难性的事件之一：它们对区域环境造成直接和毁灭性的后果，并影响全球气候。为了评估它们在地壳演化、区域或全球环境变化方面的作用，我们首先需要更多地了解它们发生的频率、规模和喷发类型。要做到这一点，我们必须查阅地质记录。但是，尽管最近的兴趣，相对较少的例子是已知的，更少的是已经详细研究。大多数工作是在遥远的地方重建单个例子（例如印度尼西亚的多巴火山）。我们计划一个不同的和互补的方法：量化的数量，频率和连续的大喷发量在一个单一的大地构造设置在一个较长的时间。我们对大陆弧（例如陶波火山带;圣胡安山脉）在相对较短的时间内大喷发的频率有所了解，但实际上没有关于大陆板内环境中超级喷发频率的定量研究-尽管人们越来越认识到大火成岩省内火山活动的重要性。众所周知，美国黄石公园最近发生了灾难性的喷发，但也许没有得到广泛认识的是，这只是16 Ma至今一系列巨大爆发中的最后一次，这些爆发沿着沿着蛇河向东从俄勒冈州到黄石公园。早期的一些火山爆发可能和黄石公园一样大，如果不是更大的话，但我们对它们的了解少得可怜：我们甚至不知道发生了多少次，也不知道它们的真实范围。这是尽管该地区是地球上最大的，最容易进入，保存最好的火山省份之一，但它的大部分仍然没有研究，整体地层尚未解决。在超级火山爆发中喷发的岩浆被粉碎，进入巨大的地面拥抱密度流，存款厚厚的灰烬层，称为“熔结凝灰岩”。斯内克河平原重复的类似喷发产生了许多大致相似的熔结凝灰岩，它们之间并不容易区分。因此，我们将把局部层序划分为“喷发单元”，然后结合详细的物理和化学分析、测年和古地磁工具，对每个单元进行详细的指纹分析;例如，记录晶体和玻璃化学成分的任何独特的垂直变化。初步的野外工作，矿物化学和40 Ar-39 Ar已经使我们能够将相邻范围内的两个单元相关联，并使我们有信心预测，计划的详细方法将首次让我们将远距离的单个单元相关联，从而确定喷发的数量和体积。每个单元的年龄数据和古地磁数据将提供一个新的区域时间-事件框架，以解释该省的火山喷发历史，并评估大规模爆发的数量和频率是否随时间而变化，包括与黄石地区的已知数据进行比较。火山活动的地点随着时间向东移动，使我们能够考虑空间变化和与地壳变形的可能联系。这项工作将增加未来对是什么控制着这种大规模喷发的理解（例如，深度的热通量？），关于岩浆生成和储存的速率，以及岩浆活动和地壳之间的相互关系。多学科研究小组在所采用的方法方面有很多经验，并在哥伦比亚河-黄石火山省。第一次制定一个长期需要的区域时间-事件框架，并将不同的研究小组聚集在一起，将促进进一步的广泛研究。