Understanding excess argon by ultra-high resolution 40Ar/39Ar laserprobe analysis

通过超高分辨率 40Ar/39Ar 激光探针分析了解过量氩气

• 批准号: NE/F020066/1
• 负责人: Sarah Sherlock
• 金额: $ 62.71万
• 依托单位: The Open University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 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%2FF020066%2F1
• 关键词: Understanding; excess; argon; ultra; resolution

This project uses an impressive new methodology that we have developed, to investigate and quantify how extra amounts of argon enter minerals and rocks when they are within the Earth's crust. This is particularly important to understand because this extra argon causes havoc for geochronologists (researchers that are focussed on finding out the timescales and rates of geological processes) because it artificially increases the ages of the rocks and minerals, and so many seem to be older than they really are. The technique that the geochronologists use that is susceptible to this problem is 40Ar/39Ar dating, which is one of the most versatile radiometric dating techniques available, and also the most widely applied. Absolute, or radiometric, ages are based on the radioactive decay of one isotope to another within individual minerals; the reason why 40Ar/39Ar is perhaps one of the most versatile is because it is based on the decay of potassium to argon, and potassium is one of the most abundant elements in rocks and minerals on Earth. It is important that we understand why 40Ar/39Ar ages are often inaccurate because the ages strongly influence our interpretation of Earth processes, and wider still the Earth-Moon system. For two centuries or thereabouts, geologists have placed rocks and processes in chronological order, but it is the geochronologists, or age-daters, that in the last few decades have pinned absolute ages on these relative timescales of such events as large volcanic eruptions, meteorite impacts, even times of fluid flow in oil reservoirs. The 40Ar/39Ar dating technique is nearly 40 years old, but we are finding that with each new technological development we are able to learn more about the way argon behaves in different minerals during Earth processes. In some cases our newfound knowledge has shed light on why many ages did not fit with the chronology which was based on palaeomagnetims or rates of sediment deposition, and with technological advances we have been able to improve these ages. However, we and many others still find that 40Ar/39Ar ages are often older than they should be, because of this 'nuisance' additional component of argon, that we term 'excess argon'. We know a little about it: that in some metamorphic rocks it tends to pervade those that have more potassium, it is often abundant where rocks are deformed in the Earth's crust and the planes of weakness have been exploited by fluids, and we know that the composition and temperature of these fluids can affect how much of this 'excess argon' enters the rock or mineral. What we really don't understand though is where excess argon comes from, how far it travels, and how it gets into minerals in the simplest rocks. This is what we are proposing to investigate through an integrated study of 40Ar/39Ar ages, in comparison with another isotopic dating technique, and a series of analytical techniques for establishing the composition of the rocks, minerals and fluids in simple rocks. This has not been done before because the technology has not kept pace with theoretical development. We have been working since 2005 to develop the necessary technology, and we believe that we have achieved this, which we have demonstrated on page 6 with pilot data. By undertaking one of the most detailed studies ever proposed, we aim to transform this nuisance into a tool to measure the distances travelled by fluids within and between rocks and minerals in the Earths crust, and ultimately improve our understanding of rates and timescales of geological processes.

该项目使用我们开发的令人印象深刻的新方法，调查和量化额外数量的氩气在地球壳内时如何进入矿物质和岩石。理解这一点尤其重要，因为这种额外的氩气会给地球体学家（重点是找出地质过程的时间尺度和速率）造成严重破坏），因为它人为地增加了岩石和矿物质的年龄，而且似乎比实际年龄更大。地球体学家使用的技术易受此问题的技术是40AR/39AR日期，这是使用最广泛的辐射测年技术之一，也是最广泛的应用。绝对或辐射测定年龄是基于一个同位素的放射性衰减，而单个矿物质中另一种同位素的放射性衰减； 40AR/39AR可能是最通用的原因之一是因为它基于钾对氩气的腐烂，而钾是地球上岩石和矿物质中最丰富的元素之一。重要的是要了解为什么40AR/39AR年龄通常是不准确的，因为年龄强烈影响我们对地球过程的解释，并且更广泛的地球系统。在两个世纪左右的时间里，地质学家一直按时间顺序排列岩石和过程，但是地球文学家或年龄段的人在过去的几十年中，已经将绝对年龄限制在这些相对时间表上，例如大型火山爆发，即使在油库中流动的流动时间，甚至是流体流动的时间。 40AR/39AR约会技术已有近40年的历史，但是我们发现，随着每种新技术的发展，我们都能进一步了解氩气在地球过程中不同矿物质的方式。在某些情况下，我们的新知识已经阐明了为什么许多年龄不符合基于古征或沉积物的速率的年表，并且随着技术进步，我们能够改善这些年龄。但是，我们和许多其他人仍然发现40AR/39AR年龄通常比应有的年龄要大，因为这种“令人讨厌的”其他组成部分，我们称我们为“多余的氩气”。我们对此有所了解：在某些变质岩石中，它往往会遍及那些钾的人，通常在地壳中岩石变形，而弱点的岩石的变形通常是丰富的，而弱点的平面已经被油漏了，我们知道这些流体的组成和温度会影响这些多余的岩石或岩石的岩石。不过，我们真正不明白的是多余的氩气来自何处，旅行多远以及如何进入最简单的岩石中。与另一种同位素约会技术相比，我们提议通过对40AR/39AR年龄的综合研究进行研究，以及一系列用于在简单岩石中建立岩石，矿物质和流体组成的分析技术。以前没有这样做，因为该技术尚未与理论发展保持同步。自2005年以来，我们一直在工作以开发必要的技术，我们相信我们已经实现了这一目标，我们在第6页上使用了Pilot Data证明了这一点。通过进行有史以来最详细的研究之一，我们旨在将这种滋扰转变为一种工具，以测量地壳中岩石和矿物质之间以及矿物质之间的流体传播的距离，并最终提高我们对地质过程的速度和时间表的理解。

项目成果

Understanding Extraneous Argon in Silicic Volcanic Products Using

使用了解硅质火山产品中的外来氩

• DOI: 10.21954/ou.ro.0000f061
• 发表时间: 2013
• 作者: Wilkinson C

Observation of centimetre-scale argon diffusion in alkali feldspars: implications for 40 Ar/ 39 Ar thermochronology

碱长石中厘米级氩扩散的观察：对 40 Ar/ 39 Ar 热年代学的影响

• DOI: 10.1144/sp378.25
• 发表时间: 2013
• 期刊: Geological Society, London, Special Publications
• 作者: Flude S

Partitioning of excess argon between alkali feldspars and glass in a young volcanic system

• DOI: 10.1016/j.chemgeo.2011.07.005
• 发表时间: 2011-10
• 期刊: Chemical Geology
• 影响因子: 3.9
• 作者: P. Clay;S. Kelley;S. Sherlock;T. Barry