New advances in Ar-Ar geochronology and novel applications to global tectonics

测定岩石年代最有用的方法之一是基于钾（40K）到氩（40Ar）的放射性衰变，它在巨大的地质和天文时间跨度中充当了一个长寿的时钟。氩-40 /氩-39 （Ar-Ar）测年技术是K-Ar地质年代法的一种变体，是了解世界各地地质演化的最有用的测年工具之一。然而，要理解我们所获得的Ar-Ar年龄的意义，就需要详细了解气态Ar原子是如何在岩石和晶体中扩散的。许多因素，如晶体结构、矿物化学、溶解度和晶体结构中缺陷的存在控制着扩散行为，它们的影响将通过实验室实验和数值模拟在最常见的岩石形成和年代久远的矿物类型之一云母中进行研究。使用各种分析技术对不同类型的云母进行实验，可能会导致矿物中Ar扩散的新范式，从而更准确地解释我们测量的年龄。最近的研究表明，我们对40K到40Ar衰减率的准确性和精度的认识有待提高；在第二个相关主题中，提出了独特的实验，将从第一性原理测量人工富集40K源产生的原位40Ar衰变速率。这将使Ar-Ar年龄与其他地质年代学系统的年龄进行更准确的比较。人们普遍认为，超级大陆的形成对地壳、大气、气候和生命的演变有着深远的影响。该研究的最后一个主题将应用上述知识，对导致最新超级大陆盘古大陆形成的机制施加亟需的年龄限制，提供一个可以评估更古老超级大陆起源的模板，并解决我们对指导地球最近地质演化的主要全球构造力的认识上的根本空白。该研究项目将在资助期内培养至少3名博士生、4名硕士生和5名研究助理。

One of the most useful methods of dating rocks is based on the radioactive decay of potassium (40K) to argon (40Ar), which serves as a long-lived clock over the vast span of geologic and astronomic time. The argon-40 / argon-39 (Ar-Ar) dating technique - a variant of the K-Ar geochronological method - is one of the most useful dating tools in understanding the geological evolution of regions around the world. Understanding the significance of the Ar-Ar ages we obtain, however, requires a detailed understanding of how the gaseous Ar atoms diffuse through the rocks and crystals in which they accumulate. Many factors such as crystal structure, mineral chemistry, solubility, and the presence of defects in the crystal structure control diffusional behaviour, and their effects will be studied through laboratory experiments and numerical modelling in one of the most common rock-forming and dated mineral types - the micas. Experiments using various analytical techniques on different types of mica may lead to a new paradigm for Ar diffusion in minerals and thus, a more accurate interpretation of the ages that we measure. Recent studies have shown that our knowledge of the accuracy and precision of the decay rate of 40K to 40Ar needs to be improved; in a second related theme, unique experiments are proposed which will measure from first principles the in-situ 40Ar decay rate produced from an artificially enriched 40K source. This will enable more accurate comparisons of Ar-Ar ages with ages from other geochronological systems. The formation of supercontinents is widely accepted to have a profound effect on the evolution of the Earth's crust, atmosphere, climate, and life. A final theme of the proposed research will apply the above knowledge to place much-needed age constraints on the mechanisms that led to the formation of the latest supercontinent, Pangea, provide a template by which the origin of older supercontinents can be evaluated, and address a fundamental gap in our knowledge of the major global tectonic forces that have guided the Earth's recent geological evolution. This research program will train at least 3 PhD students, 4 MSc students and 5 research assistants over the duration of the proposed funding.