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

Ar-Ar地质年代学的新进展及其在全球构造学中的新应用

• 批准号: 184211-2011
• 负责人: Lee, James
• 金额: $ 2.04万
• 依托单位: Queen's University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=546010
• 关键词: New; advances; Ar; geochronology; novel

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.

最有用的岩石测年方法之一是基于钾(40K)到氩(40Ar)的放射性衰变，这是一个跨越地质和天文时间跨度的长寿钟。Ar-40/Ar-39(Ar-Ar)测年技术--K-Ar年代学方法的一种变体--是理解世界各地地质演化的最有用的测年工具之一。然而，要想了解我们获得的Ar-Ar年龄的意义，需要详细了解气态Ar原子是如何在它们聚集的岩石和晶体中扩散的。晶体结构、矿物化学、溶解度和晶体结构中缺陷的存在等许多因素控制着扩散行为，它们的影响将通过实验室实验和数值模拟在最常见的成岩和过时矿物类型之一-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，可能会导致一种新的Ar在矿物中扩散的范例，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确度的了解需要改进；在第二个相关主题中，提出了独特的实验，将从第一原理测量人工浓缩40K源产生的现场40Ar衰减率。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、气候和生命的演化产生了深远的影响。拟议研究的最后一个主题将应用上述知识，对导致最新的超级大陆--盘古大陆形成的机制施加亟需的年龄限制，提供一个模板，用来评估较老的超级大陆的起源，并解决我们对指导地球最近地质演化的主要全球构造力量的基本认识空白。这项研究计划将在拟议的资金期限内培训至少3名博士生、4名硕士学生和5名研究助理。