In Situ Mineral Analysis of Earth's Early Crust and Impact Rocks by LA-(MC)-ICPMS

人们对地球历史的前半段知之甚少，但就第一批大陆的形成、富氧大气和生命的初步发展以及大量小行星和彗星对地球表面的轰击而言，这是一个关键时期。在所有这些领域取得进展的关键是建立一个全面的、自我一致的模型，该模型说明大陆是如何以及何时从地幔中剥离出来的，地球表面的条件是如何变得适合生命生存的，这与年轻的太阳系中大量岩石和冰体撞击的原因和影响有关。我的研究创造了关于大陆形成的关键领域的知识，以及构建这样一个全面模型所需的陨石坑过程的作用。我使用的方法将自动扫描电子显微镜成像的新发展与激光烧蚀ICP质谱的原位分析相结合，以识别特定的矿物颗粒或颗粒域，这些矿物颗粒或颗粒域保存了地壳变质或冲击期间岩浆结晶或再结晶的记录。未来五年将实施三个项目。一种方法是利用古代岩石中矿物的放射性同位素组成来确定40亿到25亿年前形成大陆的地幔元素的枯竭程度。它还可能确定地球上保存着年龄超过40亿年的岩石和矿物的地方，这是极其罕见的。第二项研究考察了撞击冲击变质作用对拉布拉多北部一个小的、最近的、但大部分未被勘探的陨石坑形成的矿物的放射性成因同位素组成的影响，以记录同位素标准，这些标准可用于识别古代地质记录中受小陨石坑事件影响的矿物。第三种方法是测量月球陨石中矿物质的放射性同位素组成，以确定它们如何受到非常大的撞击事件的影响。我的研究项目的副产品是用于寻找矿物和碳氢化合物资源的原位矿物分析的分析方法，以及其他学科，如环境中的污染物追踪和监测气候变化。

The first half of Earth's history is very poorly understood but was a critical time in terms of creation of the first continents, initial development of an oxygen-rich atmosphere and life, and bombardment of large numbers of asteroids and comets on its surface. The key to progress in all of these areas is a comprehensive, self-consistent model of how and when the continents were extracted from the mantle and conditions at Earth's surface became suitable for life, linked to the causes and effects of large numbers of impacts with rocky and icy bodies in the young solar system. My research creates knowledge on critical areas of continent formation and the role of impact cratering processes that is needed to construct such a comprehensive model. The approach I use couples new developments in automated scanning electron microscopic imaging with in situ analysis by laser ablation ICP mass spectrometry to identify specific mineral grains or grain domains that preserve a record of crystallization from a magma or recrystallization during crustal metamorphism or impact shock. Three projects will be carried out over the next five years. One uses the radiogenic isotope compositions of minerals in ancient rocks to determine the extent to which Earth's mantle was depleted in elements that formed the continents between about 4.0 and 2.5 billion years ago. It may also identify places on Earth that preserve rocks and minerals older than 4 billion years in age, which are exceedingly rare. The second examines the effect of impact shock metamorphism on the radiogenic isotope compositions of minerals formed in a small, recent, but largely unexplored crater in northern Labrador, to document isotopic criteria that may be used to identify minerals in the ancient geological record that were affected by impact in small cratering events. The third measures the radiogenic isotope compositions of minerals in lunar meteorites to determine how they were affected by very large impact events. Spin-offs of my research program are analytical methods for in situ mineral analysis that are being applied to the search for mineral and hydrocarbon resources, and other disciplines such as contaminant tracing in the environment and monitoring climate change.