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

点击翻译按钮获取中文摘要

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.