Constraining the Secular Compositional Evolution of the Upper Continental Crust Using Ancient Glacial Deposits and Creation of an Upper Crustal Reference Suite

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The Earth is unique amongst the planets of our Solar System in having a crust of silica-rich, low-density rock that forms our continents. It is upon this platform that our species evolved and it provides the essential resources needed to maintain our society. Understanding the processes by which the continental crust formed is one of the grand questions in geology. A clue to the origin of continental crust is its average composition. The crust's composition also factors prominently in determining the amount of heat producing elements that remained in the Earth's mantle after formation of the crust; these elements provide the energy needed to drive plate tectonics. Within the continental crust, most of the heat-producing elements are concentrated in the upper 10 km. Hence, determining the composition of the upper crust, and associated uncertainties, is crucial in understanding continental crust formation and evolution, as well as the energy balance of the Earth's interior.This project seeks insights into the composition of the upper continental crust through analysis of glacial sedimentary deposits from around the world. These deposits date from 2.9 to 0.3 Ga and provide insight into how the average composition of the Earth's upper crust has changed with time. The changing composition can, in turn, be used to infer the processes that formed the crust, as well as the changing conditions prevalent at the Earth's surface. The fine-grained matrix of the tillites will be analyzed for a comprehensive suite of major and trace elements and isotopic compositions. The effects of weathering and of changes in atmospheric composition on crustal composition will be assessed. These samples will form the basis of an upper crustal reference suite that will be made available to the community for further characterization of the upper continental crust through time.