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

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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.