Thermochronological Studies of High-Grade Metamorphism: The Grenville Terrane

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Garnet is a common metamorphic mineral in many medium and high-grade terranes. This project will explore the possibility that U, Pb, Nd and Sm are sufficiently immobile in garnet that if an age progression from core to rim of garnets can be observed, it may be equated to growth during active prograde metamorphism. If successful, garnet growth age information can be combined with geothermometry to follow the rate of temperature change during metamorphism. The project will evaluate the blocking temperatures for the diffusion of U, Pb, Nd and Sm in calcic and iron-rich garnets, and will examine zoned garnets from two well- studied areas of high grade metamorphism - the Grenville of Ontario and New York and the Archean Pikwitonei Domain of Manitoba. Results, if successful will provide a method to determine heating rates in high temperature metamorphism, a parameter that has considerable importance in orogenic studies but can not be measured or satisfactorily estimated at present.