Zircon Exsolution from Rutile: Constraints on Ultra-High Temperature: Metamorphism of Lower Crustal Granulites

Zircon exsolution from rutile in ultra-high temperature (UHT; \u3e1000°C) lower crustal granulite xenoliths from South Africa provides a record of the evolving conditions of extreme metamorphism of continental crust. Scanning electron microscopy of rutile grains shows several types of zircon exsolution. Three distinct rutile grain types were identified: homogenous rutile grains with little to no zircon exsolution, mostly homogenous rutile grains with embayments of zircon-rutile intergrowth, and rutile grains with zircon exsolution lamellae in crystallographic or shape preferred orientations. We hypothesize these various reaction textures of zircon unmixing from rutile are related to the temperatures and the locations at which the rutile crystals grew and reacted during the metamorphic evolution of the granulite. Through detailed analysis of hundreds of rutile grains we plan to correlate the exsolution reaction textures with quantitative Ti and Zr concentrations and U-Pb geochronology in both mineral phases to build a time-temperature history of UHT metamorphism