Martin Guitreau

Crystallization and Disturbance Histories of Single Zircon Crystals From Hadean-Eoarchean Acasta Gneisses Examined by LA-ICP-MS U-Pb Traverses

Zircon U-Pb geochronology is a very robust dating method but the accuracy of determined ages can sometimes be compromised. This is because, as commonly observed, the U-Pb isotope system can be reopened during the post-crystallization evolution of a zircon. The present manuscript investigates the capability of traverses by LA-ICP-MS to identify zones of well-preserved U-Pb isotope systematics within zir- con crystals. The data for the different zones can be used to construct internal Discordia lines that provide age information about crystallization and metamorphism of single zircon crystals. To test our approach, we analyzed zircons from three ca. 3.96 Ga Acasta gneisses. Results demonstrate that such a method allows retrieval of original crystallization age in most of the studied zircons, even in those that experienced ancient U-Pb disturbances resulting in discordant U-Pb data. It was also possible to estimate disturbance ages, though not as precisely as for the igneous crystallization, in many of the studied crystal