Petrology and Geochronology of Metamorphic Zircon

Zircon is unusually well suited for investigating metamorphic processes because it is readily analyzed for U-Pb ages, it harbors diverse mineral inclusions, and its chemistry can be linked to metamorphic parageneses and P-T paths. Metamorphic zircon chemistry and ages are relevant only at the sub-grain micron scale, and consequently many analytical methods, such as depth profiling, have been developed to exploit such spatially resolute infor­mation. Here we review how metamorphic zircon grows, and how its chemistry and inclusion assemblages may be used to link the age of a zircon domain to its metamorphic P-T condition. Domain-specific ages and inclusion assemblages from ultrahigh-pressure (UHP) zircons constrain rates of subduction and exhumation. Textures and chemistry of zircon and garnet from high- and ultrahigh temperature (UHT) rocks reveal petrogenetic implications of deep crustal heating, melting, and melt crystallization. Trace elements, inclusion assemblages, and oxygen isotopes in zircon show that dehydration reactions may catalyze zircon growth during subduction. Future research should include identifying natural systems that constrain diffusion rates, determining crystal-chemical controls on trace element uptake in zircon and garnet for understanding how rare earth budgets and patterns change during metamorphism, and identifying underlying principles that govern the dissolution and reprecipitation of zircon during metamorphism.