Author name: Simon L. Harley

Using the U–Pb geochronology of zircon we can understand the growth and collapse of mountain chains, both recent and ancient. In the hightemperature metamorphic rocks that underlie mountain ranges, zircon may survive from precursor rocks, recrystallize, or grow anew. All these possibilities must be considered in the interpretation of zircon ages. Microtextural characterisation and microanalysis, coupled with considerations of mineral equilibria and trace element distributions between zircon and neighbouring silicate minerals, provide insights into the factors controlling zircon modification and growth. Zircon ages do not usually correspond to the peak of metamorphism but instead provide information on the history of cooling from high temperatures, including the timing and rates of exhumation of the deep roots of mountain chains.

Where would Earth science be without zircon? Tiny crystals of zircon occur in many rocks, and because their atomic structure remains stable over very long periods of geological time, they are able to provide a picture of the early history of the Earth and of the evolution of the crust and mantle. Zircon has long been recognized as the best geochronometer using the radioactive decay of uranium to lead. Recent developments in analytical techniques, using small-diameter laser, ion and electron beams, high-precision mass spectrometry and a variety of microscopic imaging methods, allow us to obtain the ages of tiny volumes of complex crystals that record stages in their long growth history. Coupled measurements of the isotopes of oxygen and hafnium provide a mineralogical window into the separation of the Earth’s crust from the mantle and the temperature and character of processes involved in crustal evolution. Zircon is being used to unravel ever more complex geological systems, presenting exciting opportunities for research on this remarkable mineral.