Zircon Hf-isotope record for the evolution of the continental crust since 4.5 Ga

A worldwide database of over 16,000 combined U-Pb and Hf-isotope analyses of zircon, largely from detrital sources, has made it feasible to examine processes of crustal evolution on a global scale, and to test existing models for the growth of continental crust through time. Understanding the growth rate of the continental crust is critical in evaluating the proportion of juvenile material added to the crust at each point during its evolution. The amount of juvenile material produced at any given time is commonly underestimated, because some of that material was later reworked, and the record of the original juvenile material is buried or lost during subsequent crustal evolution. The approach proposed in this study attempts to account forthis effect, and "restore" an indication of the true juvenile input using the integrated dataset. The age data alone would support an Episodic Growth model, but the Hf-isotope data reveal that most of the magmatic rocks represented in the major "episodes" were derived by the reworking of pre-existing crust, especially after ca 2.5 Ga; the juvenile contribution represents a small proportion of most magmatic episodes. Modelling of the ages of the recycled components emphasises the repeated reworking of Archean components, supporting an Early Growth model. Furthermore, the large Hf-isotope datasets allow the definition of different patterns of continental crust generation in different tectonic settings, thus providing a basis for unraveling the global geodynamic evolution and supercontinent cycles of the ancient Earth.