Understanding the roles of crustal growth and preservation in the detrital zircon record

Crustal evolution studies using detrital minerals must consider the potential for bias introduced at the time of formation of the continental crust, through its preservation in subsequent supercontinental cycles and during erosion and reworking of sedimentary material. To investigate the extent of these biases, and our ability to extract global information from local studies, this study presents in situ U–Pb, O and Hf isotope data in detrital zircons from the Scottish Highlands for comparison with greater Gondwana and Laurentia. Zircon crystallisation ages range from 3.8–1.1 Ga, and they group into three episodes (at ∼ 2.8, 1.8 and 1.2 Ga), peaking within 100 Ma of the ages of known supercontinents (Superia, Nuna and Rodinia). They are therefore consistent with preservation due to continental collision and supercontinent stabilisation. The Hf model ages fall between 4.2–1.4 Ga, and they also group into three significant juvenile extraction events at ∼ 3.3, 2.2 and 1.7 Ga, of which only the ∼ 3.3 Ga peak has been observed elsewhere in Laurentia or Gondwana. There is a link between the distribution of U–Pb crystallisation ages and model Hf ages indicating typical residence times of ∼ 600 Ma between the formation of new crust and its reworking in later magmatic events. Individual Hf model ages appear to form continua within each crystallisation event, suggesting that the generation of new continental crust is a continuous process, even though the record is then biased by the development of supercontinents.