Using Hf isotope model ages, it was possible to refine our crustal growth model. The pooled frequency distribution of Hf model ages from the GDZDb is multi-modal and similar in shape to the global pooled detrital zircon U-Pb age distribution with strong peaks present at 2.7-2.5, 2.0-1.7, 1.2-1.0, and 0.3-0.1 Ga and a weak peak at 0.7-0.5 Ga.
One approach is to observe the Hf model age distribution of a single age class (or peak) from the U-Pb database. For example, the 2.5-2.7 Ga peak in the U-Pb database exhibits a peak in Hf at 2.9-2.8 Ga. This suggests that the majority of grains observed formed during a 2.9-2.8 Ga event and were subsequently recycled and reset to 2.7-2.5 Ga (U-Pb age). The 2.0-1.7 peak from the U-Pb distribution exhibits two peaks in the Hf distribution (1.8 and 2.3-2.4 Ga). These two peaks suggest that zircons making up the 1.8 U-Pb peak were derived from two sources: recycled pre-existing grains (formed at 2.3-2.4 Ga) and younger grains that formed during the 1.8 Ga event.
Combining Hf data with the U-Pb age data provides constraints on whether crustal growth was juvenile (newly formed), recycled from pre-existing crustal materials, or a combination of the two processes. This dataset suggests that the prominent U-Pb peaks are dominated by grains derived from crustal recycling.