Rejuvenation vs. recycling of Archean crust in the Gawler Craton, South Australia: Evidence from U-Pb and Hf isotopes in detrital zircon

Zircon grains from modern and ancient drainages of the Gawler Craton, South Australia have been analysed to define the relative contributions of juvenile sources and recycled crust to magmatic activity as a function of time, and to constrain the role of mantle inputs during the Proterozoic rejuvenation of the Archean Gawler Craton. The integration of Hf-isotope data with U-Pb age spectra shows that the crustal evolution was dominated by long periods of crustal reworking, and that crust generated in the Paleoarchean (3.2-3.5 Ga) was largely reworked during Proterozoic time. Four periods of juvenile mantle input can be recognised at ca 2540 Ma, 1853 Ma, 1595 Ma and 1169 Ma. The 1169 Ma event is not previously recognised in the Gawler Craton, but the absence of other important age peaks argues against the transport of these zircons from the Musgrave Block. Only minor proportions of the magmatic zircons with Paleoproterozoic to Mesoproterozoic ages have strongly juvenile signatures (εHf ≥ 4), indicating that crustal reworking was the dominant process, with relatively minor mantle input. Comparison of the crustal evolution with that of nearby Australian terranes suggests that although the Gawler Craton shows some similarities with the Mount Isa Block and the Georgetown Inlier in Neoarchean-Paleoproterozoic time, it evolved independently between ca 1800 and 1550 Ma.