Crustal evolution of the South Mayo Trough, western Ireland, based on U-Pb ages and Hf-O isotopes in detrital zircons

Ordovician strata of the South Mayo Trough in western Ireland contain clastic deposits that represent materials eroded from a large and diverse continental area over a time scale that spans much of the Earth's history. Therefore, it is a useful region to use detrital zircons to construct a continental crustal growth model. Here, we report integrated U-Pb, Lu-Hf and O isotope measurements obtained from in situ analyses of 160 zircons from the South Mayo Trough. U-Pb zircon crystallization ages define three major magmatic episodes of crustal reworking in the Archaean (Lewisian), Mesoproterozoic (Grenville), and Ordovician (Grampian). These data, together with oxygen isotope data and Hf model ages, suggest that crustal growth, recorded in the strata of the South Mayo Trough, started at c. 4 Ga and continued until 1.4 Ga, with two major growth periods at 2.3-2.1 and 2.0-1.5 Ga. We find that the crustal incubation time is decoupled from the duration of supracrustal alteration processes; some zircons with very long crustal incubation times have pristine mantle delta O-18 signatures suggesting minimal low-temperature surface processing in their source regions. Identifying such zircons is the key for future studies in constructing realistic net continental crustal growth models unaffected by crustal recycling.