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

Abstract

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 δ 18 O 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. Supplementary materials: Data tables for U–Pb, Lu–Hf and oxygen isotopes for detrital zircons from South Mayo Trough, as well as plots of values for zircon standards (δ 18 O for R33, U–Pb ages for 91500 and R33, and 176 Hf/ 177 Hf for 91500, GJ-1, and Plešovice) and reverse concordia plots of zircon samples are available at www.geolsoc.org.uk/SUP18543 .