Laurentian origin of the Ordovician Grangegeeth volcanic arc terrane, Ireland

U-Pb ages determined by laser-ablation multi-collector inductively coupled plasma mass spectrometry on 199 zircons from a lithic pumice tuff are the first isotopic ages from the Grangegeeth volcanic terrane of Ireland. The youngest zircon population (n 1/4 24) yields an age of 465.4 +2.4/23.1 Ma. Inherited zircons yield ages of c. 1120-1520, c. 1650-1914 and c. 2540-2890 Ma. The absence of zircons between c. 550 and 700 Ma argues against involvement of Avalonia as a source of inherited crystals. Overall, the inherited age spectra are characteristic of Laurentian crust or metasedimentary successions of peri-Laurentian provenance. These findings suggest that the Grangegeeth volcanic terrane does not represent a continuation of the intra-Iapetus Exploits arc of Newfoundland.