Laurentian origin of the Ordovician Grangegeeth volcanic arc terrane, Ireland

<p>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 (<em>n</em> = 24) yields an age of 465.4 +2.4/−3.1 Ma. Inherited zircons yield ages of <em>c</em>. 1120–1520, <em>c</em>. 1650–1914 and <em>c</em>. 2540–2890 Ma. The absence of zircons between <em>c</em>. 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. </p>