The basement geology of the Porcupine High – new geochronological constraints from the westernmost Caledonides

• The Porcupine High (PH) links the circum-Iapetus basement of NW Europe and Atlantic Canada. • Granitic basement (1.3 Ga) with high-temperature Grenville metamorphism identified. • Lower Dalradian metasedimentary cover exhibits very low-grade Caledonian metamorphism. • The Fair Head–Clew Bay Line (FHCBL) traced through north PH by geochronology and geophysics. • FHCBL igneous (500–481 Ma) and metasedimentary rocks show strong Acadian (425–415 Ma) overprint.