The opening of the Arctic Ocean involved multiple stages of continental rifting and intrusion of extensive dykeswarms. To trace tectonomagmatic processes of the High Arctic, we present the first U–Pb ages for alkaline dyke swarms ofNorth Greenland. Concordia ages of 80.8 ± 0.6 and 82.1 ± 1.5 Ma indicate that north–south and east–west dykes are coeval.The north–south dykes reflect initial east–west rifting that led to break-up along the Gakkel Ridge and formation of theEurasia Basin. The east–west dykes reflect local variations in the stress field associated with reactivated Palaeozoic faults