40 Ar/ 39 Ar mineral age record in NE Greenland: implications for tectonic evolution of the North Atlantic Caledonides

40 Ar/ 39 Ar mineral ages have been determined from basement gneisses and cover sequences exposed in the Caledonides of NE Greenland. These range between c . 438 Ma and c . 370 Ma (early Silurian-mid-Devonian).They are interpreted as dating cooling following polyphase Caledonian metamorphism which completely reset argon systems within the (early Proterozoic) basement gneisses. The 40 Ar/ 39 Ar results indicate that thrust-related regional deformation and metamorphism in NE Greenland continued into the early Devonian. This contrasts with Scandinavia, where nappe stacking was largely completed by the early–mid-Silurian and was followed by regional extension and tectonic unroofing in the late Silurian–mid-Devonian. Tectonic models developed for the late-orogenic evolution of the northern Atlantic Caledonides therefore need to incorporate considerable along- and across-strike variation in both the style and timing of major tectonothermal events.