40AR 39AR MINERAL AGE RECORD IN NE GREENLAND - IMPLICATIONS FOR TECTONIC EVOLUTION OF THE NORTH-ATLANTIC CALEDONIDES

40Ar/39Ar 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 40Ar/39Ar 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.