The Lofoten/Vesterålen land area is the only exposed basement high on the continental margin around mainland Norway. The onshore and offshore areas went through a rapid crustal cooling from temperatures higher than 550°C at maximum Caledonian metamorphism, through temperatures around 300-400°C in late Devonian/mid-Carboniferous, to surface temperature in mid-Jurassic. During the early to mid-Jurassic, a smooth, peneplained basement relief developed throughout the area. In mid-Jurassic, a period of normal faulting, subsidence and sedimentation was initiated and large parts of the Lofoten/Vesterålen off- and onshore areas subsided. Faulting occurred more or less continuously throughout the mid-Jurassic to early Cretaceous, but the largest fault movements took place during the early Cretaceous, presumably in Albian to Aptian times. During the early Cretaceous, the Lofoten Ridge developed as a horst while the surrounding areas (Vesterålen/Andøya and sedimentary basins) subsided below a several km thick Lower Cretaceous succession. The final rifting phase during late Cretaceous and Palaeocene was focused west of the Utrøst Ridge and Andøya, but minor faulting also occurred throughout the Andøya/Vesterålen/Lofoten area. During a late Cenozoic compressional phase the entire Lofoten and Vesterålen margin east of the present shelf edge was uplifted and eroded. The erosion and resulting isostatic uplift continued throughout the glacial period.
Helge Løseth, IKU Petroleum Research, N-7034 Trondheim, Norway.
Einar Tveten, Norges Geologiske Undersøkelse, Postboks 3006, N-7002 Trondheim, Norway.