DIMENSIONS OF THE LATE CRETACEOUS PALEOCENE NORTHEAST ATLANTIC RIFT DERIVED FROM CENOZOIC SUBSIDENCE

The distribution of Cenozoic subsidence across Northeast Atlantic volc anic margins have been evaluated to define the width of the rift zone and magnitude of extensional deformation. The subsidence profiles are corrected for the effects of lower-crustal magmatic bodies emplaced du ring continental break-up. The dimensions of the bodies have been deri ved from the crustal velocity structure. The width of the Late Cretace ous-Paleocene Northeast Atlantic rift zone was more than 300 km, and t he lithospheric extension factor increases gradually towards the line of continental separation. A large number of high-quality seismic refl ection data tied to scientific and commercial wells reveals that the i nitiation of extensional deformation preceded continental separation b y similar to 18 m.y. on the Voring margin, off Norway. These results s how that the Northeast Atlantic volcanic margins, commonly considered as typical volcanic margins indeed, have similar dimensions as non-vol canic margins, and as continental rifts. Thus, these margins contrast significantly with previously suggested evolutionary models based on n arrow rift zones and formation during rapid lithospheric failure. The wide rift is compatible with volume of igneous rocks observed along th ese margins, and with a thermal anomaly similar to that associated wit h production of Northeast Atlantic oceanic lithosphere.