5 - The NE Atlantic conjugate margins

Abstract

By integrating seismic reflection and wide-angle refraction profiles, crustal velocities, and potential field data we construct composite structural maps for NE Atlantic (at present time and at distinct plate reconstruction stages within Cenozoic times) and a series of conjugate crustal transects across the main margin segments, and we study “total-rift”/conjugate margin formation processes. The sedimentary basins at the NW European margins, and their conjugates off Greenland, within the ~3000-km-long region between the Charlie-Gibbs Fracture Zone and Svalbard-NE Greenland developed as a result of a series of post-Caledonian rift episodes until early Cenozoic time, when complete continental separation took place. The lithospheric breakup was accompanied by massive, regional magmatism that led to the creation of the North Atlantic Volcanic Province. The compilation elucidates a pattern of margin segmentation, indicating the influence of structural inheritance, and the various segments are characterized by distinct crustal properties, structural and magmatic styles, and post-opening history of vertical motions. In a NE Atlantic conjugate margin setting, there are distinct along-margin symmetries and asymmetries in the distribution of the breakup-related volcanic rocks, and the well-defined first-order transfer systems appear to exert a major control on the tectono-magmatic processes. Within the NE Atlantic province, there is evidence for widespread Late Paleozoic-Early Mesozoic tectonism, but the structural margin configuration mainly evolved in response to the Late Jurassic-earliest Cretaceous rift episode. Structural and stratigraphic relations also indicate an Aptian-?Albian rift phase. The subsequent Late Cretaceous-Paleocene rifting, with onset in Campanian time, is characterised by prominent low-angle detachment structures and the rift may have reached a cross-margin width of 200-250 km and led to breakup at the Paleocene-Eocene transition. The line of breakup which is locally oblique with respect to pre-existing rift systems has further enhanced the along-margin asymmetries. After breakup, the passive margin evolved in response to subsidence and sediment loading during widening and deepening of the NE Atlantic Ocean. We refine a pulse of rapid progradation from the mainland in Oligocene, or alternatively Middle to Late Miocene, time and mid-Cenozoic intra-basinal doming in response to a regional compressive regime. The margin setting was changed in Late Pliocene when the Northern Hemisphere Glaciation led to rapid progradation forming a huge, regional depocentre near the shelf edge along the entire margin.