Principal tectonic events in the evolution of the northwest European Atlantic margin

Abstract

The Atlantic margin of the Norwegian, Faeroese, British and Irish sectors encompasses numerous basins which vary in character, but are related in terms of their evolution as part of a single passive margin. Lineament analysis of the margin shows a predominance of NE–SW, N–S and NW–SE trends, mainly reflecting Mesozoic–Cenozoic extensional faulting. Some major Precambrian and Caledonian structures, principally steeply-dipping shears, were opportunistically reactivated according to the prevalent stress pattern. The extensional history of the margin spanned ac.350 Ma interval between the close of the Caledonian orogeny and early Eocene break-up. Episodes of Permo-Triassic, (mainly late) Jurassic, Early Cretaceous, ‘middle’ Cretaceous and latest Cretaceous–Early Eocene age can be distinguished from one another in space and time. The anomalous length of the total period of extension prior to continental separation is partly explained by step-wise lateral offsets of the crustal thinning axes towards the line of eventual break-up. The picture is, however, complicated by some changes in extensional style and direction. These include mosaic-like fragmentation of Pangea in the Permo-Triassic, the imposition of more systematic E–W extension by Jurassic times, and the change to NW–SE extension focused on the present margin in the Early Cretaceous (probably Hauterivian). The resulting structural configuration reflects the overprinting of a complex network of Jurassic and older basins by a continuous NE–SW chain of deep Cretaceous-Cenozoic basins. An extensional pulse of latest Cretaceous to earliest Eocene age (best observed in the Norwegian Sea) with extensive basaltic volcanism led to continental break-up at approximately 53 Ma.The margin was structurally modified by some important events postdating the Early Eocene. On breakup, the background stress field changed from extension to mild SE-directed compression, and widespread inversion structures formed in the thick Cretaceous-Cenozoic depocentres. The inversions can best be explained by ridge-push from the adjacent spreading centres, but could also be linked to Tethyan closure events and changes in the North Atlantic spreading vector. Post-break-up extension of the North Atlantic passive margins has been reported in the western Barents Sea, Jan Mayen and East Greenland and (for the first time here) in the northern Vøring Basin. We propose that these areas were linked by a single extensional pulse induced by the change to a more ESE-directed relative plate motion in the Oligocene-Miocene.Major uplift and exhumation of peripheral landmasses and inboard basins took place at intervals throughout the Cenozoic. Initial uplift can be attributed to pre-break-up rifting and post-break-up compression, but the most significant event took place in the Plio-Pleistocene and was intimately associated with glacial erosion and isostatic adjustment through repeated glaciations and interglacials. The regional scale of this event and its significance for exploration is widely under-estimated.

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

“…Thermal modelling based on apatite fission track and (U-Th)-He data indicates significantly slower cooling rates since the Mid Jurassic, or even minor sedimentary burial of the coastal regions (Ksienzyk et al, 2014). At some time during the Late Jurassic to Early Cretaceous, the stress field for the North Sea region changed from E-W extension to NW-SE extension (Bell et al, 2014, and references therein) and active rifting shifted from the mostly N-S-oriented Viking Graben to the NE-SW-oriented future North Atlantic, culminating in the Early Eocene in continental breakup (Doré et al, 1999).…”

“…1) formed during a two-stage rift history, with an initial, wide Permo-Triassic rifting followed by a Mid-Late Jurassic rift phase that was focused mainly in the Viking Graben (e.g., Badley et al, 1988;Gabrielsen et al, 1990;Steel & Ryseth, 1990;Faerseth, 1996;Bell et al, 2014). In the Early Cretaceous, rifting was abandoned in most of the North Sea and instead became focused along the future North Atlantic, which experienced important rift stages in the Early Cretaceous, Mid Cretaceous and Palaeocene, culminating in continental breakup in the Early Eocene (Doré et al, 1999). An abundance of highquality seismic data allows the mapping of offshore fault systems in detail.…”

Extension, hyperextension and mantle exhumation offshore Norway: a discussion based on 6 crustal transects

“…There has been some controversy over whether this evolution should be viewed as one combined event or separated into distinct Late Jurassic and Early Cretaceous events (Lundin & Doré, 1997;Doré et al, 1999;Faleide et al, 2008). The problem is not easily resolved due to the lack of well control in the deep basins.…”

Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

“…The protracted extensional history of the region and superposition of NE Atlantic rifting on Paleozoic rift systems, themselves influenced by Caledonian and/or older fabrics, mean that pre-existing structural weaknesses are likely to be widespread along the margin (e.g. Doré et al, 1999), and the style of segmentation appears to vary considerably. Although the controls on segmentation style in the NE Atlantic are beyond the scope of this study to investigate, it is nevertheless important to consider the potential role of factors such as pre-existing structures, strain rate, or crustal thickness when applying any single model to the entire margin.…”