Description: High-resolution aeromagnetic surveys in the Nordkapp Basin, western Barents Sea, demonstrate the capability of modern, high-resolution aeromagnetic surveys to provide an efficient and promising tool for mapping features related to salt diapirism. Salt diapirs are clearly visible by a small, low-amplitude negative round to ellipsoidal magnetic pattern. This pattern coincides with shallow sedimentary layers deformed by the rising salt during active and passive diapirism. The dimensions of these features coincide in shape and size with those interpreted on gravity and seismic surveys.

Description: We propose a new, sunken continent beneath the North Atlantic Ocean that we name Icelandia. It may comprise blocks of full-thickness continental lithosphere or extended, magma-inflated continental layers that form hybrid continental-oceanic lithosphere. It underlies the Greenland-Iceland-Faroe Ridge and the Jan Mayen microplate complex, covering an area of ~600,000 km2. It is contiguous with the Faroe Plateau and known parts of the submarine continental rifted margin offshore Britain. If these are included in a “Greater Icelandia,” the entire area is ~1,000,000 km2 in size. The existence of Icelandia needs to be tested. Candidate approaches include mag- netotelluric surveying in Iceland; ultralong, full-crust-penetrating reflection profiling along the length of the Greenland-Iceland-Faroe Ridge; dating zircons collected in Ice- land; deep drilling; and reappraisal of the geology of Iceland. Some of these methods could be applied to other candidate sunken continents that are common in the oceans.

Description: The breakup of Laurasia to form the Northeast Atlantic Realm disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed that are underlain by magma-inflated, extended continental crust. North of the Greenland-Iceland-Faroe Ridge a new rift–the Aegir Ridge–propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge the proto-Reykjanes Ridge propagated north through the North Atlantic Craton along an axis displaced ~150 km to the west of the rift to the north. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed an ~300-km-wide transverse barrier. Thereafter, the ~150 × 300-km block of continental crust between the rift tips–the Iceland Microcontinent–extended in a distributed, unstable manner along multiple axes of extension. These axes repeatedly migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day in Iceland. It is the surface expression of underlying magma-assisted stretching of ductile continental crust that has flowed from the Iceland Microplate and flanking continental areas to form the lower crust of the Greenland-Iceland-Faroe Ridge. Icelandic-type crust which underlies the Greenland-Iceland-Faroe Ridge is thus not anomalously thick oceanic crust as is often assumed. Upper Icelandic-type crust comprises magma flows and dykes. Lower Icelandic-type crust comprises magma-inflated continental mid- and lower crust. Contemporary magma production in Iceland, equivalent to oceanic layers 2–3, corresponds to Icelandic-type upper crust plus intrusions in the lower crust, and has a total thickness of only 10–15 km. This is much less than the total maximum thickness of 42 km for Icelandic-type crust measured seismically in Iceland. The feasibility of the structure we propose is confirmed by numerical modeling that shows extension of the continental crust can continue for many tens of millions of years by lower-crustal ductile flow. A composition of Icelandic-type lower crust that is largely continental can account for multiple seismic observations along with gravity, bathymetric, topographic, petrological and geochemical data that are inconsistent with a gabbroic composition for Icelandic-type lower crust. It also offers a solution to difficulties in numerical models for melt-production by downward-revising the amount of melt needed. Unstable tectonics on the Greenland-Iceland-Faroe Ridge can account for long-term tectonic disequilibrium on the adjacent rifted margins, the southerly migrating rift propagators that build diachronous chevron ridges of thick crust about the Reykjanes Ridge, and the tectonic decoupling of the oceans to the north and south. A model of complex, discontinuous continental breakup influenced by crustal inhomogeneity that distributes continental material in growing oceans fits other regions including the Davis Strait, the South Atlantic and the West Indian Ocean.

Description: The Møre and Vøring basins of the mid-Norwegian volcanic passive margin are characterized by thick accumulations of Cretaceous to Paleocene sedimentary strata. They were formed during a series of Late Mesozoic-Early Cenozoic extensional events and represent vast underexplored areas with a limited number of wells. Recently, a new generation of long-offset 2D seismic reflection lines and 3D seismic data, together with new well data, has permitted a significant improvement in the regional understanding of the Møre and Vøring basins. This has enabled much better imaging of the deep Cretaceous subbasins and sub-basalt structures. In light of this significant data improvement, we performed a regional tectonostratigraphic synthesis of the pre-breakup development of the Møre and Vøring basins. We have interpreted eight regional Cretaceous and Paleocene horizons and constructed a series of structural and thickness maps. The new interpretations allow us to examine the sequential evolution of the Cretaceous to Paleocene sedimentary infill and to discuss its relationship to the deep crustal structures and regional tectonic events. We conclude that the long and polyphased development of the Møre and Vøring basins is partly controlled by deep-seated structural highs. We show that active deposition in the Early Cretaceous was mainly focused in the Møre Basin, while the main Cenomanian and subsequent Late Cretaceous-Paleocene depocentres developed principally in the Vøring Basin and migrated sequentially west towards the present continent-ocean boundary. We argue that the outer Møre and Vøring basins are likely underlain by a relatively thick continental crust compared to the inner part of the regional sag basin. In this setting our observations do not support evidence for a large zone of exhumed upper mantle, which has previously been proposed to have formed before magmatism and breakup.

Description: Three boreholes drilled during the International Ocean Discovery Program (IODP) Expedition 396 have yielded unexpected findings of altered granitic rocks covered by basalt flows, interbedded sediments and glacial mud near the continent‐ocean transition of the mid‐Norwegian margin. U‐Pb and K‐Ar geochronological analyses were conducted on both protolithic and authigenically formed K‐bearing minerals to determine the age of granite crystallisation and subsequent alteration episodes. The granite's crystallisation age based on 104 zircons is 56.3 ± 0.2 Ma, and subsequent exhumation along with alteration/weathering events took place between 54.7 ± 1 and 37.1 ± 1 Ma. This intrusion represents the youngest granite discovered in Norway and intruded at an extremely shallow crustal level before a rapid rift‐to‐drift transition. The shallow emplacement of granitic rock and its fast exhumation before and during the onset of volcanism holds significant implications for the syn‐ and post‐breakup tectonic evolution of volcanic margins.