Deep structure of the northern North Sea and southwestern Norway based on 3D density and magnetic modelling

Abstract

The deep structure of the northern North Sea and the adjacent Norwegian mainland has been analysed by integrating all available structural data in combination with 3D density and magnetic modelling into a lithosphere-scale 3D structural model. The modelled configurations of the sedimentary cover and crystalline crust are consistent with the long-wavelength components of the observed gravity and magnetic fields over the study area. The first-order configurations of the top of the crystalline basement and the Moho topography have been obtained. According to the 3D density modelling, the low-density upper-crustal block beneath the Horda Platform has been shown to indicate a possible presence of metasedimentary and/or fractured granitic rocks. Possible remnants of island arc chains within the central part of the North Sea between the Laurentian and Baltican crustal domains are supported by the modelling. Moreover, based on the results of the 3D magnetic modelling, the 3D density/structural model has been differentiated into smaller crustal blocks with different magnetic properties, implying that these magnetically derived crustal blocks most likely differ lithologically from the rest of the initial density-based larger layers. Within the mainland, most of the crustal blocks with increased magnetic susceptibility are related to granitic and/or granodioritic rocks which are well mapped at the surface according to geological data. A prominent middle-upper crustal magmatic intrusion has been modelled within the northern part of the NorwegianDanish Basin. The local magnetic pattern supports a possible Permian age for this intrusion, whereas the regional magnetic pattern and known geology from the mainland indicate a Sveconorwegian origin as a more viable alternative. At the mantle level, a low-density lithospheric mantle has been modelled beneath NW Norway and adjacent offshore areas, reflecting the likely presence of an upper-mantle low-velocity zone there.

The Influence of Structural Inheritance and Multiphase Extension on Rift Development, the NorthernNorth Sea

“…Further north, where such granitic material is either not present, or alternatively not uplifted in the footwall of a shear zone, strain is more uniformly distributed, forming a single, wide rift (Figures and b). Although we are unable to directly image the crustal structure in this area to test this hypothesis, the 3‐D crustal model of Maystrenko et al (), although at a relatively coarse resolution, indicates thinned lithosphere beneath the Horda Platform and slightly thicker lithosphere beneath the Utsira High, in agreement with the model‐driven hypotheses presented here.…”

“…In the northern North Sea, the southern extension of the otherwise N‐S striking Øygarden Fault rotates to a NE‐SW orientation and locally aligns with the NE‐SW striking Hardangerfjord Shear Zone, suggesting a local NE‐SW oriented stress field associated with the shear zone (Figures and ). The Hardangerfjord shear zone represents a major structure across the northern North Sea rift and is associated with a Moho offset at depth (Gabrielsen et al, ; Maystrenko et al, ). Similarly, faults defining the western margin of the Stord Basin follow the underlying Utsira Shear Zone in plan‐view, rotating from N‐S in the south to NE‐SW further north.…”

“…This structure has an enhanced influence throughout the multiphase evolution of the rift compared to other interpreted Devonian shear zones. One possibility is that the Lomre Shear Zone extends to greater (i.e., midcrustal) depths, or that it reactivates a Caledonian or earlier structure, both of which have been proposed for the Hardangerfjord Shear Zone further south, which also exerts a different influence over rift physiography, being associated with a Moho offset at depth and controlling the location and geometry of the rift‐bounding faults in the Ling Depression (Fossen et al, ; Fossen & Hurich, ; Gabrielsen et al, ; Maystrenko et al, ). The Lomre Shear Zone has been proposed to represent the southern extension of the Nordfjord‐Sogn Detachment by Færseth et al (), although it does not appear to correlate with the structure onshore (Figure ).…”

Deciphering channel networks from aeromagnetic potential field data: the case of the North Sea Quaternary tunnel valleys

“…This study targets the high-frequency magnetic anomalies in order to characterize potential signatures of the channel structures. To proceed to the extraction of the high-frequency anomalies, we have modelled the long-wavelength anomalies on the basis of an E-W regional 2-D magnetic model (Maystrenko et al 2017, their fig. 21) that shows the configuration of the crustal structure in the southern part of the study area (xx' in Fig.…”

3-D seismic images of an extensive igneous sill in the lower crust

“…The study area is located in the northern North Sea (Fig. 1), where continental crust consists of 1030 km thick crystalline basement overlain by up to 12 km of sedimentary strata deposited during, after, and possibly even before periods of Late Permian-Early Triassic and Middle Jurassic-Early Cretaceous rifting (e.g., Bell et al, 2014;Maystrenko et al, 2017). The crystalline basement formed by terrain accretion during the Sveconorwegian (1140-900 Ma) and Caledonian (460-400 Ma) orogenies (Bingen et al, 2008).…”