Late Carboniferous-Permian tectonics and magmatic activity in the Skagerrak, Kattegat and the North Sea

Abstract

This study focuses on Late Carboniferous-Permian tectonics and related magmatic activity in NW Europe, and specifically in the Skagerrak, Kattegat and North Sea areas. Special attention is paid to the distribution of intrusives and extrusives in relation to rift-wrench geometries. A large database consisting of seismic and well data has been assembled and analysed to constrain these objectives. The continuation of the Oslo Graben into the Skagerrak has been a starting point for this regional study. Rift structures (with characteristic half-graben geometries) and the distribution of magmatic rocks (intrusives and extrusives) were mapped using integrated analyses of seismic and potential field data. For the analysis of the Sorgenfrei-Tornquist Zone and the North Sea, seismic and well data were used. The rift structures in the Skagerrak can be linked with extensional structures in the Sorgenfrei-Tornquist Zone in which similar fault geometries have been observed. Both in the Skagerrak and in the Kattegat, lava sequences were erupted that generally parallel the underlying Lower Palaeozoic strata. This volcanic episode, therefore, pre-dates main fault movements and the development of halfgrabens filled with Permian volcaniclastic material. Upper Carboniferous-Lower Permian extrusives and intrusives have also been found in wells in the Kattegat, Jutland and the North Sea (Horn and Central grabens). Especially in the latter area, the dense seismic and well coverage has allowed us to map out similar Upper Palaeozoic geometries, although the presence of salt often conceals the seismic image of the underlying strata and structures. From the results, it is assumed that the pre-Jurassic structures below large parts of the Norwegian-Danish Basin and northwards into the Stord Basin on the Horda Platform belong to the same tectonic system.

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

“…Moreover, the location of the modelled Permian intrusion in that area (Fig. 12A) together with the already mentioned Permian magmatic rocks within the northeastern part of the North Sea (Evans et al, 2003;Heeremans & Faleide, 2004), support at least in part a Late CarboniferousEarly Permian origin for the anomalously thickened high-density lower crust beneath the Northern Permian Basin. However, a Sveconorwegian or even older age for the thickening of the high-density lower-crustal layer cannot be excluded in this part of the 3D model.…”

“…The study area was affected by a regional-scale Late Carboniferous-Early Permian rifting event with deposition of relatively thick clastic sediments (Plein, 1990;Ziegler, 1990;Abramovitz & Thybo, 1999;Stemmerik et al, 2000;Heeremans & Faleide, 2004) and was followed by precipitation of a large amount of Upper Permian evaporites, represented by mainly rock salt and anhydrite (e.g., Masytrenko et al, 2012Masytrenko et al, , 2013. During post-Permian time, the Upper Permian salt has been reactivated to form various salt structures during the Meso-Cenozoic tectonic events, strongly complicating the internal structure of the sedimentary cover within the Central Graben and the Norwegian-Danish Basin.…”

“…If the Sveconorwegian parameters of the paleomagnetic field (declination 293° and inclination 64°) are used, the intrusion has to be represented by two combined, southward-dipping, low-magnetic and high-magnetic bodies as according to the previous attempt with the help of 2.5D magnetic modelling by Olesen et al (2004) who assumed that this intrusion is a part of the Sveconorwegian Rogaland Igneous Province. The Skagerrak Graben is interpreted as a dry rift with a small volume of magmatic rocks (Heeremans & Faleide, 2004). The mafic rocks of the Rogaland Igneous Province do, in general, show up as negative magnetic anomalies, whereas the felsic rocks have positive anomalies.…”

“…Voluminous magmatic bodies with reverse magnetisations are not known from the Oslo Rift. According to drilling data (Smelror et al, 1997;Evans et al, 2003;Heeremans & Faleide, 2004), Permian volcanic rocks have not been encountered by any boreholes in the Farsund and Skagerrak grabens in the Norwegian sector of the North Sea; nor has there been observed any Permian volcanic rocks along the coast immediately to the north of the offshore intrusion. All these facts about the missing Permian magmatic rocks in the surrounding area allow us to suggest that a Sveconorwegian magmatic intrusion is a viable alternative to the Permian model age suggested by Åm (1973).…”

Upper-mantleP- andS-wave velocities across the Northern Tornquist Zone from traveltime tomography

“…Heeremans & Faleide 2004) which, according to Torsvik et al (2008), have the characteristics of a Large Igneous Province (LIP) centred on the Skagerrak Sea (Skagerrak-Centered LIP: SCLIP). Both the Danish Basin and the North German Basin were initiated in relation to these magmatic and tectonic events.…”