| Abstract |
In order to understand the regional thermal regime beneath the northern North Sea and adjacent areas of the continent, a 3D thermal modelling has been applied in the framework of the Crustal Onshore-Offshore Project (COOP project). The lithosphere-scale 3D model has been used as a realistic approximation of the geometries of the sedimentary infill as well as of the underlying crystalline crust and lithospheric mantle during the 3D thermal modelling. Construction of the 3D model has been done by use of recently published/released structural data. For the upper part of the model, all available data were merged into the following layers: sea water, the Cenozoic, Upper Cretaceous, Lower Cretaceous, Jurassic, Triassic, Upper Permian (Zechstein) salt, Upper Permian clastics/carbonates and, finally, the Lower Permian-pre-Permian sedimentary rocks. The lithosphere-asthenosphere boundary has been determined from previously published data. Configuration of the crystalline crust and the Moho topography have been derived from the published interpretations of deep seismic lines and validated by a 3D density modelling. The 3D density modelling has been carried out by use of the software IGMAS+ (the Interactive Gravity and Magnetic Application System). According to the 3D density modelling, the crystalline crust of the study area consists of several layers. The obtained Moho is strongly uplifted beneath the Central and Viking grabens whereas the lithosphere-asthenosphere boundary is relatively shallow beneath the western part of the model area. The 3D thermal modelling has been performed by use of the commercial software package COMSOL Multiphysics. For the upper boundary, the time-dependent temperature at the Earth's surface and sea bottom has been applied. This has been done by taking into account palaeoclimatic changes during the last 200,000 years. The lithosphere-asthenosphere boundary has been chosen as a lower thermal boundary which corresponds to the 1300 °C isotherm. Results of thermal modelling within the upper part of the 3D model indicate that the mainland is generally colder than the basin areas. This regional trend of temperature is mostly related to the low thermal conductivity of sediments which increases heat storage within the areas covered by a thick sedimentary cover. Thick low-conductive sediments reduce the rate of heat transfer, acting as a thermal insulation. This thermal effect is especially pronounced within the Central and Viking grabens, and the East Shetland and Norwegian-Danish basins where the sedimentary cover is thickest. Furthermore, the effect of increased radiogenic heat production within the upper crust is prominent beneath the Horda Platform, where the highest geothermal gradient is modelled within the upper part of the 3D model. At great depths (70-100 km), the temperature distribution roughly reflects the configuration of the lower thermal boundary which is represented by the base of the lithosphere. |