DEEP CONTROL ON SHALLOW HEAT IN THE CENTRAL EUROPEAN BASIN SYSTEM

Geothermal heat may be an attractive source for a future sustainable supply of energy. However, a regional assessment of geothermal resources involves an improved understanding of the main physical mechanisms involved in the transport of heatin the subsurface. We present results from 3D numerical simulations of conductive heat transport for the Central European Basin System (CEBS). This basin system covers the northern part of Central and Western Europe and contains more than 12 km thick sediments including a layer of strongly mobilized Upper Permian (Zechstein) salt. We use a 3 D structural model of the area that resolves the configuration of the basin fill, of the crust and of the lithospheric mantle to evaluate the relative influence of different depth levels on the shallow thermal field. We assess the sensitivity of the results with respect to variations in contrasting thermal rock properties of the sediment fill and with respect to the influence of different configurations of the crystalline crust and lithospheric mantle. We find that assuming conductive heat transport as the dominant mechanism predicts observed temperatures amazingly well. Our results indicate that lithosphere-scale factors controlling the temperature distribution are superposed with effects resulting from the spatial interaction of thermal rock properties. In particular, the structural complexity in response to the presence of salt diapirs, walls and pillows has decisive influence on the pattern of temperature distribution in the upper 8 km of the crust. These short- wavelength temperature variations (up to a few kilometers) are mainly influenced by the thickness and geometry of the thermally highly conductive salt layer. Accordingly salt structures are characterized by both positive thermal anomalies and increased heat flow above and negative anomalies within and below salt structures. In addition, this “chimney effect” of the salt is counteracted by the insulating effects of low-conductive clastic sediments in salt-rim synclines. In contrast, the long wavelength character (> 50 km) of the heat flow and temperature distribution is controlled by the configuration of the crystalline crust and upper mantle beneath the basin system.