Numerical analysis of the role of radiogenic basement on temperature distribution in the St. Lawrence Lowlands, Quebec

Regions with low or medium surface heat flow in stable cratonic areas, such as in eastern Canada, have received little attention for geothermal energy. In the presence of a high heat-producing basement overlain by a sedimentary cover, however, such areas might be prospective. Their potential will depend on various parameters such as heat production within the basement, thermal conductivity of sedimentary formations, and structural context. In this study, we aim at quantifying the importance of these parameters on temperature distribution at depth for a model representative of the St. Lawrence Lowlands, Quebec, where locally anomalously higher heat flow has been observed and a 3D model of sedimentary cover is available. Scenarios involving physical properties from neighbouring Grenvillian domains are considered: Portneuf-Mauricie domain with radiogenic heat production of 0.94-5.83 W<mml:mspace width="0.333333emm-3, 0.02-4.13 Wfor the Morin Terrane, and 0.34-1.96 Wm-3 for the Parc des Laurentides domain. The impact of radiogenic heating on temperature distribution at depth was simulated using the Underworld2 numerical modeling code. Results show that at 5 km depth, the range of temperature difference is 22 degrees C for all modeled scenarios. In addition, the benefit of the thermal blanket effect of the sedimentary cover can be significant, but depends strongly on the contrast in thermal conductivity between the basement and the cover, as well as on the structural context, and less on heat production in the basement. Finally, depth of the 120 degrees C isotherm varies by up to 1 km for the scenarios considered; carefully assessing the boundary conditions therefore, appears critical in an exploration context.