Deep vs. shallow controlling factors of the crustal thermal field - insights from 3D modelling of the Beaufort-Mackenzie Basin (Arctic Canada)

Significant lateral variations in observed temperatures in the Beaufort-Mackenzie Basin raise the question on the temperature-controlling factors. Based on the structural configuration of the sediments and underlying crust in the area, we calculate the steady-state 3D conductive thermal field. Integrated data include the base of the relic permafrost layer representing the 0 degrees C-isotherm, public-domain temperature data (from 227 wells) and thermal conductivity data. For >75% of the wells the predicted temperatures deviate by <10K from the observed temperatures, which validates the overall model setup and adopted thermal properties. One important trend reproduced by the model is a decrease in temperatures from the western to the eastern basin. While in the west, a maximum temperature of 185 degrees C is reached at 5000m below sea level, in the east the maximum temperature is 138 degrees C. The main cause for this pattern lies in lateral variations in thermal conductivity indicating differences in the shale and sand contents of the different juxtaposed sedimentary units. North-to-south temperature trends reveal the superposition of deep and shallow effects. At the southern margin, where the insulating effect of the low-conductive sediments is missing, temperatures are lowest. Farther north, where the sub-sedimentary continental crust is thick enough to produce considerable heat and a thick pile of sediments efficiently stores heat, temperatures tend to be highest. Temperatures decrease again towards the northernmost distal parts of the basin, where thinned continental and oceanic crust produce less radiogenic heat. Wells with larger deviations of the purely conductive model from the temperature observations (>15K at 10% of the wells) and their basin-wide pattern of misfit tendency (too cold vs. too warm temperature predictions) point to a locally restricted coupling of heat transport to groundwater flow.