Uniform heat flow in a deep hole in the Canadian Shield and its paleoclimatic implications

Precise temperature measurements to 2865 meters in a hole in a granitic pluton near FHn Flon, Manitoba, Canada, showed a systematic increase of temperature gradient with depth. Conductivity determinations at 50-meter intervals revealed a corresponding systematic decrease in conductivity. Over the entire measured depth, no systematic deviation from the mean heat flow of 1.01±0.04 μcal/cm2 sec is detectable in spite of strong evidence that the ground-surface temperature was at least 3.5°C cooler than at present for long periods during the Pleistocene epoch. These results can be reconciled with plausible paleoclimatic models. Evidently climatic change at this site does not result in a significant correction to the measured heat flow. The observations suggest that generalized estimates of the Pleistocene effect should be assigned a large uncertainty in the absence of an observed variation of heat flow with depth confirming a particular climatic model. The mean heat production is 2.1×10−13 cal/cm3 sec. Taken with the observed heat flow of 1.01 μcal/cm2 sec, it is consistent with other observations of heat flow and heat production in the stable interior of North America.