Erosion and the age dependence of continental heat flow

Summary. Erosion of continental crust has two effects on surface heat flow: a decrease due to the removal of heat‐producing elements, and an increase due to the movement of hot rock towards the surface. In an orogenic belt, where erosion may remove tens of kilometres of material, these effects are important over time‐spans comparable with the life of the belt as an elevated region. An expression is derived which relates surface heat flow to time, heat flow through the deep lithosphere, the distribution of heat sources and the amount and time constant of erosion. The variability of crustal processes permits wide ranges of values for these parameters and geologically reasonable parametral combinations can readily be found which satisfy the surface heat flow observations. These combinations can account for the long time‐scale of surface heat flow decay, and the influence of erosion on ‘reduced’ heat flow has important consequences. This approach predicts a relationship between reduced heat flow and age which is close to that observed, and a linear relation between surface heat flow and reduced heat flow similar to that reported by Pollack & Chapman. The intercept on q 0 – A 0 plots (the reduced heat flow) has a physical meaning which changes with time and should not be interpreted as, for example, the heat flux across the Moho. We conclude that an important part of the observed variation of surface heat flow with age may be explained by the effects of erosion and the variability of crustal processes. In its range of greatest variation surface heat flow mainly reflects these crustal processes and should not be used to infer directly the thermal development of the subcrustal lithosphere.