The Implications of Terrestrial Heat Flow Observations on Current Tectonic and Geochemical Models of the Crust and Upper Mantle of the Earth

The average heat flow through continental orogenic belts decreases with the age of the orogeny to an approximately constant value for the Precambrian shields and platforms. The average heat flow for provinces of the North Pacific decreases with the age of the province. The mean heat flow through the province younger than 10 million years is 2.82 p cal cm-2 -1 whereas the mean heat flow through provinces older than the middle Cretaceous is 1 . 1 5 ~ cal cm-2 s-'. The contrast in the chemical composition of continental and oceanic crustal rocks and the disparity in time scale for the decay of heat flow suggest a different explanation for the heat flow through oceans and continents. The observed equality of the mean oceanic and continental heat flows may not be relevant to evaluating the thermal contribution of the upper mantle.