Mantle heat flow

A map of the heat flux out of the earth's mantle has been prepared by subtracting the heat flow arising in the earth's crust from the surface heat flow. In continental areas the crustal contribution of the enriched zone is determined from the parameters of the linear heat flow-heat production relationship q0= q*+ bA0in areas where such data exist. Where heat flow-heat production data are not available, a new empiricism relating reduced heat flow q*to the mean heat flow of a province ¯q0, q*≈ 0.6 *q0, is used to estimate the reduced heat flow, and the depth parameter bis assigned an average value of 8.5 km. The oceanic crustal heat flow contribution includes both heat liberated by cooling, which is a function of the age of the ocean floor, and a small radiogenic component. A spherical harmonic analysis to degree 18 of the computed 5° × 5° mantle heat flow values yields a mean of 48 mW m−2; the degree variance spectrum has prominent strength at degrees 1,4 and 5. Continent-ocean differences are more apparent in the mantle heat flow than in the surface heat flow. However, contrasting surface heat flow patterns within continents, such as in central and western Australia, which arise from different surficial radioactivity distributions, do not appear in the mantle heat flow. Mantle heat flow is positively correlated with the geopotential and negatively correlated with the topography of the earth. However, correlation of heat flow with a “normalized” topography, in which the base line elevation difference between oceans and continents is suppressed is significantly positive, in accordance with observation that ocean floor topography is thermally controlled.