Some geophysical implications from gravity and heat flow data

Abstract

The negative correlation coefficient, −0.82, between Izsak's satellite geoid and Lee and MacDonald's heat flow distribution suggests a correlation between the geoidal undulations and the highs and lows of heat flow, in the sense that depressions on the geoid correlate with regions of high heat flow while rises on the geoid correlate with regions of low heat flow. This implies that the depressions on the geoid are related to hotter and lighter material in the interior of the earth and the rises on the geoid are related to colder and heavier material. Assuming that the density anomaly Δρ, which is responsible for the geoidal undulations, is related to a temperature perturbation ΔT by Δρ/ρ = −αΔT, where α is the coefficient of thermal expansion, and that ΔT is caused by an inhomogeneous distribution of radiogenic heat sources, the location of this distribution of heat sources is found within the outer 100 to 200 km of the mantle, and the corresponding temperature variation has a maximum amplitude of about 100°C. The corresponding fluctuation of radiogenic heat is about ±1 to ±2×10−14 cal/cm3 sec, which implies that the upper mantle contains much stronger heat sources than does peridotite or dunite. An eclogitic upper mantle seems, in this respect, more likely.