Hot spot heat transfer: Its application to Venus and implications to Venus and Earth

Abstract

Gross similarities between earth and Venus suggest that both planets might be expected to lose heat by the same mechanism. Available data do not resolve plate tectonics on Venus, however, and other heat loss mechanisms, such as hot spot heat loss, have been suggested. Using a model which gives a relationship among surface elevation, lithospheric thickness, and heat flux, we test the hot spot heat loss mechanism for Venus and determine that it can easily explain the predicted heat loss of the planet with a modest number of hot spots (of the order of 35). Approximately 93%of the mapped topography of Venus can be explained solely on the basis of lithospheric thickness variations. Additional compensation is required for topography above a radius of 6053 km, and this can be effected by incorporating a variable thickness crust into the model. If crust is assumed to be generated on the crests of the hot spots, probably by processes associated with volcanism, the model is consistent with almost 99% of the mapped Venus topography. The model is also basically consistent with available gravity data and interpretations which indicate compensated topography and great depths of compensation (100–1000 km) for the mid‐latitudes of the planet. The remaining approximately 1% of the topography not explained by hot spot crustal generation is thought to be compensated at a shallower depth primarily by variations in crustal thickness which are not directly related to hot spot volcanism. The models, relating surface elevation to lithospheric thickness and heat flow, are grossly consistent with either a plate tectonic or hot spot heat loss mechanism for Venus. The range of lithospheric thicknesses implied by the range of elevations on Venus implies that if plate tectonics is the dominant heat loss mechanism on Venus, the mean plate velocities are slower than on earth. Slow spreading ridges should be resolvable by the available Venus topographic data but are not apparent. Comparison and analysis of the hypsometric curves for earth and Venus suggest basic differences between the curves, the skewed terrestrial ocean floor curve being consistent with plate tectonics, but the relatively symmetrical venusian curve indicates that either plate tectonics differs on Venus from the terrestrial analogue or that plate tectonics does not dominate the topographic expression of Venus tectonism. The venusian curve is consistent with a hot spot heat loss mechanism. A hot spot crustal genesis mechanism is proposed which would probably result in crust very similar to the granite‐greenstone terranes of many terrestrial Archaean cratons. We speculate that hot spot heat loss may have preceded plate tectonics as the dominant terrestrial heat loss mechanism.