Depletion of Heat Producing Elements in the Martian Mantle

Abstract

Heat is primarily generated in planetary interiors by the decay of long‐lived heat producing elements (HPE). Planetary heat flow estimates can thus provide critical insights into the thermal state of a planet and the bulk distribution of the HPE. The lack of appreciable lithospheric deflection in the north polar region of Mars by the weight of the polar ice cap is suggestive of low heat flow. Here we model the deflection of the Martian lithosphere and show that the present‐day mantle heat flow cannot exceed 7 mW m in the north polar region of Mars. Our mantle heat flow estimate is notably lower than the heat flow expected from a chondritic mantle suggesting the Martian mantle to be depleted in HPE. If our result is globally representative, lower levels of heat generation in the planet s mantle may have inhibited widespread late‐stage volcanism on Mars. Plain Language Summary The geophysical evolution of a planet is governed by the rate of heat production within the planet and the mechanism and efficiency through which that heat is lost. After the accretion and differentiation of a planet, the major source of internal heat generation is through the decay of long‐lived radiogenic elements such as uranium, thorium, and potassium. We constrain the present‐day thermal structure in the north polar region of Mars by modeling observed geophysical flexure beneath the north polar cap. Our results suggest that most of the heat producing elements on Mars may be sequestered in the crust and that the mantle is depleted in these elements. If globally representative, our results have important implications for the thermal and geological evolution of Mars.