Effects of radiogenic heat production and mantle compressibility on the behaviors of Venus’ and Earth’s mantle and lithosphere

Abstract

The effects of radiogenic heat production and mantle compressibility on the behaviors of Venus’ and Earth’s mantle and lithosphere are evaluated using a series of two-dimensional Cartesian numerical models with pressure- and temperature-dependent rheology. The main findings of the numerical model experiments are summarized as follows. 1) Radiogenic heat production increases the mean mantle temperature and strengthens the vigor of mantle convection. This increased mantle temperature reduces the thickness of the thermal lithosphere. If the radiogenic heat production of Venus is comparable to that of Earth, the mantle temperature in Venus’ deep lower mantle will be significantly increased. 2) Mantle compressibility weakens the vigor of mantle convection, especially in the deep lower mantle, and the thickness of the thermal lithosphere is increased as a result of the lower temperature of the upper mantle. Mantle compressibility generates additional mantle adiabat of approximately 0.14–0.25 K/km, comparable to the mantle adiabat of approximately 0.35 K/km generated by the adiabatic mantle compression. 3) Radiogenic heat production and mantle compressibility collaboratively contribute to the behaviors of Venus’ and Earth’s mantle and lithosphere. The additional mantle adiabat is linearly shifted by the additional heat of the radiogenic heat production. 4) Regardless of the radiogenic heat production and mantle compressibility, the Venus’ sluggish and Earth’ stagnant motion of the thermal lithosphere are inconsistent with their present-day immobile and mobile plate motions, respectively. The presences of water and volatiles, plastic rheology, extreme greenhouse effects, and/or transient mantle layering are essential for Venus’ and Earth’s characteristic evolutions.