Simulating the thermochemical magmatic and tectonic evolution of Venus's mantle and lithosphere: Two‐dimensional models

Abstract

Numerical convection models of the thermochemical evolution of Venus are compared to present‐day topography and geoid and recent resurfacing history. The models include melting, magmatism, decaying heat‐producing elements, core cooling, realistic temperature‐dependent viscosity and either stagnant lid or episodic lithospheric overturn. In stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick crust, inconsistent with observations. Partitioning of heat‐producing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5–8 overturn events over Venus's history, each lasting ∼150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature ∼constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus‐like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth‐like but shifted to higher values. The basalt density inversion below the olivine‐perovskite transition causes compositional stratification around 730 km; breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature ∼rheological temperature scale lower than TCMBis not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start. Core heat flow decreases with time, possibly shutting off the dynamo, particularly in episodic cases.