On the relative importance of thermal and chemical buoyancy in impact-induced melting on Mars

Kurzfassung

We ran series of 2D numerical mantle convection simulations of the thermochemical evolution of a Mars-like planet. In order to study the importance of compositional buoyancy of melting mantle, the models were set up in pairs of one including all thermal and compositional contributions to buoyancy (TC) and one accounting only for the thermal contributions (T). Single large impacts were introduced as causes of additional strong local anomalies, and their evolution in the framework of the convecting mantle was tracked. They confirm that the additional buoyancy provided by the depletion of melting mantle can establish a global stable stratification of the convecting mantle and throttle crust production. Furthermore, it is essential in the stabilization and preservation of local compositional anomalies directly beneath the lithosphere and offers a possible explanation for the existence of distinct, long-lived reservoirs in the martian mantle. Such anomalies will be detected by gravimetry rather than by seismic or heat flow measurements. The crustal thickness can be locally overestimated by up to 15-22 km if impact-induced density anomalies in the mantle are neglected.