On the relative importance of thermal and chemical buoyancy in regular and impact-induced melting in a Mars-like planet

TL;DR

This study uses numerical simulations to evaluate how thermal and chemical buoyancy influence mantle dynamics and melting processes in a Mars-like planet, highlighting the importance of compositional effects in mantle stratification and reservoir preservation.

Contribution

It demonstrates the critical role of compositional buoyancy in mantle stability, long-lived reservoirs, and impact effects, advancing understanding of Mars's interior evolution.

Findings

Compositional buoyancy stabilizes mantle and preserves anomalies.

Impact-induced density anomalies affect crustal thickness estimates.

Chemical buoyancy influences global mantle stratification.

Abstract

We ran several series of two-dimensional numerical mantle convection simulations representing in idealized form 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 and one accounting only for the thermal contributions. In several of the model pairs, single large impacts were introduced as causes of additional strong local anomalies, and their evolution in the framework of the convecting mantle was tracked. The models confirm that the additional buoyancy provided by the depletion of the mantle by regular melting can establish a global stable stratification of the convecting mantle and throttle crust production. Furthermore, the compositional buoyancy 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. The detection of such anomalies by geophysical means is probably difficult, however; they are expected to be detected by gravimetry rather than by seismic or heat flow measurements. The results further suggest that the crustal thickness can be locally overestimated by up to ~20 km if impact-induced density anomalies in the mantle are neglected.