Thermo-Rheological Structure of the Martian Lithosphere: Effects of Mantle's Iron Content

Meteorite, cosmochemical, and geophysical data collectively suggest that the Martian mantle is enriched in iron by a factor of 2–3 compared to Earth's mantle. However, the impact of the high iron content on the thermo-rheological structure and evolution of the Martian lithosphere remains unclear. Here, we combine the latest constraints from the InSight mission and experimental results to quantitatively assess the effect of mantle iron content on the Martian lithosphere. The results show that an increase in iron content from ${\text{Fa}}_{10}$ to ${\text{Fa}}_{30}$ leads to a temperature increase of 200–300 K at a depth of 200 km. This high iron content also weakens Mars' lithosphere and yields a decrease in ∼30 km on average in effective elastic thickness and ∼70 km in thermal lithospheric thickness. The iron-weakening effect thins the transition layer between the lithosphere and convective mantle and enlarges their viscosity contrast to four orders of magnitude. We speculate that high iron content promotes decoupling of the lithosphere from the deep mantle and causes Mars to stay in a stagnant lid regime. Our work indicates that future Martian lithosphere studies should consider the iron-weakening effect.