The influence of mantle melting on the evolution of Mars

We present a parameterized convection model of Mars by incorporating a new heat-flow scaling law for stagnant-lid convection, to better understand how the evolution of Mars may be affected by mantle melting. Melting in the mantle during convection leads to the formation of a compositionally buoyant lithosphere, which may also be intrinsically more viscous by dehydration. The consequences of these melting effects on the evolution of terrestrial planets have not been explored before. The temporal evolution of crust and lithospheric mantle is modeled in a self-consistent manner considering mantle melting, convective instability, and the rewetting of dehydrated lithosphere from below by hydrogen diffusion. Though the effect of compositional buoyancy turns out to be minimal, the introduction of viscosity contrast between wet and dry mantle can considerably slow mantle cooling and sometimes lead to non-monotonic core cooling. Furthermore, with or without dehydration stiffening, our model predicts that the martian mantle must have been degassed more extensively (>80%) than previously suggested (<10%); the loss of such a large amount of water from the mantle to surface has significant implications about the role of water in the early surface and climate evolution of Mars.