Melting the mantle of Mercury and the compositional diversity of the crust

The compositional diversity of the crust of Mercury revealed by NASA’s MESSENGER spacecraft is interpreted to result from partial melting of a heterogeneous sulfur-rich Mercurian mantle. Major magmatic activity and the building of its secondary volcanic crust are restricted to the first billion year of the planet evolution. In order to understand the causes for the production of diverse lavas and the early death of major volcanism, we have performed a suite of high-pressure and high-temperature partial melting experiments under reduced conditions at temperature and pressure conditions relevant the mantle (1450-1750°C; 5, 3.5, and 1.5 GPa) of potential primordial S-free and S-saturated mantles and obtained crystallization sequences, solidus and liquidus of the residual mantle of Mercury with the Mg/Si ratio of 1.02 (Mer8) and 1.35 (Mer15) contains under above conditions. Our experimental data reveal that the majority of chemical composition of the highest Mg/Si region (HMR) on the Mercury’s surface can result from ~25±15 wt.% melting of a deep primitive mantle. Additionally, the possibility that garnet was abundant in the deep mantle could explain that Mercury rocks but the High-Mg province overlap the terrestrial “Al-undepleted” array, consistent with low-pressure melting of a garnet-free mantle.