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

The compositional diversity of the crust of Mercury revealed by NASAs 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 (1450-1750C; 5, 3.5, and 1.5 GPa) of potential primordial S-free and S-saturated mantlesand 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)containsunder above conditions. Our experimental data reveal thatthe majority of chemical composition of the highest Mg/Si region(HMR)on the Mercurys surface can result from ~2515 wt.% melting of a deepprimitive mantle. Additionally, the possibility that garnet was abundant in the deep mantle could explain that Mercury rocksbut the High-Mg province overlap the terrestrial Al-undepleted array, consistent with low-pressure melting of a garnet-free mantle.