169 / 2023-04-15 01:40:23

Melting deep Mercury’s mantle constrained by high pressure-temperature experiments

高压物理与材料科学 > 高压地球科学-海报

The compositional diversity of volcanic rocks revealed by NASA’s MESSENGER at the surface of Mercury has been interpreted to result from partial melting of a heterogenous sulfur-rich Mercurian mantle. However, melting relations and the composition of partial melts for iron-free and sodium-rich mantle, together with the effect of sulfur as a key volatile, have not yet been studied in detail. In this study we present results from high-pressure and high-temperature experiments on the mineralogical and geochemical evolution of the mantle residue and melting products of primitive deep Mercury’s mantle with two starting compositions differing by their Mg/Si ratios. Both compositions have sulfur added as FeS. Experiments were conducted using a multi-anvil press under reduced conditions (by controlling the Si/SiO₂ ratio of the starting composition) at pressures of 3 and 5 GPa.

The residual mantle of Mercury with the lower Mg/Si ratio of 1.02 contains olivine + orthopyroxene above ~15 wt% melting at 3 and 5 GPa, and olivine disappears at melting over ~30 wt.% at 5 GPa. The Mercurian mantle with the Mg/Si of 1.35 contains olivine + orthopyroxene in the residue above ~15 wt% melting at 3 and 5 GPa, and olivine only when the melting degree is over ~50 wt.%. Our experiments also show that the majority of chemical composition of the High-Magnesium region (HMR) can result from ~25±15 wt.% melting of a deep primitive mantle. Further work will enable us to evaluate the compositional diversity of the mantle that is needed to explain the broad range of surface lavas.