Justin Filiberto

High pressure, near‐liquidus phase equilibria of the Home Plate basalt Fastball and melting in the Martian mantle

Near-liquidus phase equilibria experiments have been conducted on a synthetic Fastball basalt composition, as analyzed at Home Plate plateau of Mars (Gusev Crater), to test if it represents a primitive mantle derived melt and place constraints on the temperature of the ancient mantle and on the lithosphere-asthenosphere boundary of Mars. The Fastball basalt is multiply saturated with olivine and orthopyroxene at ∼1.2 GPa and 1430°C. Based on melting models, we predict that the Fastball composition could be produced by 13–23% equilibrium melting of the Martian mantle, with extraction of melt from the base of ∼105 km thick lithosphere. The multiple saturation for Fastball also constrains the potential temperature of the Martian mantle to be approximately 1480–1530°C with an initial melting pressure of 4.0–4.7 GPa. This potential temperature is much lower than that of the terrestrial mantle derived from similarly ancient magmas, i.e., komatiites.

Effect of chlorine on near-liquidus phase equilibria of an Fe–Mg-rich tholeiitic basalt

AbstractnThe importance of Cl in basalt petrogenesis has been recognized, yet constraints on its effect on liquidus crystallization of basalts are scarce. In order to quantify the role of Cl in basaltic systems, we have experimentally determined near-liquidus phase relations of a synthetic Fe–Mg-rich basalt, doped with 0.0–2.5xa0wt% dissolved Cl, at 0.7, 1.1, and 1.5xa0GPa. Results have been parameterized and compared with previous data from literature. The effect of Cl on mineral chemistry and liquidus depression is dependent on the starting basaltic composition. The liquidus depression measured for a SiO2-rich, Al2O3-poor basalt is smaller than that observed for a basaltic melt depleted in silica and enriched in FeOT and Al2O3. The effect of Cl on depression of the olivine–orthopyroxene–liquid multiple saturation pressure does not seem to vary with the starting composition of the basaltic liquid. This suggests that Cl may significantly promote the generation of silica-poor, Fe–Al-rich magmas in the Earth, Mars, and the Moon.