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

Abstract

The 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 0.0–2.5 wt% dissolved Cl, at 0.7, 1.1, and 1.5 GPa. 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.