Wetting of enstatite by basaltic melt at 1350°C and 1.0‐ to 2.5‐Gpa Pressure

Abstract

The results of partial melting experiments of olivine, enstatite, and basalt PG‐16A at 1350°C and pressures from 1.0 to 2.5 GPa indicate that the melt wets enstatite with a dihedral angle of 20°–40° in the presence of small amounts of H2O. This angle is significantly less than the critical dihedral angle of 60°, and thus the melt can distribute itself in an interconnected network of prismatic channels along the grain edges, where enstatite is the dominant solid phase. The dihedral angles from olivine‐enstatite‐melt triple junctions are such that an interconnected network of melt channels is also possible where enstatite and olivine occur in similar proportions. Together with the results of previous partial melting experiments in the olivine‐basalt systems, the results of this study suggest that in the Earth's upper mantle the melt will occur largely in networks of interconnected channels along the intergranular edges, where morphologies are controlled by thermodynamic equilibrium. We conclude that the presence of enstatite will have no significant effect on the permeability of partially molten zones in the mantle, if small amounts of H2O are present.