Abstract
Various dihedral angles were measured in partially molten, synthetic peridotite (Fo60 En35 Ab2.5 (wt%)), pressure‐annealed at 1.5 GPa (15 kbar), 1400°C (water free) for 192 hours and 1250°C (water saturated) for 212 hours; the melt fractions in the two specimens were 8.2% and 9.2%, respectively. The orthopyroxene‐melt interface shows the greatest difference in dihedral angles between the water‐free and saturated samples. At textural equilibrium the melt phase exists stably at grain edges except at those edges which include two or three orthopyroxene grains in the water‐free specimen. The melt phase is stable in all corners for both the water‐free and saturated samples. The equilibrium melt phase distribution for a system of two solids with coexisting melt is characterized by a newly proposed stability criteria. We conclude that the network of melt phase through edges and corners becomes more connected in the water saturated partial melt. It is suggested that the connectivity of the melt phase through grain edges is likely to be interrupted by the presence of orthopyroxene grains in dry ultramafic rocks. The increase of the melt fraction and/or the water content in the melt tends to diminish this “pyroxene effect.”
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