The effect of crystal orientation on the wetting behaviour of silicate melts on the surfaces of spinel peridotite minerals

The effect of crystal anisotropy on wetting angles of equilibrium silicate melts on crystal faces of spinel, diopside, enstatite and olivine has been determined experimentally by the sessile melt drop technique. The anisotropy, Ãγ_SL, of solid-liquid interfacial energies (γ_SL(max)-γ_SL(min)) can be related to the wetting angles, ψ, by Ãγ_SL ∝ /cos ψ (max) - cos ψ (min)/ = Pw_(-maA_7SL) Normalising to the smallest wetting angle gives values of Pw for diopside = 0.0728, olivine = 0.0574, orthopyroxene =0.0152, and spinel = 0.0075. Crystal anisotropy influences grain-scale morphology of small-degree partial melts, permeability and the melt connectivity threshold, ∅_C. Results show that, at sufficient melt fractions, diopside should increase permeability in a peridotitic matrix, whereas enstatite should lower it. Despite its low anisotropy, spinel contributes positively to permeability and ∅_C because of its high surface energies. These results suggest that harzburgitic mineral matrices typical of the subcratonic mantle should impede the movement of low-degree partial melts, whereas melts should flow more easily through spinel lherzolites.