Complications to Carbonate Melt Mobility due to the Presence of an Immiscible Silicate Melt

Abstract

The relative interfacial energies of immiscible carbonate and silicate number of incompatible elements, and can be very mobile. Their mobility is a result of their low viscosities melts were investigated in olivine and clinopyroxene matrices. Carbonate melt has a higher melt–solid interfacial energy than does the [0·01–0·1 Pa s at temperatures >500°C, for a range of compositions (Dawson et al., 1990; Wolff, 1994; Dobson coexisting silicate melt. The silicate melt therefore selectively wets the grain-edge channels between solid phases, excluding the carbonate et al., 1996)] and their ability to form an interconnected grain-edge melt at low melt fractions. Dunitic assemblages melt to the center of melt pockets, away from grain edges. This prevents the carbonate melt from migrating independently of the (and probably other mineralogies) with an interconnected carbonate melt should have a high permeability to flow. silicate melt and the carbonate melt is unable to separate from the silicate melt in a solid-dominated assemblage. The carbonate melt These melts may transport a variety of trace elements and can infiltrate long distances into the country rock will migrate effectively only after the silicate melt has solidified, or by separating from the silicate melt within liquid-dominated reservoirs surrounding melt channels, altering the chemistry and isotopic systems of the host rock. Diffusion is fast within (sills, dikes, or chambers), unrestricted by solid interfaces. This relative wetting behavior may help explain the close association of these melts, so even a stagnant interconnected melt can greatly enhance the transport of trace and major elements carbonate and silicate magmas in alkali complexes, and their relative timing of emplacement. These results also place constraints on the (Watson, 1991). generation and separation of derivative melts in carbonated silicate The relative interfacial energy between grain–grain melt systems and on the style and timing of alkali wall-rock contacts and grain–fluid contacts can be parameterized metasomatism. by the dihedral angle, the angle subtended at a fluid– grain–grain junction. Dihedral angles >60° indicate that system interfacial energy is minimized by reducing the contact of the fluid with the solid, whereas systems with dihedral angles <60° minimize interfacial energy by