Melt Stability and Compaction in a Partially Molten Silicate Layer Heated from Below
In this paper, the possibility of convective or Rayleigh-Taylor instability in a growing layer of partially molten material, heated from below, is investigated. The relative importance of matrix compaction and thermal conduction on the dynamics of the partially molten layer is also studied by a scaling analysis of the appropriate dimensionless equations. The analysis shows that, for low viscosity melts, thermal conduction is unimportant; and melt dynamics is controlled by a combination of matrix compaction and buoyantly-driven instabilities within the melt itself. Once these instabilities occur, melt migration becomes a two- or three-dimensional process, and the chemical composition of the melt that leaves the source zone represents a mixture of melts produced at different temperature-pressure regimes in the source area. In melts with high viscosity, thermal conduction dominates the thermal regimes. Compaction and shear deformation of the matrix must both act to segregate the melt from the matrix. The melt is stable with respect to thermal or compositional convection until a large quantity of liquid has coalesced.
KeywordsRayleigh Number Bulk Composition Source Zone Local Thermodynamic Equilibrium Compositional Gradient
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