Mass transfer processes in crystalline aggregates containing a fluid phase

Understanding mass transfer processes in porous crystalline aggregates containing a fluid phase is of major importance for modelling partially molten regions of the Earth's mantle, such as those under mid-ocean spreading ridges. Despite the fact that mid-ocean ridges can be considered the simplest large scale setting where partial melting occurs, many processes at depth beneath the ridges, such as segregation and migration ofthe melt phase, remain poorly understood. For example, essential input information for large scale modelling, such as the melt distribution on the grain scale, whether or not a continuous network of (grain-scale) melt channels exists and the associated transport properties, are poorly constrained. Also poorly constrained is the effect of melt on the rheological behaviour of mantle rock. When trying to combine information from equilibrium (hydrostatic) melt distribution studies and densification or deformation studies on partially molten samples, the difficulty arises that little or no information is available under conditions where both stress-related and surface-energy-related driving forces for grain scale diffusive mass transfer are comparable in magnitude. Such conditions may, however, be important in partially molten regions of the earth. This thesis reports a theoretical and experimental study of grain scale mass transfer processes in solid/fluid systems under the low effective stress conditions where surface energy related forces are expected to become significant.