Solution-precipitation enhanced creep in solid-liquid aggregates which display a non-zero dihedral angle

Experimental results and a corresponding model for solution-precipitation enhanced diffusional creep in solid-liquid aggregates which display a dihedral angle in the range 0° < θ ≤ 60° are presented. Partially molten assemblages with a crystalline residuum of olivine, (Mg, Fe)₂ SiO₄, deform at rates which are a factor of 2-5 faster than olivine without the liquid phase. Measured values of the activation energy suggest that, while the kinetics of deformation are enhanced by short-circuit diffusion through melt-filled triple junctions, the deformation behavior is rate-limited by matter transport through melt-free grain boundaries. The experimental results for steady-state deformation can be described by a geometric model whose primary variables are the dihedral angle and the volumetric melt fraction. Even though the rheology is Newtonian, a substantial deformation transient occurs during flow of a dense solid-liquid aggregate. Flexural creep experiments on a β-spodumene glass-ceramic demonstrate that this transient is a fully recoverable, anelastic flow which is caused by migration of the liquid phase, driven by the gradient in effective hydrostatic pressure across the specimen.