Experimental constraints on the dynamics of the partially molten upper mantle: deformation in the diffusion creep regime

Deformation experiments have been conducted to investigate the effect of melt fraction and grain size on the creep behavior of olivine aggregates in the diffusion creep regime. Both nominally melt-free and melt-added samples display stress exponents and grain size exponents indicative of grain boundary diffusion creep. The activation energy for creep of the nominally melt-free aggregates is 315 ± 35 kJ/mol. An abrupt change in the rheological behavior of the partially molten aggregates occurs at a melt fraction of 0.05. A comparison with published diffusion data indicates that deformation is limited by transport of Si along melt-free grain boundaries under both melt-free and melt-present conditions. There is no difference in the strength of partially molten aggregates deformed with or without added water. -from Authors