Some comments on the rheologically critical melt percentage

The concept of rheologically critical melt percentage (RCMP) originally proposed by Arzi [Tectonophysics 44 (1978) 173–184] for partially molten granitic rocks is re-examined. It is shown that there is no experimental support to show the presence of RCMP. The published experimental data suggest that the effective viscosity of partially molten granitic rocks is reduced rapidly and continuously with increasing melt fraction. It is also shown that the experimental data may be modeled by means of the upper bound behavior (the Voigt bound) of two-phase material by assuming a melt localization, which implies that there is no partitioning of strain between the solid and the melt.