RHEOLOGY OF PARTIALLY MOLTEN MANTLE ROCKS

▪ Abstract Over the past decade, significant progress has been made in understanding the rheological properties of partially molten mantle rocks. Laboratory experiments demonstrate that a few percent of melt can have an unexpectedly large effect on viscosity both in the diffusional creep regime and in the dislocation creep regime. In both cases, the enhancement in creep rate is much larger than anticipated based on deformation models because melt wets at least a fraction of the grain boundaries. For diffusion creep, the wetted interfaces provide a rapid diffusion path that is not included in analyses based on melt distribution in isotropic melt-crystal systems. For dislocation creep, two points require consideration. First, even without a melt phase present, fine-grained samples deformed in the dislocation creep field flow a factor of ∼10 faster than coarse-grained rocks due to contributions from grain boundary mechanisms to the deformation process. Second, melt has only a small effect on creep rate for c...

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