Shearing Melt Out of the Earth: An Experimentalist's Perspective on the Influence of Deformation on Melt Extraction

Melt extraction from the Earth's mantle requires some form of channelized flow to produce the observed disequilibrium between the crust-forming lavas and their mantle sources. In this review, we discuss the influence of deformation on melt-extraction processes, with an emphasis on the understanding gained from a wide range of laboratory experimental investigations. Rheological properties of partially molten rocks are very sensitive to melt distribution, and melt distribution is profoundly influenced by deviatoric stress in a viscously deforming partially molten rock, establishing a coupling between deformation and melt distribution. During deformation, this coupling can lead to organization of melt into melt-enriched shear zones at length scales longer than the grain size. We discuss the current state of understanding of this process, with some speculation on its role in the ensemble of processes that constitute melt extraction from the Earth.