Stress-driven melt segregation in partially molten olivine-rich rocks deformed in torsion

Torsion experiments on partially molten aggregates of olivine + chromite + 4 vol. % mid-ocean ridge basalt provide new insights into the interactions between deformation and melt segregation. When samples are sheared, melt segregates into distinct melt-rich bands oriented ~20° antithetic to the macroscopic shear plane. In one series of experiments, samples were deformed at similar shear strain rates (or stresses) to a range of finite shear strains to explore the evolution of melt-rich bands. In another series of experiments, samples were deformed to similar finite shear strains at a range of strain rates to explore the effect of strain rate (or stress) on band spacing and microstructure. We relate variations in strain rate to the compaction length and show that band spacing increases with increasing compaction length.These experiments provide new information on the evolution of melt distribution, the partitioning and localization of strain, and the scaling of experimental results to the Earth's mantle.