SIMULATING SHEAR- INDUCED MELT BANDS BELOW MID-OCEAN RIDGES

The large volume of oceanic crust and the narrow region of mid-ocean ridge volcanism require efficient lateral transport of melt beneath mid-ocean ridges. One proposed mechanism for lateral transport of melt involves the formation of bands of high porosity and permeability that result from shear flows in the mantle caused by large-scale mantle convection. Bands of high and low porosity have been seen in the laboratory in cm scale deformation experiments and porosity bands have been simulated numerically for a number of idealized flow geometries. The orientation of bands depends on the orientation at which they grow, which depends on the geometry of the flow field and the rheology of the solid matrix. The orientation of the bands also depends on the rotation of the bands by the background flow. The ability of the porosity bands to act as rapid conduits for melt depends on their orientation relative to the mid-ocean ridge. In this work, we present calculations based on linearized and nonlinear solutions of the compaction equations for the orientations and amplitudes of melt bands in a sub-mid-ocean ridge –like corner flow. The orientations and amplitudes of the bands are calculated for fast and slow spreading ridges and for various matrix rheologies. We find that for porosity-only dependent matrix viscosity, melt bands are not well oriented to channel melt towards mid-ocean ridges but may be well oriented to channel melt to sub-lithospheric decompaction layers.