Linear analysis of melt band formation in a mid-ocean ridge corner flow

Abstract

Imposing external shear on systems of partial melt can cause compaction of the solid matrix and concentration of the interstitial liquid melt thereby generating bands of contrasting high and low porosity. These shear-induced porosity bands have been proposed to channel melt beneath a mid-ocean ridge (MOR). In this contribution, we impose a shear flow that evolves as the bands are transported along streamlines of MOR corner flow. We evaluate the suitability of porosity band formation as a mechanism for melt channeling beneath a MOR using a linear instability analysis with three different matrix viscosity conditions: isotropic strain rate independent, isotropic strain rate dependent, and anisotropic. Our analysis shows that the largest amplitude bands channel melt away from the ridge axis toward the base of the plate at the lithosphere-asthenosphere boundary, while the effectiveness of channeling through the bands is highly dependent on the mantle bulk viscosity.