Constraining melt concentration and strain distribution around basalt dykes in partially molten systems

Abstract

We performed experiments to determine melt concentration and strain distributions around basalt dykes in a San Carlos olivine matrix containing 10 wt% MORB. Undrained triaxial compression tests were conducted at 1473 K and confining pressure of 300MPa, at constant stresses (80-160 MPa) and constant strain rates ranging from 5x10-5s-1 to 3x10-4s-1, respectively. Melt distribution in the dyke/matrix interface was determined by image analysis and chemical profiles. Melt migration appears to be enhanced by porosity of the microstructure and by the loading conditions. The presence of the dyke does not influence the bulk strength of the sample. Highest melt concentrations, and presumably, the highest stress concentrations, are found at the tip of the dyke. The matrix deformation appears to be controlled by granular flow, but dilatancy occurs near the tip of the dyke, indicating coupled MORB transport and granular flow.