Elastic softening of peridotite due to the presence of melt phases at high pressure

Here we report an observation of softening of Young's modulus of a sample of KLB-1 peridotite as a metallic Ni melt intruded into it at 2.5 GPa and about 1500 °C. A uniaxial oscillation of stress was applied to the sample with frequency of 0.01-0.02 Hz and an amplitude up to 500 MPa. The Young's modulus is measured as the amplitude ratio between the sample and a reference material, while the attenuation is determined by the phase angle delays. The Ni intrusion was captured by in situ X-ray radiography. A planar intrusion occurred gradually, but advanced only during the extension; eventually, the Ni melt dissected the sample on a plane normal to the extension axis. Accompanied softening of Young's modulus was observed after the Ni intrusion was completed. This study suggests that percolation of a liquid metallic phase is possible within a partially melted mantle rock in the presence of a differential stress field.