Effect of melt squeezing rate on shear stress along a simulated fault in gabbro during frictional melting

Abstract

High-velocity friction experiments were performed on gabbro at an initial constant slip rate of 1.32 m/s and normal stress of 1.2 MPa. Under these conditions, the sliding surfaces melted due to frictional heating. Once steady-state conditions (shear strength and shortening rate of the sample) in the presence of melt were achieved, normal stress was increased gradually up to 4.5 MPa to simulate enhanced squeezing of melt from the slipping zone. At low normal stress, shear stress increased only slightly with increasing normal stress. When normal stress increased above 2.5 MPa, however, shear stress showed a linear increase with increasing normal stress. We propose that the deformation mechanism changes from melt-separated viscous shear to a mixed lubrication (solid-solid contact + frictional melting) due to a reduction in the thickness of the melt layer associated with an increase in the melt squeezing rate at high normal stresses. Copyright 2007 by the American Geophysical Union.