Experimental deformation of muscovite shear zones at high temperatures under hydrothermal conditions and the strength of phyllosilicate-bearing faults in nature

Layers of fine-grained muscovite were hot-pressed then sheared between alumina sliders to shear strains up to 2, at temperatures between 300 and 700 °C, confining pressures of 206 MPa and various pore water pressures. High pore water pressures helped suppress dehydroxylation of the mica and permitted testing at temperatures higher than previously used. Shear strain rates between 10-3 s-1 and 10-7 s-1 were accessed using constant shear strain rate and stress relaxation testing. Except for strain rates