Effect of water on the rheology of iron rich olivine

We have undertaken an experimental investigation of the effect of water on the viscosity of iron rich olivine aggregates. Tri-axial compressive creep experiments were performed on hydrous fine-grained olivine samples of Fo₅₀, Fo₇₀, and Fo₉₀. Two drops of water were added for hot-pressing using a telescoping can to prevent the water from escaping during the hot-press. Samples were deformed in a gas-medium apparatus at a confining pressure of 300MPa, a temperature between 1323 and 1473K, a differential stress 10 ∼ 300MPa, a strain rate 10^-7 ∼ 10^-4s^-1, and the maximum accumulative strain 20% for each sample. The samples were deformed both in the diffusion and the dislocation creep regime. From three dimensional global non-linear fitting of the test data, the stress exponent for wet iron rich olivine aggregates Fo₅₀, Fo₇₀, and Fo₉₀,were determined as 3.8, 3.7 and 3.6 in dislocation creep regime, respectively, and the activation energy for wet Fo₅₀, Fo₇₀, and Fo₉₀, as 444kJ/mol, 479kJ/mol and 514kJ/mol, respectively. These hydrous samples creep at a rate over a factor of 10 faster than those anhydrous samples with the same iron content and under the same deformation conditions. Therefore, this paper gives a preliminary test result of effect of water on the viscosity of iron rich olivine aggregates.