Creep behavior of Fe-bearing olivine under hydrous conditions

To understand the effect of iron content on the creep behavior of olivine, (Mg_xFe_(1-x))₂SiO₄, under hydrous conditions, we have conducted tri-axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x=0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050° to 1200°C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas-medium high-pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53≤x≤0.90 in the dislocation creep regime: ε=ε0.901-x0.11/2exp226×1030.9-xRT. In this equation, the strain rate of San Carlos olivine, ε0.90, is a function of T, σ, and fH2O. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.