Creep behavior of Fe‐bearing olivine under hydrous conditions. Issue 9 (11th September 2015) - Tasaka, Miki
Abstract: To understand the effect of iron content on the creep behavior of olivine, (Mg x Fe(1 − x ) )2 SiO4, 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 ˙ = ε ˙ 0.90 1 − x 0.1 1 / 2 exp 226 × 10 3 0.9 − x R T . In this equation, the strain rate of San Carlos olivine, ε ˙ 0.90, is a function of T, σ, and f H 2 O . 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. Key Points: Deformation experiments on polycrystalline olivine under hydrous conditions The first experiments using various iron contents of polycrystalline wet olivine Viscosity of the iron‐rich mantle of Mars can be estimated using the flow law