Effect of iron content on the creep behavior of olivine: 1. Anhydrous conditions

High-temperature, high-pressure triaxial compressive creep experiments were carried out on polycrystalline samples of olivine, (Fe_xMg_{1 - x})₂SiO₄, with x ≡ Fe/(Fe + Mg) = 1.0, 0.75, 0.5, and 0.3 to investigate the influence of Fe content on rheological properties of olivine under anhydrous conditions. Samples with grain sizes of < 50 μm were deformed at differential stresses of 50 to 300 MPa primarily in the dislocation-accommodated grain boundary sliding creep regime for temperatures between 1273 and 1473 K with a confining pressure of 300 MPa. Our results, combined with published results on aggregates of Fa₁₀, demonstrate that samples of Fa₃₀, Fa₅₀, Fa₇₅, and Fa₁₀₀ creep ~ 15, ~ 75, ~ 365, and ~ 1480 times faster than samples of Fa₁₀, respectively, under the same conditions. Our experimental results can be described by the flow lawover(ε, ̇) = over(ε, ̇)_gbs⁰ (frac(σ, μ))^ngbs (frac(b, d))² X_Fa^p exp (- frac(Q_gbs^o + α X_Fa, R T)) with over(ε, ̇)_gbs⁰ = (6.2 ± 5.2) × 10⁵ s^{- 1}, n_gbs = 3.9,p = 1.5 ± 0.1, Q_gbs⁰ = 440 ± 10 kJ/mol, and α = - 45 ± 4 kJ/mol. Based on measured dependence of strain rate on iron concentration, we conclude that, at the same thermodynamic conditions, the Martian mantle, which is more rich in Fe than Earth's mantle, will be a factor of ~ 10 less viscous than Earth's mantle.