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

Abstract

High-temperature, high-pressure triaxial compressive creep experiments were carried out on polycrystalline samples of olivine, (Fe x Mg 1 − x ) 2SiO 4, 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 Fa 10, demonstrate that samples of Fa 30, Fa 50, Fa 75, and Fa 100 creep ~ 15, ~ 75, ~ 365, and ~ 1480 times faster than samples of Fa 10, respectively, under the same conditions. Our experimental results can be described by the flow law ε ˙ = ε ˙ gbs 0 ( σ μ ) n gbs ( b d ) 2 X Fa p exp ( - Q gbs o + α X Fa R T ) with ε ˙ gbs 0 = ( 6.2 ± 5.2 ) × 10 5 s - 1 , n gbs = 3.9 , p = 1.5 ± 0.1, Q gbs 0 = 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.