Experimental constraints on the strength of the lithospheric mantle

To provide a better understanding of rheological properties of mantle rocks under lithospheric conditions, we carried out a series of experiments on the creep behavior of polycrystalline olivine at high pressures (∼4-9 GPa), relatively low temperatures (673 ≤ T ≤ 1273 K), and anhydrous conditions, using a deformation-DIA. Differential stress and sample displacement were monitored in situ using synchrotron X-ray diffraction and radiography, respectively. Experimental results were fit to the low-temperature plasticity flow law, ε̇ = A_Pσ²exp[-E _k(0)/RT(1 - √σ/σ_P)]. On the basis of this analysis, the low-temperature plasticity of olivine deformed under anhydrous conditions is well constrained by our data with a Peierls stress of σ_P = 5.9 0.2 GPa, a zero-stress activation energy of E _k(0) = 320 50 kJ mol^-1, and A_P = 1.4 × 10^-7 s^-1 MPa^-2. Compared with published results for high-temperature creep of olivine, a transition from low-temperature plasticity to high-temperature creep occurs at ∼1300 K for a strain rate of ∼10^-5 s^-1. For a geological strain rate of 10 ^-14 s^-1, extrapolation of our low-temperature flow law to 873 K, the cutoff temperature for earthquakes in the mantle, yields a strength of ∼600 MPa. The low-temperature, high-stress flow law for olivine in this study provides a solid basis for modeling tectonic processes occurring within Earth's lithosphere.