Experimental constraints on the strength of the lithospheric mantle

[1] 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 (similar to 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, (epsilon) over dot = A(P)sigma(2) exp[-Ek(0)/RT (1-root sigma/sigma(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 sigma(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 x 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 similar to 1300 K for a strain rate of similar to 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 similar to 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.