Experimental constraints on the strength of the lithospheric mantle

Abstract

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, . 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 σP = 5.9 ± 0.2 GPa, a zero‐stress activation energy of Ek(0) = 320 ± 50 kJ mol−1, and AP = 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.