Effect of pressure on the strength of olivine at room temperature

• We synthesized fully dense polycrystalline olivine by spark plasma sintering.
• An olivine aggregate was deformed at room temperature and between 3 and 7 GPa.
• We determined a low-T plasticity flow law incorporating a pressure dependence.
• The pressure dependence of the Peierls stress is larger than expected.
• A viscosity of 1023 Pa.s is predicted for cold subducting slabs at 100 km depth.

A fine grained fully-dense olivine aggregate was deformed in a D-DIA press at room temperature and pressures ranging from 3.5 to 6.8 GPa, at constant strain rates between 6×10-66×10-6 and 2.2×10-52.2×10-5 s−1. A weighted non-linear least square fit of a dataset including our results and data from other high-pressure studies to a low-temperature plasticity flow law yields a Peierls stress σP0=7.4(0.5) GPa and an activation energy E∗=232(60) kJ.mol−1. The dependence of the Peierls stress to pressure, σP=σP0(1+0.09P), appears to be larger than the value predicted by the formulation proposed by Frost and Ashby (1982). With such a dependence, the activation volume is very small (V*=1.6(1.7) cm3.mol−1). Extrapolation to natural conditions yields a viscosity of ~1023-1024~1023-1024 Pa.s for a cold subducting slab at depths of 50–100 km.