Terra Nova, 24, 62–69, 2012
Experiments comprising deformation at 600 °C and annealing at 700–1000 °C were performed on natural peridotite to examine the microfabric evolution at conditions corresponding to those prevailing just below the seismogenic zone in suboceanic upper mantle. The found olivine microstructures indicate that deformation occurs by low-temperature plasticity. At low and high annealing temperatures, zones of high strain are replaced by subgrains and recrystallized grains respectively. The microstructures after annealing at 1000 °C resemble ‘core-and-mantle structures’ from shear zone peridotites, often interpreted as imprint of steady-state dislocation creep. Our study shows that such structures can form by a sequence of low-temperature plasticity at high stress and subsequent recrystallization at low stress, as corresponding to coseismic deformation and post-seismic creep. In this case, palaeopiezometers are not applicable and a local CPO in aggregates of new grains does not necessarily indicate the activated glide system.