The olivine-spinel transformation in the Earth's mantle is believed to have an important effect on the dynamics of subduction. It is possible that under P-T conditions of subducting slabs the transformation is kinetically inhibited. The possible metastable persistance of olivine to depths far below 400 km (which is a critical requirement in current models of deep-focus earthquakes) will be tested by determining the transformation kinetics experimentally .
Samples of mantle olivine are partially reacted at various P-T conditions (e.g. 18 GPa, 10000C) using a multianvil press. The microstructures of partially-reacted samples are characterised using optical and transmission electron microscopy. The time-dependence of the microtextures enables rates of nucleation and growth to be estimated as a function of P and T. Using appropriate kinetic rate equations, combined with thermal models, the experimental data will be used to quantify the depth of the olivine-spinel transformation in subduction zones.