Olivine-Spinel Transition Olivine-Spinel Transition 
Olivine-spinel structural transition are the possible cause for the deep earthquakes occur at depth of 400-700 km, along the Earth's subducting lithosphere. The earthquakes frequency shows a continuous distribution with minimum at 400km, peaking around 500-600 km and diminishing at 700 km. The fact that the earthquakes occurs at such a range of depth implies some mechanism is controlling the kinetics of the phase transition and triggering it at certain condition. Our goal was to subject the olivine to severe deformation in a non-hydrostatic diamond-anvil cell and see whether it affect the kinetics of the phase transition.
Fe2SiO4, Mg2SiO4, Co2SiO4, Ni2SiO4, and Mg2GeO4 in the olivine structure are found to transform to the spinel structure in a non-hydrostatic DAC at temperatures 100-200 C lower than in previous studies in which conditions were more hydrostatic. The distribution of the spine-structure phases within the sample can be explained by the distribution of deviatoric stresses and the evolution of plastic flow in a non-hydrostatic DAC.
The spinel phase, which in many of the samples is distributed in an annular pattern, exhibits reconstructive textures including grain boundary nucleation, and lack of topotaxy; in some cases it forms lenses similar to those associated with transformation-induced mechanical failure. Although spinel phase lamellae, formed by a martensiticlike mechanism, are observed in the specimens, the lamellae remain extremely thin (~10 nm) and do not produce enough spinel to be optically visible. The observation of reconstructive textures within the annular transformed regions leads us to conclude that high shear stress and plastic strain enables reconstructive transformation at temperatures where transformation rates would otherwise be virtually zero. High transient differential stresses and rapid deformation accompany deep earthquakes. Therefore knowledge of the kinetics of this transformation under these conditions is important for understanding the connection between Spinel ring in Mg2GeO4 Spinel ring in Fe2SiO4 with central amorphous phase Spinel ring in Ni2SiO4
