Ductile vs. Brittle Strain Localization Induced by the Olivine–Ringwoodite Transformation

As it descends into the Earth’s mantle, olivine that constitutes lithosphere of subducting slabs transforms to its high-pressure polymorphs, wadsleyite and ringwoodite, in so-called transition zone. These transformations have important rheological consequences, since they may induce weakening, strain localization, and, some cases, earthquakes. In this study, germanium (Ge-olivine) was used as an analogue material investigate rheology samples undergoing olivine–ringwoodite transformation. Ge-olivine adopts a ringwoodite structure at pressures ~14 GPa lower than silicate counterpart does, making transformation accessible with Griggs rig. Deformation experiments were carried out new-generation apparatus, where micro-seismicity recorded form acoustic emissions. A careful analysis obtained signal, combined extensive microstructure recovered samples, provided major insights interplay between deformation mechanisms. The results show significant reaction rates cause weakening via implementation ductile shear zones can be preceded by small brittle precursors. When kinetics are more sluggish, mechanical instabilities lead transformational faulting, which stems from unstable propagation bands localizing both growth these is self-sustained thanks negative volume change exothermic nature reaction, leads dynamic rupture, attested emissions recorded. micro-earthquakes share striking similarities deep focus earthquakes, explain several seismological observations such magnitude frequency relations occurrence repeating earthquakes foreshocks.