Olivine Deformation: To B Slip or Not to B Slip, That Is the Question

When deformed by dislocation creep the dominant slip (Burgers) vectors of olivine dislocations are parallel to [100] or [001]. Dislocations with an [010] Burgers vector component (b dislocations) have been recorded rarely. Here we show an experimentally deformed olivine sample has a substantial population (17%) of b dislocations. Electron Backscatter Diffraction maps of crystal orientations provided information on dislocations from the orientation gradients. Maps show the b dislocations form subgrain walls like those formed by other dislocation types and are interpreted to form similarly by glide and climb, so b dislocations are mobile. To confirm our approach, we used Electron Backscatter Diffraction maps to select an area for Transmission Electron Microscopy imaging, down to an atomic scale image of a b dislocation. Our sample was deformed within range of subduction zone conditions; our approach can be used to investigate the scale and conditions of b slip in the mantle more widely.