Climb of jogs as a rate-limiting process of screw dislocations motion in
olivine dislocation creep
Abstract
Dislocation recovery experiments were conducted on pre-deformed olivine
single crystals at temperatures of 1,450 to 1,760 K, room pressure, and
oxygen partial pressures near the Ni-NiO buffer to determine the
annihilation rates constants for [001] (010) edge dislocations. The
obtained rate constants were comparable with those of previously
determined [001] screw dislocations. The activation energies for the
motion of both dislocations are identical. This suggests that the motion
of screw dislocations in olivine is not controlled by cross-slip but by
the same rate-limiting process of the motion of edge dislocations, i.e.
climb, at low-stress and high-temperature conditions. The diffusivity
derived from dislocation climb indicates that dislocation recovery is
controlled by pipe diffusion. The conventional climb controlled model
for olivine can be applied to the motions of not only edge but also
screw dislocations. The softness of the asthenosphere cannot be
explained by the cross-slip controlled olivine dislocation creep.