Climb of jogs as a rate-limiting process of screw dislocations motion in
olivine dislocation creep
Abstract
Dislocation recovery experiments were conducted on predeformed 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 rate constants for [001](010) edge dislocations. The
obtained rate constants were found to be comparable to those of
previously determined [001] screw dislocations. The activation
energies for the motion of both dislocations are identical. This result
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, under low-stress,
high-temperature conditions. The diffusivity derived from dislocation
climb indicates that dislocation recovery is controlled by Si pipe
diffusion, rather than Si lattice diffusion. Our results suggest that
the conventional climb-controlled model for olivine can be applied to
motions of not only edge but also screw dislocations. Therefore, the
previous proposed cross-slip model cannot explain the softness of
asthenosphere.