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.

This study re-evaluates the adiabatic temperature profile of the Earth’s mantle. The global average temperature at the 410-km discontinuity is estimated to be 1805(18) K by comparing the globally averaged depths of the 410-km discontinuity with the previously determined phase diagram of the olivine-wadsleyite transition in the system (Mg,Fe)2SiO4 at two temperatures. The temperature at the 410-km discontinuity is extrapolated to shallower and deeper regions using the adiabatic temperature gradient, which is estimated from the pressure-volume-temperature relations and heat capacities of the major mantle minerals, namely, olivine, wadselyite, ringwoodite, and bridgmanite. The experimental temperatures and pressures in the original studies used in these evaluations are re-calculated using the recently proposed pressure correction on EMF of the W97Re3-W75Re25 thermocouple. The uncertainties are evaluated by the Monte Carlo simulation. The temperatures on the adiabatic geotherm are found to be 1617(16), 1959(19), 1925(19), and 2530(30) K, respectively, at a 50-km depth, just above the 660-km discontinuity, just below the 660-km discontinuity, and a 2800-km depth. These temperatures are higher than those given by Katsura et al. [2010]. The 50-km depth temperature is slightly higher but generally agrees to that estimated from the melting of depleted peridotite.

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 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 cross-slip controlled olivine dislocation creep.