Dislocation recovery experiment of hydrous olivine as a function of water content and crystallographic orientation
Final Report Abstract
The followings are main findings obtained by the present project. 1. Edge dislocations with a [100] Burgers vector are responsible for the [100](010) slip (Type A), which are called a‐dislocation here. 2. Screw dislocations with a [001] Burgers vector is responsible for both the [001](010) slip (Type B) and [001](100) slip (Type C), which are called c‐dislocation here. 3. There are no dislocations responsible for the [100](001) slip (Type E). The a‐dislocations are activated by this slip. 4. Magnitudes of annihilation rate constants of a‐ and c‐dislocations are comparable within 0.3 orders of magnitude. 5. Pressure and temperature dependence of annihilation rate constants of a‐ and c‐dislocations are identical. 6. The water‐content exponent of a‐dislocations is 0.2 0.4, which is much smaller than expected from the deformation experiments but identical to those from Si diffusion experiments within the uncertainties. 7. The water‐content exponent of c‐dislocations is 0.5 0.2, which is much smaller than expected from the deformation experiments but identical to those from Si diffusion experiments within the uncertainties. 8. Thus, the effects of water on the dislocation mobility are very small. 9. Although the results of the deformation experiment imply the water content dependence of mobility of the c‐dislocation should be larger than that of the a‐dislocations, it is comparable or even smaller. 10. The fabric transitions from Type A to Type E and then to Type C suggested by the deformation experiments are unlikely in the mantle. These results will fundamentally change our understanding about the relations between water incorporation and dislocation creep and the origin of variation of seismic anisotropy. However, we need some more efforts to increase the quality of the data about the water‐content dependence of dislocation annihilation‐rate constants and to examine kinds and properties of dislocations accounting for the reported olivine fabrics.
Publications
- (2016), Temperature dependence of [100](010) and [001](010) dislocation mobility in natural olivine, Earth Planet. Sci. Lett., 441, 81‐90
Wang, L., S. Blaha, Z. Pintér, R. Farla, T. Kawazoe, N. Miyajima, K. Michibayashi, and T. Katsura
(See online at https://doi.org/10.1016/j.epsl.2016.02.029)
