Effects of water on dynamically recrystallized grain-size of olivine

Recrystallized grain-size versus stress relationship for olivine has been determined under water-poor and water-rich conditions. We found that when the water content in olivine exceeds ∼800 ppm H/Si, the size of recrystallized grains is about two to three times larger than under water-poor conditions, compared at the same stress level. Microstructural observations of deformed samples show that the ratio of recrystallized grain size to that of subgrains increases significantly with water content and that the volume fraction of grains containing subgrain-boundaries is smaller under water-rich conditions than under water-poor conditions. These observations suggest that the enhancement of grain-boundary mobility by water is more significant than that of dislocation recovery, leading to a larger size of recrystallized grains under water-rich conditions.