High-pressure and high-temperature deformation experiments on polycrystalline wadsleyite using the rotational Drickamer apparatus

Abstract

High-pressure, torsional deformation experiments on polycrystalline wadsleyite were carried out using the rotational Drickamer apparatus (RDA). The experimental conditions ranged between temperatures of ~2000–2200 K at pressures of ~20 ± 1 GPa. Prior to deformation, the fine-grained (1–5 µm) wadsleyite specimens were synthesized from San Carlos olivine in a Kawai-type multi-anvil apparatus. The samples were loaded in the RDA, pressurized and heated, and deformed at stepped strain rates of 5–60 × 10−6 s−1. The stress was determined through the analysis of the orientation dependence on changes in lattice spacing for the (141), (240) and (040) planes. The strain was determined from the orientation of a molybdenum strain marker. Most stepped strain-rate tests reveal the stress exponent n to be 4.7 ± 0.5, suggesting power-law dislocation creep operated. Various samples exhibit grain-size reduction (to 0.1–0.6 µm), possibly associated with dynamic recrystallization or with partial phase transformation to ringwoodite. Transmission electron microscopy and electron backscatter diffraction analyses provide information on the dominant slip system in wadsleyite as 1/2〈111〉 slip on {101} planes, as well as slip in the [100] direction. Dislocation density, even in recrystallized grains, is very high (likely >1014 m−2), reflecting the final high stresses in the samples during deformation. The results provide greater constraints on the regimes of various deformation mechanisms in wadsleyite at various experimental conditions.