The Effect of Secondary‐Phase Fraction on the Deformation of Olivine + Ferropericlase Aggregates

Harison S Wiesman, Mark E Zimmerman, David L Kohlstedt

OAI: oai:www.repository.cam.ac.uk:1810/348720 • DOI: 10.17863/CAM.96146

To study the microstructural evolution of polymineralic rocks, we performed deformation experiments on two‐phase aggregates of olivine (Ol) + ferropericlase (Per) with periclase fractions (fPer) between 0.1 and 0.8. Additionally, single‐phase samples of both Ol and Per were deformed under the same experimental conditions to facilitate comparison of the microstructures in two‐phase and single‐phase materials. Each sample was deformed in torsion at T = 1523 K, P = 300 MPa at a constant strain rate up to a final shear strain of γ = 6 to 7. Microstructural developments, analyzed via electron backscatter diffraction (EBSD), indicate differences in both grain size and crystalline texture between single‐ and two‐phase samples. During deformation, grain size approximately doubled in our single‐phase samples of Ol and Per but remained unchanged or decreased in two‐phase samples. Zener‐pinning relationships fit to the mean grain sizes in each phase for samples with 0.1 ≤ fPer ≤ 0.5 and for those with 0.8 ≥ fPer ≥ 0.5 demonstrate that the grain size of the primary phase is controlled by phase‐boundary pinning. Crystallographic preferred orientations, determined for both phases from EBSD data, are significantly weaker in the two‐phase materials than in the single‐phase materials.

Chemistry and Physics of Minerals and Rocks/Volcanology geochemistry Subduction zone processes MARINE GEOLOGY AND GEOPHYSICS MINERALOGY AND PETROLOGY MINERAL PHYSICS Creep and deformation X‐ray neutron and electron spectroscopy and diffraction PHYSICAL PROPERTIES OF ROCKS MICROSTRUCTURE plasticity diffusion and creep TECTONOPHYSICS Volcanology RESEARCH ARTICLE olivine periclase torsional deformation MICROSTRUCTURE EBSD Zener pinning