The Effect of Secondary-Phase Fraction on the Deformation of Olivine plus Ferropericlase Aggregates: 1. Microstructural Evolution

To study the microstructural evolution of polymineralic rocks, we performed deformation experiments on two-phase aggregates of olivine (Ol) + ferropericlase (Per) with periclase fractions (f(Per)) 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 ? = 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= f(Per)=0.5 and for those with 0.8= f(Per) =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.