Preferred Orientation Evolution of Olivine Grains as an Indicator of Change in the Deformation Mechanism

Abstract

The paper presents the results of investigations of deformed natural polycrystalline olivine. The relationship of the structure of polycrystalline olivine grains to three modal size distributions has been revealed. Grains of different size were observed to be strained at threshold temperatures of 950, 775, and 650°С. It has been demonstrated that the microstructure develops as the dislocation mechanism changes from diffusion creep to grain boundary sliding. The changes in deformation mechanisms promote the change in the preferred crystallographic orientations of olivine from type A to type D and then to type B. The relation of the transitions between different types of orientations to the conditions of deformation in the lower layers of the lithosphere at the plate boundaries is discussed.