Deformation and texture development in deep Earth mineral phases: Implications for seismic anisotropy and dynamics.

摘要

The contribution of this thesis is to expand the current knowledge of deformation mechanisms in mineral phases of the lower mantle, the D" region, and the inner core. Quantitative information about texture and stress is obtained using in-situ radial synchrotron x-ray diffraction and the Rietveld method to deconvolute diffraction images. Transformation textures are interpreted in terms of structural relationships between the starting material and product phases or in terms of minimization of strain energy. Polycrystal plasticity modeling is used to interpret deformation textures in terms of activity of slip systems and mechanical twinning.;In Chapter 2 texture development resulting from phase transformations and deformation is explored in (Mg,Fe)SiO3 perovskite and (Mg,Fe)SiO 3 perovskite + (Mg,Fe)O magnesiowiistite aggregates in the diamond anvil cell (DAC). For (Mg,Fe)SiO3 perovskite synthesized from enstatite a strong 001 texture develops that is related to a structural relationship between the enstatite and perovskite phases. For (Mg,Fe)SiO3 perovskite + (Mg,Fe)O magnesiowiistite aggregates synthesized from (Mg,Fe)2SiO 4 olivine and ringwoodite, transformation textures are controlled by minimization of strain energy during the phase transformation via mechanical twinning and/or nucleation of grains in low strain energy configurations. Polycrystal plasticity modeling of deformation textures indicates that slip on (001) planes dominates in (Mg,Fe)SiO3 perovskite at high pressure and room temperature and this does not appear to change with laser heating. Interestingly when two phase aggregates of (Mg,Fe)SiO3 perovskite + (Mg,Fe)O magnesiowtistite are deformed, magnesiowustite does not develop significant texturing, which may indicate that it would not be a source of anisotropy in the lower mantle.;Deformation of CaIrO3 post-perovskite (an analog for (Mg,Fe)SiO 3 postperovskite) in the deformation-DIA large volume press is explored in chapter 3. A sintered polycrystalline sample of CaIrO3 post-perovskite is deformed at a variety of pressure and temperature conditions up to 6 GPa and 1300 K and at a varying strain rates. In all cases (010) lattice planes align perpendicular to the compression direction upon shortening, and there is little change in texture with temperature, pressure, or strain rate Polycrystal plasticity modeling shows that this texture pattern is consistent with slip on (010)[100]. This is in contrast to textures produced in room-temperature diamond anvil cell (DAC) measurements on MgGeO3 and MgSiO 3 pPv which display textures with (100) and (110) lattice planes at high angles to the compression direction. Thus it is likely that CaIrO3 post-perovskite is not a good analog for the plastic behavior of MgSiO3 pPv.;Chapter 4 explores transformation and deformation textures in bcc, fcc, and hcp phases of Fe deformed in a laser heated DAC. Specifically radial DAC techniques have been advanced by developing a method to simultaneously heat and perform controlled deformation using a gas membrane driven DAC system and in-situ laser heating. In bee iron, room temperature compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the deformation induced phase transformation to hcp iron, a subset of orientations preferentially transform to the hcp structure first generating a texture of (011¯0) planes at high angles to compression. With further deformation, remaining grains transform, and this results in a texture that obeys the Burgers relationship of (110) bcc//(0001)hcp. This is in contrast to high temperature results that indicate that texture is developed through dominant pyramidal ⟨a+c⟩ {211 2}(2113) and basal (0001)(2 110) slip. The high temperature fcc phase develops a 110 texture typical for fcc metals deformed in compression. (Abstract shortened by UMI.)