Plastic deformation of polycrystalline MgO up to 1250 K and 65 GPa

Understanding the development of lattice preferred orientations (LPO) in polycrystals is critical to constrain the anisotropy and dynamics of the Earth mantle. Until recently, it was not possible to study LPO under high pressure and high temperature. The introduction of the deformation-DIA (D-DIA) and radial diffraction experiments in the diamond anvil cell (DAC) have extended the range of pressures and temperatures that can be accessed. However, the pressure range accessible in the D-DIA remains limited (up to 19 GPa, 1) and LPO measurements in the DAC have been performed at 300 K (2). Recently, we have designed a new DAC that can be used to study LPO in polycrystalline samples up to temperatures of 1300 K and pressures of 65 GPa (3). In this study, we use this new device for the study of MgO up to 65 GPa and 1250 K. Four samples of polycrystalline MgO were deformed in the DAC at constant temperature: 300, 600, 900, and 1250 K. At each temperature, we study the development of stress and LPO as the sample is compressed between ambient and high pressures (up to 65 GPa). In all cases, we collect diffraction data in a radial geometry that can be used to extract lattice strains and LPO in the sample. A comparison of the LPO measured in the experiment and results of visco-plastic self-consistent models can be used to extract information about the active deformation mechanisms in the sample (2). Similarly, the measured lattice strains can be compared to results of an elasto-plastic self-consistent model to extract information on average stress, stress distribution among grains, and active deformation in the sample (4). Details of the measurements along with the LPO measured in the experiments will be presented. We will also discuss the implication of those results for our understanding of the behavior of MgO in the deep mantle. 1- N. Nishiyama, Y. Wang, M. L. Rivers, S. R. Sutton, D. Cookson, Rheology of e-iron up to 19 GPa and 600 K in the D-DIA, Geophys. Res. Lett., 34, L23304 (2007) 2- S. Merkel, H.-R. Wenk, J. Shu, G. Shen, P. Gillet, H.-K. Mao, R. J. Hemley, Deformation of polycrystalline MgO at pressures of the lower mantle J. Geophys. Res., 107, 2271 (2002) 3- H.-P. Liermann, S. Merkel, L. Miyagi, H.-R. Wenk, G. Shen, H. Cynn, W.J. Evans, New Experimental Method for In Situ Determination of Material Textures at Simultaneous High-Pressure and Temperature by Means of Radial Diffraction in the Diamond Anvil Cell, Review of Scientific Instruments, in press 4- S. Merkel, C.N. Tomé, H.-R. Wenk, A modeling analysis of the influence of plasticity on high pressure deformation of hcp-Co Phys. Rev. B, 79, 064110, 2009