Theories for deformation of polycrystals have been substantially refined, enabling us to model deformation of metals and minerals with considerable sophistication. So far, most modelling has been confined to single‐phase aggregates such as quartzite and limestone. We present the first results for a polyphase aggregate, peridotite, consisting of 70% olivine and 30% enstatite. The problem is approached with a viscoplastic self‐consistent theory satisfying stress equilibrium and strain compatibility for the average polycrystal and taking account of anisotropic neighbor interactions. It is assumed that olivine deforms by (010)[100], (001)[100], and (010)[001] slip and enstatite deforms by (100)[001] slip. Simulated textures for olivine and enstatite in peridotite resemble simulated textures in the pure phases, indicating that for this system and for these volume fractions there is little influence of the different phases upon each other. In our model the harder mineral enstatite deforms at a slower rate than olivine. Interaction between neighboring grains appears to be minimal, which may be due to model assumptions. Predicted pole figures with olivine (010) axes and enstatite (100) axes aligning with the direction of shortening are in good agreement with preferred orientations in naturally and experimentally deformed peridotites.

On the basis of polycrystalline theory describing the plasticity in olivine and enstatite, the flow in a convection cell has been simulated using a finite element formulation. The spatial variations in anisotropic properties are computed from the textures that evolve with the flow. A kinematically constrained equilibrium‐based assumption is used to partition the macroscopic deformation among crystals within an aggregate. We model the convection for one specific cell geometry and two sets of boundary conditions. A complete map of textures throughout the cell is obtained. The textured convection cell is structurally very heterogeneous and textures along streamlines do not correlate with the finite strain. The results of the simulations indicate that during up welling a strong texture develops rapidly. It convects during spreading and is attenuated during subduction. Results are compared with features of the upper mantle. In our predictions the pattern of preferred orientation during spreading is inclined to the flow coordinates due to deformation by simple shear. This is contrary to Hess' [1964] intuition that (001) slip planes of olivine orient themselves parallel to the flow planes, yet the pattern is consistent with natural fabric data. Significant differences are observed as a function of depth within the cell. The variations in the p wave velocities in this textured model mantle are analyzed and correspond well with observed seismic data.

This article documents a new in situ deformation apparatus built for neutron diffraction investigations of polycrystalline materials in low-temperature environments and the first experiment in which it was used. We performed texture analysis of fine-grained polycrystalline D2O ice Ih deformed uniaxially between 230 and 240K using time-of-flight neutron diffraction on the high-pressure preferred orientation diffractometer at the Manuel Lujan, Jr. Neutron Scattering Center at Los Alamos National Laboratory. The new deformation apparatus operates at 1atm of ambient pressure and over temperatures in the range of 77K<T<298K, and accommodates up to 667N of uniaxially applied load. It is suitable for diffraction studies of any bulk polycrystalline material, ideally cylindrical in shape, and is adaptable to multiple neutron spectrometers, including those at other polychromatic and monochromatic neutron facilities. The first experiment on a hexagonal ice sample demonstrates development of fiber texture in the direction of the applied load. The equipment has many applications to earth science, glaciology, and ice engineering.

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