One of the principal means of understanding upper mantle dynamics involves inferring mantle flow directions from seismic anisotropy under the assumption that the seismic fast direction (olivine a axis) parallels the regional flow direction. We demonstrate that (i) the presence of melt weakens the alignment of a axes and (ii) when melt segregates and forms networks of weak shear zones, strain partitions between weak and strong zones, resulting in an alignment of a axes 90 degrees from the shear direction in three-dimensional deformation. This orientation of a axes provides a new means of interpreting mantle flow from seismic anisotropy in partially molten deforming regions of Earth.

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Results of microfocus X-ray diffraction at the ESRF are presented which provide unique evidence supporting a model for the structure of starch, much of this model having been previously derived only on the basis of circumstantial evidence. Here we present data from ∼2 μm regions within granules which have been subjected to no sample preparation and obtain oriented 2-D fiber patterns from the edge of B-type potato starch granules. This data is in good agreement with that previously calculated by Imberty/Perez for a B-type amylose fiber. The peripheral amylopectin helices are oriented in such a way they do not point to a single focus. No discontinuities (“grain boundaries”) within a granule could be found at the 10 μm level of resolution.

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It is shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fibers with a 2 μm synchrotron radiation beam in a few seconds per pattern. Preferred orientation was observed for an ultrahigh molecular weight polyethylene fiber where orthorhombic plus monoclinic phases were found to coexist in the outer parts of the fiber. For a poly(p-phenyleneterephthalamide) fiber (Kevlar 49) the radial sheet model was verified, but an important texture appears to be present.

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Synthesized polycrystalline enstatite samples were deformed in a Paterson gas‐medium apparatus at 1200–1300°C, oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 MPa (protoenstatite field) or 450 MPa (orthoenstatite field). At both confining pressures, the mechanical data display a progressive increase of the stress exponent from n = 1 to n~3 with increasing differential stress, suggesting a transition from diffusional to dislocation creep. Nonlinear least squares fits to the high‐stress data yielded dislocation creep flow laws with a stress exponent of 3 and activation energies of 600 and 720 kJ/mol for orthoenstatite and protoenstatite, respectively. Deformed samples were analyzed using optical microscopy and scanning and transmission electron microscopy. Microstructures show undulatory extinction and kink bands, evidence of dislocation processes. Crystallographic preferred orientations measured by electron backscatter diffraction are axisymmetric and indicate preferential slip on (100)[001]. Most deformed grains comprise an interlayering of orthoenstatite and clinoenstatite lamellae. While many lamellae may have formed during quenching from run conditions, those in samples deformed in the orthoenstatite field are often bordered by partial [001] dislocations, suggesting transformation due to glide of partial [001] dislocations in (100) planes. Comparison of our orthoenstatite creep law with those for dislocation creep of olivine indicates that orthoenstatite deforms about a factor of 2 slower than olivine at our experimental conditions. However, as orthoenstatite has a higher activation energy and smaller stress exponent than olivine, this strength difference is likely smaller at the higher temperatures and lower stresses expected in much of the upper mantle.