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.
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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