Grain misorientations in partially molten olivine aggregates: an electron backscatter diffraction study |
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Authors: | Ulrich H Faul John D Fitz Gerald |
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Institution: | (1) Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia e-mail: uli.faul@anu.edu.au Fax: +61-2-6249-3414, AU |
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Abstract: | In polycrystalline aggregates of olivine with mean grain sizes above 35 μm plus a low basaltic melt fraction, both wetted
and melt-free grain boundaries are observed after equilibration times at high pressures and temperatures of between 15 and
25 days. In order to assess a possible dependence of the wetting behaviour on the relative orientation of neighbouring grains,
a SEM based technique, electron backscatter diffraction (EBSD), is used to determine grain orientations. From the grain orientations
relative orientations of neighbouring grains are calculated, which are expressed as misorientation axis/angle pairs. The distribution
of misorientation angles and axes of melt-free grain boundaries differ significantly from a purely random distribution, whereas
those of wetted grain boundaries are statistically indistinguishable from the random distribution. The relative orientation
of two neighbouring grains therefore influences the character of their common grain boundary. However, no clustering towards
special (coincident site lattice) misorientation axes is observed, with the inference that the energy differences between
special and general misorientations are too small to lead to the development of preferred misorientations during grain growth.
Received: 8 December 1997 / Revised, accepted: 6 April 1998 |
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Keywords: | Partial melt Grain boundary Olivine Misorientation Electron backscatter diffraction |
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