High-temperature viscoelasticity of fine-grained polycrystalline olivine |
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Authors: | B H Tan I Jackson J D Fitz Gerald |
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Institution: | Research School of Earth Sciences, Australian National University, Canberra 0200 ACT, Australia?e-mail: Ian.Jackson@anu.edu.au, AU
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Abstract: | Torsional forced-oscillation and microcreep methods have been employed in a study of the viscoelastic behaviour of fine-grained
polycrystalline olivine at high temperatures (to 1300 °C), seismic frequencies and low strain amplitudes. The Fo90 specimens are of low porosity and low dislocation density. They vary in mean grain size from 8 to 150 μm and contain only
trace amounts (≪0.1 vol%) of quenched melt glass. For T ≤ 900 °C, their behaviour is essentially elastic and the shear modulus G closely approaches that expected for a dense polycrystal from single-crystal elasticity data – confirming the suppression
of thermal microcracking in␣this study. At higher temperatures, pronounced absorption-band dissipation and associated dispersion␣of
the shear modulus provide evidence of linear viscoelastic behaviour. Both recoverable (anelastic) and permanent (viscous)
strains are involved and the proportion of the latter increases with increasing temperature and decreasing frequency. Comparison
of the results for the three specimens provides a clear indication that the viscoelastic behaviour, attributed to diffusional
processes, is grain-size-sensitive with the dissipation and associated dispersion increasing with decreasing grain size. Both
elastically accommodated and diffusionally accommodated grain-boundary sliding appear to be implicated.
Received: 29 September 2000 / Accepted: 7 May 2001 |
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Keywords: | Olivine Viscoelastic behaviour Andrade model Burgers model Seismic wave attenuation Anelastic behaviour Grain boundary Diffusion |
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