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Dislocation creep of fine-grained olivine

# Dislocation creep of fine-grained olivine,10.1029/2009JB007174,Journal of Geophysical Research,U. H. Faul,J. D. Fitz Gerald,R. J. M. Farla,R. Ahlefeld

Dislocation creep of fine-grained olivine
Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing olivine show a stress dependence of the strain rate at stresses above ∼150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with $\dot {\epsilon }$$\propto$σn with n ∼ 7–8, or equally well by a Peierls creep law with exponential stress dependence. Due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse-grained polycrystals with n ∼ 3.5. TEM observations indicate the presence of dislocations with at least two different Burgers vectors, with free dislocations predominantly of screw character. Subgrain walls are present but are only weakly developed and have small misorientation angles. Both the rheology and dislocation structures are consistent with creep rate-limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size. Deformation mechanism maps extrapolated to lithospheric temperatures using the melt-free diffusion creep rheology of Faul and Jackson (2007), the dislocation creep rheology of Hirth and Kohlstedt (2003), and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of Peierls, dislocation, and diffusion creep.
Journal: Journal of Geophysical Research , vol. 116, no. B1, 2011
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## Citation Context (1)

• ...Much recent work has focussed on the use of pure polycrystalline iron-bearing olivine, (Mg,Fe)2SiO4, synthesized from laboratory reagents (Jackson et al. 2002; McDonnell et al. 2002; Faul and Jackson 2007)...
• ...Fully synthetic dry iron-bearing (Fo90) olivine has been prepared via a solution–gelation (sol–gel) method detailed in studies by (Jackson et al. 2002; Faul and Jackson 2007)...
• ...12% orthopyroxene (opx) as silica buffer and\1% porosity (specimen #6532 of Faul and Jackson 2007)...

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