Dislocation creep of fine-grained olivine

Abstract

[1] 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 _ / s n 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.

The stress dependence of olivine creep rate: Implications for extrapolation of lab data and interpretation of recrystallized grain size

“…(3) are ∼ 5 orders of magnitude smaller than observed, based on values for D Si vol from Dohmen et al (2002). Recent diffusion experiments on Fe-free olivine (Fei et al, 2012) yield diffusivities that are approximately two orders of magnitude greater than those determined by Dohmen et al (2002) at similar conditions. There are numerous ways to acquire apparently rapid diffusion rates (e.g., surface damage, impurities, short-circuit diffusion).…”

Elasticity of single-crystal olivine at high pressures and temperatures

“…However, previous deformation experiments, which provide crucial constraints on the LPO and slip systems of olivine, have been rarely performed at transition zone pressures (e.g. Demouchy et al, 2009;Durham et al, 1977;Faul et al, 2011;Hilairet et al, 2012;Jung and Karato, 2001;Katayama et al, 2004). Even the low pressure and high temperature experiments yield conflicting results (e.g.…”

“…Olivine transforms into wadsleyite at approximately 410-km depth and to ringwoodite at around 520-km depth, whereas pyroxene and garnet transform into majorite in the upper mantle and transition zone (Fei and Bertka, 1999). In our modeling, we have taken into account the phase relations as a function of depth as well as the partitioning of Fe between olivine polymorphs and between olivine and residual basaltic components at the phase equilibria using previous experimental and theoretical results (Akaogi et al, 1989;Angel et al, 1992;Irifune, 1987;Irifune and Isshiki, 1998;Irifune and Ringwood, 1987;Katsura and Ito, 1989;Pacalo and Gasparik, 1990;Stixrude and Lithgow-Bertelloni, 2005;Xu et al, 2008).…”

Stress evolution and associated microstructure during transient creep of olivine at 1000–1200 °C

“…The dominant deformation mechanism depends on the stress, temperature, grain size, strain rate, the crystal chemistry, the oxygen fugacity, partial melt content and even the trace amount of hydrogen (e.g. Carter & Lallemand, 1970;Chopra & Paterson, 1981Mackwell et al, 1985;Cooper & Kohlstedt, 1984, 1986Bai et al, 1991;Bai & Kohlstedt, 1992;Mei & Kohlstedt, 2000 a,b;Hirth & Kohlstedt, 1995, 2003Warren & Hirth, 2006;Mackwell, 2008;Faul et al, 2011Faul et al, , 2016Keefner et al, 2011;Demouchy et al, 2012;Tielke et al, 2016Tielke et al, , 2017. Dislocation glide is thought to be the dominant deformation mechanism at low temperatures (< 1200 °C in Fo 90 ) and for grain sizes > 1 mm prevalent in mantle olivine, since Si is the slowest diffusing species in silicates and its diffusivity is highly dependent on temperature (Chakraborty, 2010).…”

“…Chopra & Paterson, 1984;Karato et al, 1986;Bai et al, 1991;Hirth & Kohlstedt, 1995;Mei & Kohlstedt, 2000a, 2000bFaul et al 2011;Keefner et al, 2011;Tielke et al, 2017) to avoid to reach the brittle field. Experiments performed at temperatures relevant to the uppermost lithospheric mantle (≤ 1000 °C, e.g.…”