Deformation of olivine in torsion under hydrous conditions

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

“…This layer acts as an imperfect mechanical boundary between the convecting mantle and the lithospheric plates. The maximum stresses obtained by our samples at 1000 °C surpass predictions from existing flow laws for this temperature domain (exponential law), but are indeed significantly lower than prediction deduced from high temperature flow laws (power law), without the intervention of additional weakening mechanism such as water weakening (e.g., Mackwell et al, 1985;Demouchy et al, 2012) or partial melting (e.g., Kohlstedt & Zimmerman, 1996). In consequence, the strength of olivine-rich rocks deformed at a temperature of 1000 °C and below, are in the order of 0.5 to 1 GPa when extrapolated at the strain rate of the mantle (e.g.…”

“…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).…”

“…Hirth & Kohlstedt (1996), Mei & Kohlstedt (2000 a,b), Demouchy et al (2012Demouchy et al ( , 2014, Fei et al (2013), Girard et al (2013) and Tielke et al (2017) confirm a weakening effect by water, although the most recent results highlight that it might induce a relatively limited effect (i.e., viscosity diminution by only a factor of 10 for hydrous olivine viscosity at mantle strain rates, Tielke et al, 2017) for hydrogen concentrations reported in spinel-bearing peridotite typical of the lithospheric mantle (Demouchy and Bolfan-Casanova, 2016). Based on high pressure deformation experiments, Karato and co-workers have proposed a classification in five types of olivine fabrics developing as a function of the applied stress and water content (Jung and Karato, 2001), but until now, the physical mechanism which could explain the crystallographic preferred orientations (CPO) variations is still lacking.…”

Modeling the effect of subgrain rotation recrystallization on the evolution of olivine crystal preferred orientations in simple shear

“…This characteristic evolution is well documented in simple shear experiments on olivine polycrystals at high temperature and moderate pressure conditions (Zhang and Karato, 1995;Bystricky et al, 2000;Demouchy et al, 2012;Hansen et al, 2014). It also corroborated by the analysis of the olivine CPO in shear zones in peridotite massifs (e.g., Warren et al, 2008) and by the limited range of CPO intensities in naturally deformed peridotites (Ben Ismaïl and Mainprice, 1998;Tommasi et al, 2000).…”

Characterization of the glide planes of the [001] screw dislocations in olivine using electron tomography

“…1 cm 3 (the starting ni sleeve is 9.45 mm in diameter and 20.03 mm long). The details of the geometry of the experimental set-up can be found in previous studies (Paterson 1990;Chen et al 2006;Demouchy 2010;Demouchy et al 2012Demouchy et al , 2013a. at high temperature, to buffer oxygen fugacity to values relevant of the upper most mantle (McCammon 2005), a pure nickel film has been integrated between the polycrystal olivine and the outer iron jacket.…”