Diffusion creep of dry, melt‐free olivine

Abstract

[1] Deformation experiments were conducted on fine-grained (3-6 mm), fully synthetic Fo 90 olivine aggregates in a gas-medium apparatus at 300 MPa confining pressure and temperatures of 1150-1360°C. The strain rates of the solution-gelation-derived and therefore genuinely melt-free, dry samples are about two orders of magnitude lower than the strain rates for nominally melt-free aggregates at the same pressure and temperature conditions and grain size. Benchmark deformation tests with Anita Bay dunite and mild steel reproduce published data. The creep strength of melt-added sol-gel olivine is similar to the published creep strength of dry, melt-bearing olivine derived from natural rocks. Nonlinear least-squares fits to the melt-free deformation data give an activation energy of 484 kJ/mol, a stress exponent of 1.4, and a grainsize exponent of 3 over a range of stresses from 15 to 210 MPa. These results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water. However, a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments.

(An)elastic softening from static grain boundaries and possible effects on seismic wave propagation

“…This brings the behaviour close to diffusion assisted grain boundary sliding and, for sufficiently long timescales, to steady state diffusional creep. Experimentally, such behaviour was observed in olivine by Faul and Jackson (2007) (see also Yoshino et al 2007;Schmeling 1985). The interfacial shear modulus in the transform domain can now replace the static interfacial modulus so that the structure of the solutions shows the typical viscous decay of the shear modulus from the initial, elastic limit to the final limit which can equally be understood as an elastic limit where all inclusions are replaced by voids.…”

Slip-system and EBSD analysis on compressively deformed fine-grained polycrystalline olivine

“…Sol-gel olivine material was prepared from dissolution of Fe and Mg nitrates in an ethanol solution (Jackson et al 2002;Faul & Jackson 2007). A second type of olivine material was prepared from crushed San Carlos phenocrysts (Tan et al 2001).…”

Water disequilibrium in olivines from Hawaiian peridotites: Recent metasomatism, H diffusion and magma ascent rates

“…Faul and Jackson, 2007;Demouchy et al, 2013) and Si diffusion in olivine (Kohlstedt, 2006;Costa and Chakraborty, 2008). It may be argued that temporary storage of H in the Mg-site may delay peridotite weakening and potential delamination along a water-bearing melt conduit, the latter only occurring after equilibration when most H occupies Si vacancy related defects.…”