Identical activation volumes of dislocation mobility in the [100](010) and [001](010) slip systems in natural olivine

Abstract

Dislocation recovery experiments were performed on predeformed olivine single crystals at pressures of 2, 7 and 12 GPa and a constant temperature of 1650 K to determine the pressure dependence of the annihilation rate constants for [100](010) edge dislocation (a dislocation) and [001](010) screw dislocation (c dislocation). The constants of both types of dislocations are comparable within 0.3 orders of magnitude. The activation volumes of a and c dislocations are small and identical within error: 2.7 ± 0.2 and 2.5 ± 0.9 cm3/mol, respectively. These values are slightly larger and smaller than those of Si lattice and grain‐boundary diffusions in olivine, respectively. The small and identical activation volumes for the a and c dislocations suggest that the pressure‐induced fabric transition is unlikely in the asthenosphere. The decrease in seismic anisotropy with depth down in the asthenosphere may be caused by the fabric transition from A type or B type to AG type with decreasing stress with depth.

Ultra-high pressure inclusion in Archean ophiolitic podiform chromitite in mélange block suggests deep subduction on early Earth

“…Outcrop-scale structures show high-temperature deformation in schlieren and chromitemylonites, whereas microstructural studies of the Zunhua chromites (Li et al, 2002;Huang et al, 2004;Polat et al, 2006;Kusky et al, 2007) documented high-temperature grain boundary pullaparts, preferred crystallographic slip on (010) [100] slip systems in olivine inclusions, asymmetric recrystallized tails on orthopyroxene porphyroclasts, high-temperature deformation bands in inclusions in olivine, and used established paleothermometers (Holtzman, 2000;Nicolas, 1989;Nicolas and Azri, 1991), to estimate the crystallization temperatures of the chromite to have been between 1000 °C and 1250°C, consistent with recent high-pressure experimental work (Raterron et a., 2012;Wang et al, 2017;Wallis et al, 2019). Age constraints on the formation of the mélange, the blocks contained therein, and of the chromite grains are described in detail in W.B.…”

Subgrain Rotation Recrystallization During Shearing: Insights From Full‐Field Numerical Simulations of Halite Polycrystals

“…Therefore, the approach taken is the most appropriate for estimating M 0 values. A comparison of the kinetics of recovery calculated from annealing experiments (Borthwick and Piazolo, 2010;Farla et al, 2010;Wang et al, 2017) versus those using our approach is discussed in the supporting information and Figure S1.…”