Dislocation interactions during low-temperature plasticity of olivine and their impact on the evolution of lithospheric strength

Dislocation interactions in olivine control postseismic creep of the upper mantle

“…Therefore, although it is difficult to calculate the effective back stress from observed stress heterogeneity and vice versa, the mechanical data 31 and microstructural observations (Figs. 1, 2, and 4-6) 37,38 , are consistent in indicating the role of long-range dislocation interactions in generating kinematic strain hardening. Long-range internal stresses have been interpreted to play a key role in establishing steady-state creep by dislocationaccommodated grain boundary sliding, which was inferred by Hansen et al 23 to be the dominant deformation mechanism in the aggregates deformed at high temperatures that we investigated.…”

“…Strainhardening transients are exhibited by single crystals of olivine deforming by both low-temperature plasticity [30][31][32] and powerlaw creep at high temperatures 9,33,34 , with the transition between mechanisms occurring at temperatures of~1000-1100°C at typical experimental stresses and strain rates. Microstructural analyses of single crystals deformed in both temperature regimes indicate that strain hardening results from increases in dislocation density 9,[35][36][37] , short-range dislocation interactions 33 , and long-range interactions among dislocations via their stress fields 37,38 . Short-range interactions involve local rearrangement of atoms in the vicinity of adjacent dislocation cores.…”

What Controls Effective Elastic Thickness of the Lithosphere in the Pacific Ocean?

“…Laboratory experiments indicate that grain size reduction (Kumamoto et al., 2017) and increasing plastic strain (Hansen et al., 2019) lead to significant hardening of olivine at low temperature. At subduction zones, large bending‐related stresses in the lower part of the plate may create abundant dislocations with low mobility and large plastic strain, leading to high yield strength (Hansen et al., 2019; Wallis et al., 2020). Therefore, when flexed by long‐wavelength and high‐amplitude loads, the plate stiffens and does not readjust to smaller loads, resulting in low compensation and therefore high inferred .…”

“…Strain hardening only occurs at low temperature, large plastic strain (up to 2%), and small grain size, and is limited by the onset of diffusion‐based, steady‐state creep mechanisms at higher temperature (Hansen et al., 2019; Wallis et al., 2020). Such hardening is therefore not expected to operate where very young and hot lithosphere is subducting, for example, in southern Chile, Central America and the Cascadia subduction zone, where temperature (and therefore steady‐state creep) effects dominate.…”

“…Finally, although this model remains speculative, hardening mechanisms remain to be rigorously incorporated and tested in yield strength envelope modeling of (see Hansen et al., 2019; Wallis et al., 2020). In addition to the effect of temperature on yield strength, the amount of plastic strain (which can be calculated from observed plate curvature) could be considered when interpreting results over oceanic domains.…”