Plastic deformation of olivine at relatively low temperatures (i.e., low-temperature plasticity) likely controls the strength of the lithospheric mantle in a variety of geodynamic contexts. Unfortunately, laboratory estimates of the strength of olivine deforming by low-temperature plasticity vary considerably from study to study, limiting confidence in extrapolation to geological conditions. Here we present the results of deformation experiments on olivine single crystals and aggregates conducted in a deformation-DIA at confining pressures of 5 to 9 GPa and temperatures of 298 to 1473 K. These results demonstrate that, under conditions in which low-temperature plasticity is the dominant deformation mechanism, fine-grained samples are stronger at yield than coarse-grained samples, and the yield stress decreases with increasing temperature. All samples exhibited significant strain hardening until an approximately constant flow stress was reached. The magnitude of the increase in stress from the yield stress to the flow stress was independent of grain size and temperature. Cyclical loading experiments revealed a Bauschinger effect, wherein the initial yield strength is higher than the yield strength during subsequent cycles. Both strain hardening and the Bauschinger effect are interpreted to result from the development of back stresses associated with long-range dislocation interactions. We calibrated a constitutive model based on these observations, and extrapolation of the model to geological conditions predicts that the strength of the lithosphere at yield is low compared to previous experimental predictions but increases significantly with increasing strain. Our results resolve apparent discrepancies in recent observational estimates of the strength of the oceanic lithosphere.
Bibliographical noteFunding Information:
We are grateful for the efficient and excellent technical assistance of Haiyan Chen at beamline 6‐BM‐B at the Advanced Photon Source. We are also thankful for help with sample and assembly preparation from Rellie Goddard and fabrication of assembly parts by Kurt Leinenweber, Jamie Long, and James King. The manuscript was greatly improved by thoughtful reviews from Joerg Renner and Claudia Trepmann. This research was supported by Natural Environment Research Council grant NE/M000966/1 to L. N. H. and D. W.; Advanced Photon Source General User Proposal 55176 to L. N. H., D. L. K., D. L. G., and W. B. D.; National Science Foundation Award EAR‐1361319 to W. B. D. and EAR‐ 1806791 to K. M. K.; and the Department of Energy National Nuclear Security Administration Stewardship Science Graduate Fellowship to C. D. M. Use of the COMPRES Cell Assembly Project was supported by COMPRES under NSF Cooperative Agreement EAR 1661511. The data used are presented in the figures and tables.
©2019. The Authors.
- strain hardening