Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine

Kumamoto, Kathryn M.; Thom, Christopher A.; Wallis, David; Hansen, Louis S.; Armstrong, David E.J.; Warren, J. M.; Goldsby, D. L.; Wilkinson, Angus J.

doi:10.1126/sciadv.1701338

Cited by 63 publications

(148 citation statements)

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“…The model calibrated in the previous section has several major implications for the strength of the lithosphere. First, as initially suggested by Kumamoto et al (), the grain size dependence of yield strength in olivine suggests that the strength of the coarse‐grained upper mantle may be lower by a factor of 5 than previous predictions based on experiments on fine‐grained olivine aggregates. However, the high degree of strain hardening observed in our experiments implies that, although the lithosphere may be initially weak at yield, it will strengthen quickly with progressive deformation.…”

Section: Discussionmentioning

confidence: 98%

“…In Figure , we have compiled estimates of yield strength from previously published deformation experiments on olivine. Following Kumamoto et al (), we compare our results to previously published results as a function of the characteristic length scale of deformation, taken to be the grain size for experiments on polycrystals and the contact radius for indentation experiments. To compare data from our room‐temperature experiments to previous data from experiments at higher temperature, we have extrapolated previously published flow laws to room temperature and calculated the stress.…”

Section: Discussionmentioning

confidence: 99%

“…Since the total magnitude of hardening during the first loading cycle (i.e., flow stress minus yield stress) is on the order of the apparent back stress (Table ), it is reasonable to assume that the hardening observed in our experiments is dominated by kinematic, rather than isotropic, hardening. The importance of kinematic hardening in moderating the strength of olivine is also evidenced by the nanoindentation experiments of Kumamoto et al () that revealed significant accumulation of GNDs and residual stresses associated with low‐temperature plasticity.…”

Section: Discussionmentioning

confidence: 99%

“…This indentation‐size effect, well documented in the literature on engineering materials (for a review, see Pharr et al, ), is potentially linked to the Hall‐Petch effect, whereby yield stress increases with decreasing grain size of a material (Hou et al, ; Zhu et al, ). Kumamoto et al () hypothesized that the discrepancy among previous studies resulted primarily from comparing the results from experiments conducted on samples with different grain sizes, a conclusion supported by a compilation and reanalysis of published results taking account of grain size. On this basis, they predicted that olivine with the relatively large grain sizes characteristic of Earth's upper mantle has much lower strength than typically estimated from the results of experiments performed on finer‐grained materials.…”

Section: Introductionmentioning

confidence: 99%

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Low‐Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere

et al. 2019

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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.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low‐Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere

et al. 2019

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“…Zhong and Watts (2013) found that laboratory-derived LTP flow laws (e.g., Mei et al, 2010) must be weakened by a preexponential factor of 10 8 in order to reproduce the amplitude and wavelength of the observed flexure and depth distribution of seismicity at Hawaii. This has led to new experimental studies on the cause of the discrepancy between the field-based and laboratory studies on the LTP flow laws (Idrissi et al, 2016;Kumamoto et al, 2017). However, there are several limitations in the approach of Zhong and Watts (2013) that require further investigation.…”

Section: Introductionmentioning

confidence: 99%

Constraints on the Rheology of the Lithosphere From Flexure of the Pacific Plate at the Hawaiian Islands

Bellas

Zhong

Watts

2020

Geochem Geophys Geosyst

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The rheology of oceanic lithosphere is important to our understanding of mantle dynamics and to the emergence and manifestations of plate tectonics. Data from experimental rock mechanics suggest rheology is dominated by three different deformation mechanisms including frictional sliding, low‐temperature plasticity, and high‐temperature creep, from shallow depths at relatively cold temperatures to large depths at relatively high temperatures. However, low‐temperature plasticity is poorly understood. This study further constrains low‐temperature plasticity by comparing observations of flexure at the Hawaiian Islands to predictions from 3‐D viscoelastic loading models with a realistic lithospheric rheology of frictional sliding, low‐temperature plasticity, and high‐temperature creep. We find that previously untested flow laws significantly underpredict the amplitude and overpredict the wavelength of flexure at Hawaii. These flow laws can, however, reproduce observations if they are weakened by a modest reduction (25–40%) in the plastic activation energy. Lithospheric rheology is strongly temperature dependent, and so we explore uncertainties in the thermal structure with different conductive cooling models and convection simulations of plume‐lithosphere interactions. Convection simulations show that thermal erosion from a plume only perturbs the lithospheric temperature significantly at large depths so that when it is added to the thermal structure, it produces a small increase in deflection. In addition, defining the temperature profile by the cooling plate model produces only modest weakening relative to the cooling half‐space model. Therefore, variation of the thermal structure does not appear to be a viable means of bringing laboratory‐derived flow laws for low‐temperature plasticity into agreement with geophysical field observations and modeling.

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Dislocation creep of olivine: Backstress evolution controls transient creep at high temperatures

Hansen

Wallis

Breithaupt

et al. 2021

Preprint

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Transient creep occurs during geodynamic processes that impose stress changes on rocks at high temperatures. The transient is manifested as evolution in the viscosity of the rocks until steady-state flow is achieved. Although several phenomenological models of transient creep in rocks have been proposed, the dominant microphysical processes that control such behavior remain poorly constrained. To identify the intragranular processes that contribute to transient creep of olivine, we performed stress-reduction Preprint submitted to ESSOAr and Journal of Geophysical Research -Solid Earth 2 tests on single crystals of olivine at temperatures of 1250-1300°C. In these experiments, samples undergo time-dependent reverse strain after the stress reduction. The magnitude of reverse strain is ~10 -3 and increases with increasing magnitude of the stress reduction. High-angular resolution electron backscatter diffraction analyses of deformed material reveal lattice curvature and heterogeneous stresses associated with the dominant slip system. The mechanical and microstructural data are consistent with transient creep of the single crystals arising from accumulation and release of backstresses among dislocations. These results allow the dislocation-glide component of creep at high temperatures to be isolated, and we use these data to calibrate a flow law for olivine to describe the glide component of creep over a wide temperature range. We argue that this flow law can be used to estimate both transient creep and steadystate viscosities of olivine, with the transient evolution controlled by the evolution of the backstress. This model is able to predict variability in the style of transient (normal versus inverse) and the load-relaxation response observed in previous work.c Cooper et al. Hanson and Spetzler This study Normal Inverse

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Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine

Abstract: When deforming by low-temperature plasticity, the strength of the mantle mineral olivine is controlled by its grain size.

Cited by 63 publications

References 61 publications

Low‐Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere

Low‐Temperature Plasticity in Olivine: Grain Size, Strain Hardening, and the Strength of the Lithosphere

Constraints on the Rheology of the Lithosphere From Flexure of the Pacific Plate at the Hawaiian Islands

Dislocation creep of olivine: Backstress evolution controls transient creep at high temperatures

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