Predicting viscoplastic anisotropy in the upper mantle: a comparison between experiments and polycrystal plasticity models

Mameri, Lucan; Tommasi, Andréa; Signorelli, Javier; Hansen, Louis S.

doi:10.1016/j.pepi.2018.11.002

Cited by 15 publications

(6 citation statements)

References 49 publications

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“…Tommasi et al, 2000;Mameri et al, 2019). Other processes than pure dislocation or diffusion creep, such as coupled grain boundary migration and shear (Mompiou et al, 2009;Cordier et al, 2014) or grain-boundary sliding (e.g., Maruyama and Hiraga, 2017) may also play a role during the deformation of a polycrystalline aggregate at depth.…”

Section: Constraining Effective Mantle Viscosity Using Geodynamical Simulationsmentioning

confidence: 99%

Using thermo-mechanical models of subduction to constrain effective mantle viscosity

Garel

Thoraval

Tommasi

et al. 2020

Earth and Planetary Science Letters

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Mantle convection and plate dynamics transfer and deform solid material on scales of hundreds to thousands of km. However, viscoplastic deformation of rocks arises from motions of defects at subcrystal scale, such as vacancies or dislocations. In this study, results from numerical experiments of dislocation dynamics in olivine for temperatures and stresses relevant for both lithospheric and asthenospheric mantle (800-1700 K and 50-500 MPa; Gouriet et al., 2019) are used to derive three sigmoid parameterizations (erf, tanh, algebraic), which express stress evolution as a function of temperature and strain rate. The three parameterizations fit well the results of dislocation dynamics models and may be easily incorporated into geodynamical models. Here, they are used in an upper mantle thermo-mechanical model of subduction, in association with diffusion creep and pseudo-brittle flow laws. Simulations using different dislocation creep parameterizations exhibit distinct dynamics, from unrealistically fast-sinking slabs in the erf case to very slowly-sinking slabs in the algebraic case. These differences could not have been predicted a priori from comparison with experimentally determined mechanical data, since they principally arise from feedbacks between slab sinking velocity, temperature, drag, and buoyancy, which are controlled by the strain rate dependence of the effective asthenosphere viscosity. Comparison of model predictions to geophysical observations and to uppermantle viscosity inferred from glacial isostatic adjustment shows that the tanh parameterization best fits both crystal-scale and Earth-scale constraints. However, the parameterization of diffusion creep is also important for subduction bulk dynamics since it sets the viscosity of slowly deforming domains in the convecting mantle. Within the range of uncertainties of experimental data and, most importantly, of the actual rheological parameters prevailing in the upper mantle (e.g. grain size, chemistry), viscosity enabling realistic mantle properties and plate dynamics may be reproduced by several combinations of parameterizations for different deformation mechanisms. Deriving mantle rheology cannot therefore rely solely on the extrapolation of semi-empirical flow laws. The present study shows that thermo-mechanical models of plate and mantle dynamics can be used to constrain the effective rheology of Earth's mantle in the presence of multiple deformation mechanisms.

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Section: Constraining Effective Mantle Viscosity Using Geodynamical Simulationsmentioning

confidence: 99%

Using thermo-mechanical models of subduction to constrain effective mantle viscosity

Garel

Thoraval

Tommasi

et al. 2020

Earth and Planetary Science Letters

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“…Another limitation is there is no cap on texture strength such as that expected to occur from dynamic recrystallisation as dislocation density increases. Not limiting texture strength in our model may lead to geometric hardening where high CPO intensity becomes harder to texture further as has been previously shown in olivine (Hansen et al, 2012;Mameri et al, 2019), which could limit the formation of future texture. Capping texture strength with some form of dynamic recrystallisation or in an ad-hoc way by reducing the velocity gradient magnitude at each step along the path (e.g.…”

Section: Modelling Assumptionsmentioning

confidence: 78%

“…We suggest easier-to-texture polycrystals hold more texturing from past flow in our setup because of the di culty to re-texture a heavily shearstrained polycrystal. If the polycrystal experiences high strain rates early in its path, an easy-to-texture material will be heavily textured and geometric hardening, where the material hardness increases with plastic deformation (Hansen et al, 2012;Mameri et al, 2019), will make new texturing more di cult.…”

Section: The E↵ect Of Ease-of-texturing On Past Flow Influencementioning

confidence: 99%

The sensitivity of lowermost mantle anisotropy to past mantle convection

Ward,

Walker,

Nowacki

et al. 2024

Preprint

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It is widely believed that seismic anisotropy in the lowermost mantle is caused by the flow-induced alignment of anisotropic crystals such as post-perovskite. What is unclear, however, is whether the anisotropy observations in the lowermost mantle hold information about past mantle flow, or if they only inform us about the present-day flow field. To investigate this, we compare the general and seismic anisotropy calculated using Earth-like mantle convection models where one has a time-varying flow, and another where the present-day flow is constant throughout time. To do this, we track a post-perovskite polycrystal through the flow fields and calculate texture development using the sampled strain rate and the visco-plastic self-consistent approach. As texture development also depends on the slip systems assumed, we compare the results of the flow fields under three ease-of-texturing slip system test cases. We compare the radial anisotropy parameters and the anisotropic components of the elastic tensors produced by the flow field test cases at the same location. We find, under all ease-of-texturing cases, the radial anisotropy is very similar (difference < 2%) in the majority of locations and in some regions, the difference can be very large (> 10%). The same is true when comparing the elastic tensors directly. Varying the ease-of-texture development in the crystal aggregate suggests that easier-to-texture material may hold a stronger signal from past flow than harder-to-texture material. Our results imply that broad-scale observations of seismic anisotropy such as those from seismic tomography, 1-D estimates and normal mode observations, will be mainly sensitive to present-day flow. Shear-wave splitting measurements, however, could hold information about past mantle flow. In general, mantle memory expressed in anisotropy may be dependent on path length in the post-perovskite stability field. Our work implies that, as knowledge of the exact causative mechanism of lowermost mantle anisotropy develops, we may be able to constrain both present-day and past mantle convection.

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“…These data record patterns of active or old (fossilized) olivine textures, which are homogeneous at the scale of several tens to hundreds of km in the upper mantle. These textures produce viscoplastic anisotropy at large-scale (Knoll et al 2009;Hansen et al 2012;Mameri et al 2019), which in turn modifies subsequent deformation. Texture-induced viscous anisotropy has been proposed as a major feature of plate tectonics, explaining the reactivation of ancient structures, even at hundreds of million years of interval (Vauchez et al 1997;Tommasi and Vauchez 2001;Tommasi et al 2009).…”

Section: Introductionmentioning

confidence: 99%

An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows

Signorelli¹,

Hassani²,

Tommasi³

et al. 2021

Journal of Theoretical, Computational and Applied Mechanics

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In this article, we describe the mathematical formulation and the numerical implementation of an effective parametrization of the viscous anisotropy of orthorhombic materials produced by crystallographic preferred orientations (CPO or texture), which can be integrated into 3D geodynamic and materials science codes. Here, the approach is applied to characterize the texture-induced viscous anisotropy of olivine polycrystals, the main constituent of the Earth's upper mantle. The parameterization is based on the Hill (1948) orthotropic yield criterion. The coefficients of the Hill yield surface are calibrated based on numerical tests performed using the second order Viscoplastic Self-consistent (SO-VPSC) model. The parametrization was implemented in a 3D thermo-mechanical finite-element code developed to model large-scale geodynamical flows, in the form of a Maxwell rheology combining isotropic elastic and anisotropic non-linear viscous behaviors. The implementation was validated by comparison with results of the analytical solution and of the SO-VPSC model for simple shear and axial compression of a homogeneous anisotropic material. An application designed to examine the effect of texture-induced viscous anisotropy on the reactivation of mantle shear zones in continental plates highlights unexpected couplings between localized deformation controlled by variations in the orientation and intensity of the olivine texture in the mantle and the mechanical behavior of the elasto-viscoplastic overlying crust. Importantly, the computational time only increases by a factor 2-3 with respect to the classic isotropic Maxwell viscoelastic rheology. Comment: 32 pag.; 5 figures; 4 tables

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Predicting viscoplastic anisotropy in the upper mantle: a comparison between experiments and polycrystal plasticity models

Abstract: Predicting viscoplastic anisotropy in the upper mantle: a comparison between experiments and polycrystal plasticity models. Phys. Earth Planet.

Cited by 15 publications

References 49 publications

Using thermo-mechanical models of subduction to constrain effective mantle viscosity

Using thermo-mechanical models of subduction to constrain effective mantle viscosity

The sensitivity of lowermost mantle anisotropy to past mantle convection

An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows

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