Defining a proxy for the interpretation of seismic anisotropy in non‐Newtonian mantle flows

Hedjazian, Navid; Kaminski, É.

doi:10.1002/2014gl061372

Cited by 11 publications

(8 citation statements)

References 41 publications

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“…Measurements of seismic anisotropy provide a means to learn about oceanic plate formation and mantle flow. This is possible because the evolution of lithospheric anisotropy is sensitive to a variety of factors including preexisting mantle fabric (Boneh & Skemer, ; Skemer et al, ), the amount of strain the lithosphere experiences (e.g., Hedjazian & Kaminski, ; Ribe, ; Zhang & Karato, ), the magnitude of shear strain relative to the rate of rotation of the strain axes (Kaminski & Ribe, ), and the presence of melt during deformation (Hansen et al, ; Qi et al, ). At the same time, this variety of sensitivities can make the interpretation of anisotropy difficult.…”

Section: Discussionmentioning

confidence: 99%

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

et al. 2019

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Plate formation and evolution processes are predicted to generate upper mantle seismic anisotropy and negative vertical velocity gradients in oceanic lithosphere. However, predictions for upper mantle seismic velocity structure do not fully agree with the results of seismic experiments. The strength of anisotropy observed in the upper mantle varies widely. Further, many refraction studies observe a fast direction of anisotropy rotated several degrees with respect to the paleospreading direction, suggesting that upper mantle anisotropy records processes other than 2‐D corner flow and plate‐driven shear near mid‐ocean ridges. We measure 6.0 ± 0.3% anisotropy at the Moho in 70‐Ma lithosphere in the central Pacific with a fast direction parallel to paleospreading, consistent with mineral alignment by 2‐D mantle flow near a mid‐ocean ridge. We also find an increase in the strength of anisotropy with depth, with vertical velocity gradients estimated at 0.02 km/s/km in the fast direction and 0 km/s/km in the slow direction. The increase in anisotropy with depth can be explained by mechanisms for producing anisotropy other than intrinsic effects from mineral fabric, such as aligned cracks or other structures. This measurement of seismic anisotropy and gradients reflects the effects of both plate formation and evolution processes on seismic velocity structure in mature oceanic lithosphere, and can serve as a reference for future studies to investigate the processes involved in lithospheric formation and evolution.

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Section: Discussionmentioning

confidence: 99%

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

et al. 2019

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“…Lin and Kuo (; LK16) compared measured ϕ with the infinite strain axis (ISA), a proxy of the finite strain orientation (Hedjazian & Kaminski, ; Jadamec & Billen, ), in the dynamic model and proposed that ϕ can be explained by strain field in the asthenosphere. In the present study, we take a new approach: the observed ϕ and the ISA azimuth ψ are compared along the SKS path, rather than at the station as though the path is exactly vertical.…”

Section: Model Prediction Of ϕmentioning

confidence: 99%

SKS Splitting and the Scale of Vertical Coherence of the Taiwan Mountain Belt

Kuo

Lin

Lin³

2018

JGR Solid Earth

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Many continental orogens feature a pattern of SKS shear wave splitting with fast polarization directions parallel to the mountain fabrics and delay times of 1–2 s, implying that the crust and lithosphere deform consistently. In the Taiwan arc‐continent collision zone, similar pattern of SKS splitting exists, and thereby lithospheric scale deformation due to collision has been assumed. However, recent dynamic modeling demonstrated that the SKS splitting in Taiwan can be generated by the toroidal flow in the asthenosphere induced by the subduction of the Philippine Sea plate and the Eurasian plate. To further evaluate this hypothesis, we analyzed a new data set using a quantitative approach. The results show that models with slab geometries constrained by seismicity explain the observed fast splitting direction to within 25°, whereas the misfit grows to ~50–60° if the toroidal flow is disrupted by the presence of a sizable aseismic slab beneath central Taiwan as often suggested by tomographic imaging. However, small sized aseismic slab or detached slab fragment can potentially reconcile the splitting observations. We estimated the scale of vertical coherence to be 10–40 km in the lithosphere and 100–150 km in the asthenosphere, making the former unfavorable for accumulating large delay times. The low coherence is caused by the subduction of the Eurasian plate that creates complex deformation different from what characterizes the compressional tectonics above the plate. This suggests that the mountain building in Taiwan is a shallow process, rather than lithospheric in scale.

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“…For D-Rex, two nondimensional parameters, M* and λ*, are used to simulate dynamic recrystallization via grain boundary migration and nucleation of strain-free grains, respectively. Both parameters influence textural evolution, but M* is most dominant in determining the overall influence of dynamic recrystallization on texture [e.g., Hedjazian and Kaminski, 2014]. Many prior studies have used M* = 125, the value suggested by Kaminski and Ribe [2001] based on comparisons to the experimental results of Zhang and Karato [1995].…”

Section: Implementation Of Previously Published Modelsmentioning

confidence: 99%

Viscous anisotropy of textured olivine aggregates: 2. Micromechanical model

et al. 2016

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The significant viscous anisotropy that results from crystallographic alignment (texture) of olivine grains in deformed upper mantle rocks strongly influences a large variety of geodynamic processes. Our ability to explore the effects of anisotropic viscosity in simulations of these processes requires a mechanical model that can predict the magnitude of anisotropy and its evolution. Unfortunately, existing models of olivine textural evolution and viscous anisotropy are calibrated for relatively small deformations and simple strain paths, making them less general than desired for many large‐scale geodynamic scenarios. Here we develop a new set of micromechanical models to describe the mechanical behavior and textural evolution of olivine through a large range of strains and complex strain histories. For the mechanical behavior, we explore two extreme scenarios, one in which each grain experiences the same stress tensor (Sachs model) and one in which each grain undergoes a strain rate as close as possible to the macroscopic strain rate (pseudo‐Taylor model). For the textural evolution, we develop a new model in which the director method is used to control the rate of grain rotation and the available slip systems in olivine are used to control the axis of rotation. Only recently has enough laboratory data on the deformation of olivine become available to calibrate these models. We use these new data to conduct inversions for the best parameters to characterize both the mechanical and textural evolution models. These inversions demonstrate that the calibrated pseudo‐Taylor model best reproduces the mechanical observations. Additionally, the pseudo‐Taylor textural evolution model can reasonably reproduce the observed texture strength, shape, and orientation after large and complex deformations. A quantitative comparison between our calibrated models and previously published models reveals that our new models excel in predicting the magnitude of viscous anisotropy and the details of the textural evolution. In addition, we demonstrate that the mechanical and textural evolution models can be coupled and used to reproduce mechanical evolution during large‐strain torsion tests. This set of models therefore provides a new geodynamic tool for incorporating viscous anisotropy into large‐scale numerical simulations.

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Defining a proxy for the interpretation of seismic anisotropy in non‐Newtonian mantle flows

Cited by 11 publications

References 41 publications

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

Azimuthal Seismic Anisotropy of 70‐Ma Pacific‐Plate Upper Mantle

SKS Splitting and the Scale of Vertical Coherence of the Taiwan Mountain Belt

Viscous anisotropy of textured olivine aggregates: 2. Micromechanical model

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