Effect of phase morphology on bulk strength for power-law materials

Gerbi, Christopher; Johnson, Scott E.; Cook, Alden C.; Vel, Senthil S.

doi:10.1093/gji/ggu388

Cited by 17 publications

(18 citation statements)

References 56 publications

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“…2b) displays that as the IWLs form in the other geometries, the material strength evolves towards that of horizontal geometry, irrespective of the initial weak geometry, confirming that layers of weak components parallel to the shear direction represent the weakest geometry (e.g. Cook et al, 2014;Dell'Angelo and Tullis, 1996;Gerbi et al, 2015;Holyoke III and Tullis, 2006).…”

Section: Influence Of Geometry On Materials Strengthmentioning

confidence: 82%

“…Dell'Angelo and Tullis, 1996;Holyoke III and Tullis, 2006) and numerical tests (e.g. Cook et al, 2014;Gerbi et al, 2015) showing the horizontal geometry is weakest; (ii) the experiments of Shea and Kronenberg (1993) who show, similar to our vertical striped geometry, that a 45° angle of the weak phase to the shear direction is the strongest; (iii) all model strengths fall between the calculated iso-stress and iso-strain bounds (e.g. Treagus, 2002) with the horizontal geometry very close to the iso-strain boundary ( Supplementary Fig.…”

Section: General Validity Of the Numerical Modelmentioning

confidence: 99%

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Patterns of strain localization in heterogeneous, polycrystalline rocks – a numerical perspective

Gardner

Piazolo

Evans

et al. 2017

Earth and Planetary Science Letters

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including the URL of the record and the reason for the withdrawal request. Highlights  Shear zones are difficult to form without a dynamic weakening mechanism  Dynamic weakening can quickly localize strain into an interconnected weak zone  Competing weakening and strengthening processes impact shear zone pattern  Shear zones are dynamic in time and space within a single deformation event  Finite strain patterns do not fully represent the evolution of a shear zone network *Highlights (for review)

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Section: Influence Of Geometry On Materials Strengthmentioning

confidence: 82%

Section: General Validity Of the Numerical Modelmentioning

confidence: 99%

Patterns of strain localization in heterogeneous, polycrystalline rocks – a numerical perspective

Gardner

Piazolo

Evans

et al. 2017

Earth and Planetary Science Letters

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“…This is partially due to the increase in weak phase proportion (Figures 5e and 5f) but, importantly, is also due to the development of the weak layer parallel to the shearing direction. This horizontal weak layer geometry has been shown to be comparatively the weakest geometry by many experiments both analog (e.g., Dell'Angelo & Tullis, 1996;Holyoke & Tullis, 2006) and numerical (e.g., Cook et al, 2014;Gardner et al, 2017;Gerbi et al, 2015).…”

Section: Localized Anastomosing or Distributed Strain: An Effect Ofmentioning

confidence: 93%

Ductile Deformation Without Localization: Insights From Numerical Modeling

Gardner

Piazolo

Daczko

et al. 2019

Geochem Geophys Geosyst

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Strain is easily localized in a polyphase rock, especially if the rock undergoes syntectonic weakening processes. However, there is ample field evidence for distributed, rather than localized, deformation at the outcrop to hundreds of square kilometer scale. In these areas, distributed strain is evidenced by the presence of continuous foliations and a lack of distinct high-strain zones. Here, we use numerical modeling of viscous deformation to investigate the conditions that allow distributed rather than localized deformation. We identify three strain localization regimes for a system with rheologically strong and weak phases with or without stress-induced weakening. Regime I is characterized by distributed strain. It forms where either deformation-induced interconnection of the weak phase is not possible or the initial weak phase area is intermediate to high (i.e., >~40-60% of total depending on weak phase geometry). Their resultant bulk strength is either strong or weak, respectively. Regime II is characterized by variably distributed areas of strain localization and develops if the initial proportion of weak phases is intermediate (i.e., 40-60% weak phase depending on geometry) and syntectonic weakening causes an increase (up to~12%) of weak phase proportion. Regime III exhibits significant strain localization and only develops if the initial proportion of weak phases is relatively low (<20%) and syntectonic weakening increases the proportion of weak phases by over~12%. Here, high-strain zones readily form irrespective of the initial distribution of rheologically weak and hard phases, and bulk strength is intermediate. Plain Language SummaryOver many years, scientists have concentrated on the question of how deformation is localized in zones of high strain. Hence, areas without these zones, where deformation is distributed, have not been given much attention. This is because it has often been assumed that these areas were insignificant in terms of how deformation is accommodated. In this research we take a different approach and ask the question: "Under what conditions does deformation remain distributed rather than become localized?" To find out, we have run a series of computer simulations testing scenarios that allow or do not allow distributed deformation to occur. If there is a mix of weak and strong phases, for example, two different types of rocks or minerals (as typical in the Earth), then there are two main requirements to form areas of distributed strain: (i) the proportion of weak phases is either high or low (i.e., not intermediate) and (ii) there is no way the strong phase can become weakened. Our results are important for the interpretation of areas that show distributed strain and their significance in the overall deformation of the Earth's crust and mantle.

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“…For this reason, past numerical studies of such systems have attempted to develop a parameterization of the impact of weak phase topology on the effective rheology for specific inclusion shapes such as layers, squares, or ellipses (e.g., Dabrowski et al, ; Fletcher, ; Handy, , ; Takeda, ; Takeda & Griera, ; Treagus, ; Tullis et al, ). More recently, both Cook et al () and Gerbi et al () also considered the effect of more complex morphologies on the effective rheology of power law materials.…”

Section: Introductionmentioning

confidence: 99%

Ferropericlase Control of Lower Mantle Rheology: Impact of Phase Morphology

Thielmann

Golabek

Marquardt

2020

Geochem Geophys Geosyst

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The rheological properties of Earth's lower mantle play a key role for global mantle dynamics. The mineralogy of the lower mantle can be approximated as a bridgmanite‐ferropericlase mixture. Previous work has suggested that the deformation of this mixture might be dramatically affected by the large differences in viscosity between bridgmanite and ferropericlase. Here, we employ numerical models to establish a connection between ferropericlase morphology and the effective rheology of the Earth's lower mantle using a numerical‐statistical approach. Using this approach, we link the statistical properties of the two‐phase composite to its effective viscosity tensor using analytical approximations. We find that ferropericlase develops elongated structures within the bridgmanite matrix that result in significantly lowered viscosity. While our findings confirm previous endmember models that suggested a change of mantle viscosity due to the formation of interconnected weak layers, we show that significant rheological weakening can thus be already achieved even when ferropericlase does not form an interconnected network. Additionally, the alignment of weak ferropericlase leads to a pronounced viscous anisotropy that develops with total strain, which may have implications for understanding the viscosity structure of Earth's lower mantle as well as for modeling the behavior of subducting slabs. We show that to capture the effect of ferropericlase elongation on the effective viscosity tensor (and its anisotropy) in large‐scale mantle convection models, the analytical approximations that have been derived to describe the evolution of the effective viscosity of a two‐phase medium with aligned elliptical inclusions can be used.

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Effect of phase morphology on bulk strength for power-law materials

Cited by 17 publications

References 56 publications

Patterns of strain localization in heterogeneous, polycrystalline rocks – a numerical perspective

Patterns of strain localization in heterogeneous, polycrystalline rocks – a numerical perspective

Ductile Deformation Without Localization: Insights From Numerical Modeling

Ferropericlase Control of Lower Mantle Rheology: Impact of Phase Morphology

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