Modelling the bulk viscosity of two-phase mixtures in terms of clast shape

Treagus, Susan H.

doi:10.1016/s0191-8141(01)00049-9

Cited by 61 publications

(38 citation statements)

References 30 publications

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“…The Voigt model is considered an upper bound (discussed by Ji, 2004) but predicts significantly greater η eff for jammed mélange than our models (Figure 1a). The initial orientation of the clasts has a negligible impact on the degree of strengthening at ϵ xy = 1.75 (Figure 2a, red circle), contrary to the emphasis in previous studies (e.g., Treagus, 2002). This is because, at least for a relatively high ϕ = 0.64, clasts can jam while remaining subhorizontal (Figure 1).…”

Section: 1029/2018gl081252contrasting

confidence: 60%

Strength of Strained Two‐Phase Mixtures: Application to Rapid Creep and Stress Amplification in Subduction Zone Mélange

Beall

Fagereng

Ellis

2019

Geophysical Research Letters

106

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Aseismic creep may occur by distributed deformation in mélange shear zones comprising weak matrix and stronger clast materials. Slow slip events or steady tectonic displacement can be distributed over <100‐m thick shear zones if weak matrix controls bulk shear zone deformation. We use 2‐D numerical models to quantify the rheology of moderately strained (shear strain <1.75) mélange for various volumetric proportions of competent clasts. Mélange deformation with <50% clasts is matrix dominated and can accommodate steady creep. At higher clast proportions mélange viscosity increases more than tenfold after small strains, because strong clasts interact and form force chains. Clast shear stress is amplified above the imposed shear stress, by a factor of <14 where force chains develop. Slow slip events may occur due to a temporary absence of force chains, while localized regions of high shear stress generate coincident fracturing and potentially tremor events.

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Section: 1029/2018gl081252contrasting

confidence: 60%

Strength of Strained Two‐Phase Mixtures: Application to Rapid Creep and Stress Amplification in Subduction Zone Mélange

Beall

Fagereng

Ellis

2019

Geophysical Research Letters

106

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“…Mixing laws and continuum mechanics models are often used to predict particle reinforcement of a ductile matrix [ Chen and Argon , 1979; Berveiller and Zaoui , 1984; Cho and Gurland , 1988; Yoon and Chen , 1990; Tanaka et al , 1991; Ravichandran and Seetharaman , 1993; Treagus , 2002]. In these models, load sharing between matrix and particles is a central assumption.…”

Section: Discussionmentioning

confidence: 99%

Rheology of synthetic anorthite‐diopside aggregates: Implications for ductile shear zones

2005

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[1] We investigated the high-temperature creep strength of fine-grained anorthite-diopside rocks at temperatures ranging from 1323 K to 1523 K and at 300 MPa confining pressure in a Paterson-type gas-medium deformation apparatus. Flow stress varied between 20 and 450 MPa resulting in strain rates between 6.1 Â 10 À7 s À1 and 7.5 Â 10 À4 s À1 . Pure diopside and anorthite samples were hot pressed from crushed natural single crystals and glass powders, respectively. Two-phase samples were produced by hot isostatic pressing of mechanically mixed powders of anorthite glass with 25, 50 and 75 vol % diopside particles. Arithmetic mean grain size of the anorthite matrix is d An % 3.5 mm. Three different ranges of diopside particle size were used: d Di < 25 mm, <35 mm, and <45 mm. Water content of as is samples was about 0.05 ± 0.02 wt % H 2 O, and predried samples contain about 0.004 ± 0.001 wt % H 2 O. At experimental conditions, as is samples are assumed to be water saturated. Water content of predried samples is about 3 times less than that of starting diopside single crystals. The specimens contain about 1 vol % glass located at fluid inclusions and some multiple grain junctions. Two-grain boundaries examined by high-resolution transmission electron microscopy did not show amorphous layers to a resolution of 1 nm. At experimental conditions, pure diopside aggregates are about 2-3 orders of magnitude stronger than pure anorthite samples for as is and predried specimens, respectively. In general, strength of the two-phase aggregates increases with increasing diopside content but remains between isostress and isostrain rate bounds. Aggregate strengths predicted from continuum mechanics models are in good agreement with the experimental data for dilute diopside particle mixtures and highvolume fractions, when diopside particles form a load-bearing framework. At low stresses (<100-200 MPa) the stress exponent is n % 1, suggesting diffusion-controlled creep. At higher stresses, mechanical data and microstructures suggest that samples deformed in the transition region between diffusion-controlled creep and dislocation creep. For pure anorthite and diopside aggregates deforming in dislocation creep we estimated stress exponents of n % 3 and n % 5.5, respectively. For the two-phase aggregates, n is between n % 3 and n % 5, depending on diopside content. At low stresses, deformation microstructures indicate load transfer from a weak anorthite matrix to stronger diopside particles. Creep activation energies for pure diopside and anorthite mixtures range from 286 kJ mol À1 for wet anorthite deformed at low stresses to 691 kJ mol À1 for dry diopside deformed at high stresses. Activation energies of two-phase mixtures are between or close to those of the end-members. As is samples have significantly lower activation energies than predried samples.Citation: Dimanov, A., and G. Dresen (2005), Rheology of synthetic anorthite-diopside aggregates: Implications for ductile shear zones,

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“…Under large deformation, bulk composite materials can undergo a transition from the initial LBF texture to IWL by developing SPO (e.g., Handy, 1994a;Holyoke and Tullis, 2006;Takeda and Griera, 2006). The materials science, mechanical engineering, and structural geology literature provides a wealth of information on models of the mechanical behaviors of composite materials (e.g., Guoan and Castañeda, 1993;Lee and Paul, 2005;Tandon and Weng, 1986;Fletcher, 2004;Handy, 1994a;Kanagawa, 1993;Treagus, 2002). Experimental efforts have also yielded valuable information on the mechanical behavior of crustal rocks and rock analogs (e.g., Jordan, 1987;Shea and Kronenberg, 1993;Holyoke and Tullis, 2006), by relating stress-strain curves with textural information.…”

Section: Introductionmentioning

confidence: 99%

In situ high-pressure and high-temperature X-ray microtomographic imaging during large deformation: A new technique for studying mechanical behavior of multiphase composites

et al. 2011

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International audiencemicrostructural evolution of a two-phase composite (olivine + Fe-Ni-S) during large shear deformation, using a newly developed high-pressure X-ray tomography microscope. Two samples were examined: a load-bearing framework-type texture, where the alloy phase (Fe-Ni-S) was present as isolated spherical inclusions, and an interconnected network-type texture, where the alloy phase was concentrated along the silicate grain boundaries and tended to form an interconnected network. The samples, both containing ~10 vol% alloy inclusions, were compressed to 6 GPa, followed by shear deformation at temperatures up to 800 K. Shear strains were introduced by twisting the samples at high pressure and high temperature. At each imposed shear strain, samples were cooled to ambient temperature and tomographic images collected. The three-dimensional tomographic images were analyzed for textural evolution. We found that in both samples, Fe-Ni-S, which is the weaker phase in the composite, underwent signifi cant deformation. The resulting lens-shaped alloy phase is subparallel to the shear plane and has a laminated, highly anisotropic interconnected weak layer texture. Scanning electron microscopy showed that many alloy inclusions became fi lm-like, with thicknesses <1 m, suggesting that Fe- Ni-S was highly mobile under nonhydrostatic stress, migrated into silicate grain bound aries, and propagated in a manner similar to melt inclusions in a deforming solid matrix. The grain size of the silicate matrix was signifi cantly reduced under large strain deformation. The strong shape-preferred orientation thus developed can profoundly influence a composite's bulk elastic and rheological properties. High-pressure-high temperature tomography not only provides quantitative observations on textural evolution, but also can be compared with simulation results to derive more rigorous models of the mechanical properties of composite materials relevant to Earth's deep mantle

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Modelling the bulk viscosity of two-phase mixtures in terms of clast shape

Cited by 61 publications

References 30 publications

Strength of Strained Two‐Phase Mixtures: Application to Rapid Creep and Stress Amplification in Subduction Zone Mélange

Strength of Strained Two‐Phase Mixtures: Application to Rapid Creep and Stress Amplification in Subduction Zone Mélange

Rheology of synthetic anorthite‐diopside aggregates: Implications for ductile shear zones

In situ high-pressure and high-temperature X-ray microtomographic imaging during large deformation: A new technique for studying mechanical behavior of multiphase composites

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