Evidence for {100}&lt;011&gt; slip in ferropericlase in Earth's lower mantle from high-pressure/high-temperature experiments

Immoor, Julia; Marquardt, Hauke; Miyagi, Lowell; Lin, Fan‐Chi; Speziale, S.; Merkel, Sébastien; Buchen, Johannes; Kurnosov, Alexander; Liermann, Hanns‐Peter

doi:10.1016/j.epsl.2018.02.045

Cited by 27 publications

(51 citation statements)

References 54 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Here we choose n = 3 for bridgmanite and postperovskite following Wenk et al (2006, 2011). Ferropericlase appears to have a slightly higher stress exponent (e.g., Stretton et al, 2001); therefore, we chose a stress exponent of n = 5, as was done in Immoor et al (2018). As noted in Immoor et al (2018), increasing the stress exponent by 1 or 2 does not have a significant effect on texture evolution.…”

Section: Methodsmentioning

confidence: 99%

“…In an attempt to create a consistent and comprehensive library, we invoked recent and plausible results on the most probable dominant slip systems for each proposed mineral. For ferropericlase elasticity, we test dominant {100}<011> slip using CRSS values from Immoor et al (2018), which is preferred for higher temperatures in the lower mantle. We also include lower temperature dominant {110}<1–10> slip using the CRSS values of Lin et al (2019).…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

A Library of Elastic Tensors for Lowermost Mantle Seismic Anisotropy Studies and Comparison With Seismic Observations

Creasy

Miyagi

Long

2020

Geochem Geophys Geosyst

View full text Add to dashboard Cite

The exact mechanism for lowermost mantle seismic anisotropy remains unknown; however, work on the elasticity and deformation of lower mantle materials has constrained a few possible options. The most probable minerals producing anisotropy are bridgmanite, postperovskite, and ferropericlase. While there is an extensive literature on the elasticity and deformation of lower mantle minerals, we create a comprehensive uniform database of D″ anisotropy scenarios. In order to characterize a range of the possible fabrics for D″ anisotropy, we carry out VPSC (visco-plastic self-consistent modeling) to predict textures for each proposed mineral and dominant slip system. We numerically deform each mineral under different geometrical scenarios: simple shear, pure shear, and extension. By using published single crystal elasticity values, we produce a library of 336 candidate elastic tensors. We used the elastic tensor library to revisit previously published D″-associated seismic anisotropy studies for crossing raypaths (Siberia, North America, the Afar region of Africa, and Australia). While we cannot identify a single, unique mechanism that explains all of these data sets, we find that postperovskite (dominant slip on [100](010) or [100](001)) and periclase (dominant slip on {100}<011>) provide the best fit to the observations and suggest reasonable shear directions for each region of interest. Bridgmanite generally provides a poor fit to the observations; however, we cannot completely rule out any particular model. As the number of anisotropy observations for D″ increases, this elastic tensor library will be helpful for observational seismologists in identifying possible mechanisms of anisotropy and shear directions at in the lowermost mantle.Plain-Language Summary At 2,800 km below the Earth's surface, minerals are being deformed under the high pressures, temperatures, and stresses of the deep mantle. A seismic phenomenon (seismic anisotropy) has been observed within this region, likely due to the deformation of some unknown mineral. There have been three proposed minerals based on experimental and theoretical work. As a result, we create a library of proposed mechanisms of this anisotropy by numerically calculating a series of plausible deformed rocks with a code called VPSC (viscoplastic self-consistent modeling). We have established an open-source library of elastic tensors (plausible deformed rocks) for all of the proposed minerals. We compare this library to data that have been previously observed near the core-mantle boundary (Siberia, North America, the Afar region of Africa, and Australia). We find that some of the tensors cannot consistently fit all of the available data sets (such as bridgmanite-the most abundant mineral in the lower mantle). However, two of the minerals can fit all of the data quite well (postperovskite and ferropericlase). Postperovskite is a result of bridgmanite changing its structure due to the high pressures and temperatures, approximately 200 km above the core-mantle boundary, and the lowe...

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

A Library of Elastic Tensors for Lowermost Mantle Seismic Anisotropy Studies and Comparison With Seismic Observations

Creasy

Miyagi

Long

2020

Geochem Geophys Geosyst

View full text Add to dashboard Cite

show abstract

“…Finally, the recent study of Immoor and coworkers [270] shows the compression textures of (Mg,Fe)O up to combined pressures and temperatures of 80 GPa and 1400 K. These experiments indicate a shift from a 001 to a combined (001 + 011) compression texture maximum as pressure and temperature increase. The texture transition, which could be assigned to a change from dominant {110} to dominant {100} slip is observed at~1400 K at low pressure and for pressures above 50 GPa at~1200 K. The effect of hydrostatic pressure on MgO plasticity was first investigated up to 1 GPa and 750 • C [271,272].…”

Section: Figure 32mentioning

confidence: 97%

“…At present, works are under way to extend the measurements into several directions: (i) larger P, T, and composition ranges [245,270]; (ii) finer interpretation of the experimental data with polycrystal plasticity models [253]; and (iii) complex deformation history, such as sinusoidal oscillations [283]. These works will allow, in the future, clarifying the combined effects of P and T on MgO and (Mg,Fe)O plasticity.…”

Section: Experimental Identification Of Individual Deformation Mechanmentioning

confidence: 99%

Dislocations and Plastic Deformation in MgO Crystals: A Review

et al. 2018

View full text Add to dashboard Cite

This review paper focuses on dislocations and plastic deformation in magnesium oxide crystals. MgO is an archetype ionic ceramic with refractory properties which is of interest in several fields of applications such as ceramic materials fabrication, nano-scale engineering and Earth sciences. In its bulk single crystal shape, MgO can deform up to few percent plastic strain due to dislocation plasticity processes that strongly depend on external parameters such as pressure, temperature, strain rate, or crystal size. This review describes how a combined approach of macro-mechanical tests, multi-scale modeling, nano-mechanical tests, and high pressure experiments and simulations have progressively helped to improve our understanding of MgO mechanical behavior and elementary dislocation-based processes under stress.

show abstract

“…In a lower mantle of pyrolitic composition, bridgmanite is expected to compose the largest part of the lower mantle (with estimates ranging from approximately 70-90%), followed by ferropericlase and calcium silicate perovskite (e.g., Hirose et al, 2017;Stixrude & Lithgow-Bertelloni, 2012). It has been suggested that the rheology of the Earth's lower mantle is governed by the rheology of its two main constituents bridgmanite and ferropericlase; however, both rheologies are not very well known at lower mantle conditions and are subject of active research (e.g., Girard et al, 2016;Immoor et al, 2018;Kaercher et al, 2016;Merkel et al, 2003;Miyagi & Wenk, 2016;Reali et al, 2019). The rheology of calcium silicate perovskite is even less known due to experimental difficulties (Miyagi et al, 2009;Nestola et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Ferropericlase Control of Lower Mantle Rheology: Impact of Phase Morphology

Thielmann

Golabek

Marquardt

2020

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Evidence for {100}<011> slip in ferropericlase in Earth's lower mantle from high-pressure/high-temperature experiments

Cited by 27 publications

References 54 publications

A Library of Elastic Tensors for Lowermost Mantle Seismic Anisotropy Studies and Comparison With Seismic Observations

A Library of Elastic Tensors for Lowermost Mantle Seismic Anisotropy Studies and Comparison With Seismic Observations

Dislocations and Plastic Deformation in MgO Crystals: A Review

Ferropericlase Control of Lower Mantle Rheology: Impact of Phase Morphology

Contact Info

Product

Resources

About