Competing Deformation Mechanisms in Periclase: Implications for Lower Mantle Anisotropy

Feng Lin,Samantha Couper,Mike Jugle,Lowell Miyagi

doi:10.3390/min9110650

Feng Lin, Samantha Couper + Show 2 more

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https://doi.org/10.3390/min9110650

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Journal: Minerals	Publication Date: Oct 23, 2019
Citations: 11	License type: CC BY 4.0

Affiliation: University of Utah, United States Geological Survey

Abstract

Seismic anisotropy is observed above the core-mantle boundary in regions of slab subduction and near the margins of Large Low Shear Velocity Provinces (LLSVPs). Ferropericlase is believed to be the second most abundant phase in the lower mantle. As it is rheologically weak, it may be a dominant source for anisotropy in the lowermost mantle. Understanding deformation mechanisms in ferropericlase over a range of pressure and temperature conditions is crucial to interpret seismic anisotropy. The effect of temperature on deformation mechanisms of ferropericlase has been established, but the effects of pressure are still controversial. With the aim to clarify and quantify the effect of pressure on deformation mechanisms, we perform room temperature compression experiments on polycrystalline periclase to 50 GPa. Lattice strains and texture development are modeled using the Elasto-ViscoPlastic Self Consistent method (EVPSC). Based on modeling results, we find that { 110 } ⟨ 1 1 ¯ 0 ⟩ slip is increasingly activated with higher pressure and is fully activated at ~50 GPa. Pressure and temperature have a competing effect on activities of dominant slip systems. An increasing { 100 } ⟨ 011 ⟩ : { 110 } ⟨ 1 1 ¯ 0 ⟩ ratio of slip activity is expected as material moves from cold subduction regions towards hot upwelling region adjacent to LLSVPs. This could explain observed seismic anisotropy in the circum-Pacific region that appears to weaken near margins of LLVSPs.

Highlights

Shear wave splitting is widely used to document seismic anisotropy in the lower mantle
Anisotropy is widely observed above the core-mantle boundary (CMB) near regions of slab subduction and adjacent to the borders of Large Low Shear Velocity Provinces (LLVSPs)
Understanding the deformation mechanisms of the ferropericlase at D” conditions is of great importance for understanding sources of anisotropy in the lower mantle

Summary

Introduction

Shear wave splitting is widely used to document seismic anisotropy in the lower mantle. Understanding the deformation mechanisms of the ferropericlase at D” conditions is of great importance for understanding sources of anisotropy in the lower mantle. High pressure single crystal deformation experiments trends in slip system strengths consistent with a change. This study did not document a significant change in texture evolution, and as such, the deformation mechanism responsible for the increase in flow stress was not identified. E same composition of ferropericlase as [36] shows evidence of comparable activation of both {110} 110 and {100}h011i slip systems at ~1400 K in a range of 30–60 GPa [37]. In order to quantify the effect of pressure on deformation mechanisms and to understand the role of Fe changes in deformation mechanisms, we performed two DAC compression experiments on polycrystalline periclase up to 50 GPa at room temperature. Lattice strains and texture evolution at varying pressures are recorded using radial diffraction geometry and modeled as a function of slip system activities using the Elasto-ViscoPlastic Self Consistent method (EVPSC)

Experiment Details

Experiment Data Analysis components as

Plasticity Simulations

Results and Discussion

Inverse