Silicon and oxygen self-diffusion in stishovite: Implications for stability of SiO 2 -rich seismic reflectors in the mid-mantle

Xu, Fang; Sakamoto, Naoya; Sun, Wei; Fei, Hongzhan; Yurimoto, H.

doi:10.1016/j.epsl.2016.11.044

Cited by 17 publications

(18 citation statements)

References 38 publications

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“…The higher strength of stishovite indicates therefore that the dislocation mobility cannot be significantly greater in stishovite than in quartz or coesite and is probably much lower. This is consistent with very slow silicon and oxygen diffusion observed in stishovite (Xu et al, ). All three silica phases studied here are tectosilicates, so, unlike in olivine, Si‐O bonds must be broken and reformed for motion of dislocations to occur in the crystals.…”

Section: Discussionsupporting

confidence: 89%

“…Stishovite supports extremely high differential stresses during compression in the diamond anvil cell (Singh et al, ), and while it has been deformed to reasonable strain (Kaercher et al, ; Texier & Cordier, ), its rheology has not been measured. The high hardness of stishovite is likely to persist at high temperatures because of its extremely slow silicon diffusion (Shatskiy et al, ; Xu et al, ).…”

Section: Introductionmentioning

confidence: 99%

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An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

Hunt

Whitaker

Bailey

et al. 2019

Geochem Geophys Geosyst

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In this study, quartz, coesite, and stishovite were deformed concurrently with an olivine reference sample at high pressure and 850 ± 50 °C. Olivine deformed with an effective stress exponent (n) of 6.9−2.2+3.1, which we interpret to indicate that the Peierls creep deformation mechanism was active in the olivine. Quartz and coesite had very similar strengths and deformed by a mechanism with n = 2.8−0.9+1.2 and 2.9−0.9+1.3, respectively, which are consistent with previous measurements of power law creep in these phases. Stishovite deformed with n = 8.1−2.7+3.7 and was stronger than both olivine and the other silica polymorphs. The high stress exponent of stishovite is greater than that typically observed for power law creep, indicating it is probably (but not certainly) deforming by Peierls creep. The rheology of SiO2 minerals appears therefore to be strongly affected by the change in silicon coordination and density from fourfold in quartz and coesite to sixfold in stishovite. If the effect of Si coordination can be generalized, the increase in Si coordination (and density) associated with bridgmanite formation may explain the tenfold to 100‐fold viscosity increase around 660 km depth in the Earth.

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Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

Hunt

Whitaker

Bailey

et al. 2019

Geochem Geophys Geosyst

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“…Rocks with much higher volume fractions of silica phases would be expected to be dispersed in the lower mantle if silica exsolved from the outer core (Helffrich et al, 2018;Hirose et al, 2017). The high viscosity of stishovite prevents stishovite-bearing rocks from mixing with the surrounding mantle (Xu et al, 2017). Scattering of S waves in the lower mantle has been related to the presence of stishovite based on low S wave velocities predicted for stishovite at conditions close to the ferroelastic phase transition (Helffrich et al, 2018;Kaneshima & Helffrich, 2010).…”

Section: 1029/2018jb015835mentioning

confidence: 99%

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

et al. 2018

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High‐pressure silica polymorphs may contribute to lithologies in Earth's lower mantle. Stishovite, the tetragonal rutile‐type polymorph of SiO2, distorts to an orthorhombic CaCl2‐type structure at pressures and temperatures of the lower mantle. We compressed sintered polycrystalline stishovite and determined the unit cell parameters as a function of pressure using synchrotron X‐ray diffraction. The compression behavior of sintered polycrystalline stishovite deviates systematically from previous results on stishovite powder and single crystals. Following an initial stiffening, the bulk modulus of sintered polycrystalline stishovite drops at the ferroelastic phase transition. We analyzed the observed spontaneous strains using Landau theory to predict the complete elastic behavior of sintered polycrystalline silica across the phase transition. The reduction in bulk modulus at the phase transition as derived here from the compression curve of sintered polycrystalline silica may have implications for the seismic detection of silica‐rich materials in Earth's lower mantle.

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“…The present experiments found that MgSiO 3 bridgmanite is the liquidus phase of melts with a wider range of SiO 2 /(MgO + SiO 2 ) ratios than previously predicted by ab initio calculations and thermodynamic modeling. (Fukuda & Shimizu, 2017); while SiO 2 stishovite is more viscous than MgSiO 3 bridgmanite (Xu et al, 2017), quartz usually includes water and is thus a weak phase.…”

Section: Geophysical Implicationsmentioning

confidence: 99%

Experimental Determination of Eutectic Liquid Compositions in the MgO‐SiO₂ System to the Lowermost Mantle Pressures

Ozawa

Anzai

Hirose

et al. 2018

Geophysical Research Letters

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We have performed melting experiments on the MgO-SiO 2 binary system to 139 GPa in a diamond anvil cell. Both MgO-MgSiO 3 and MgSiO 3 -SiO 2 eutectic compositions were examined by textural/chemical characterizations of recovered samples. Results demonstrate that the MgO-MgSiO 3 eutectic becomes more enriched in MgO with increasing pressure and is close in composition to Mg 2 SiO 4 at the core-mantle boundary (CMB) pressure. On the other hand, the MgSiO 3 -SiO 2 eutectic is more SiO 2 -rich at higher pressure and exhibits SiO 2 /(MgO + SiO 2 ) = 0.66 at the CMB. These have profound implications for a large-scale compositional stratification possibly formed upon solidification of a magma ocean. The MgO-MgSiO 3 eutectic liquid being more MgO-rich than previously predicted suggests that only bridgmanite crystallizes up to 60 wt% solidification from a fully molten state of a pyrolitic lowermost mantle. In contrast, an SiO 2 layer may develop when melting/crystallization occurs in rocky objects with silica-rich enstatite-chondritic compositions.Plain Language Summary MgO-SiO 2 is the most important binary system to understand melting/crystallization processes in the Earth's crust and mantle as well as those in other rocky objects. Its melting phase relations, in particular, eutectic compositions, also have profound implications for a large-scale compositional stratification possibly formed upon solidification of a magma ocean. However, the eutectic compositions in the MgO-MgSiO 3 and MgSiO 3 -SiO 2 systems have not been examined experimentally at the deep lower mantle conditions yet. Here we performed melting experiments and determined both of these eutectic compositions to 135 GPa, corresponding to the pressure at the bottom of the mantle, by a combination of high-pressure-temperature generation in a laser-heated diamond anvil cell and textural/compositional characterization of recovered samples. The results demonstrate that the MgO-MgSiO 3 eutectic liquid is more MgO-rich than previously predicted. It suggests that a large volume of MgSiO 3 bridgmanite-dominant-layer may have formed during crystallization of a deep magma ocean and is possibly still preserved up to the present in the Earth's lower mantle. On the other hand, the MgSiO 3 -SiO 2 eutectic liquid implies that an SiO 2 -phase-rich layer could develop when extensive melting occurs in rocky objects with silica-rich enstatite-chondritic compositions.

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Silicon and oxygen self-diffusion in stishovite: Implications for stability of SiO 2 -rich seismic reflectors in the mid-mantle

Cited by 17 publications

References 38 publications

An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

Experimental Determination of Eutectic Liquid Compositions in the MgO‐SiO₂ System to the Lowermost Mantle Pressures

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Silicon and oxygen self-diffusion in stishovite: Implications for stability of SiO 2 -rich seismic reflectors in the mid-mantle

Cited by 17 publications

References 38 publications

An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite

Equation of State of Polycrystalline Stishovite Across the Tetragonal‐Orthorhombic Phase Transition

Experimental Determination of Eutectic Liquid Compositions in the MgO‐SiO2 System to the Lowermost Mantle Pressures

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Experimental Determination of Eutectic Liquid Compositions in the MgO‐SiO₂ System to the Lowermost Mantle Pressures