Viscosity of bridgmanite determined by in situ stress and strain measurements in uniaxial deformation experiments

Tsujino, Noriyoshi; Nishihara, Yu; Yoshino, Takashi; Higo, Yuji; Tange, Yoshinori

doi:10.1126/sciadv.abm1821

Cited by 16 publications

(16 citation statements)

References 52 publications

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“…Tsujino et al (2022) calculated a diffusion creep rate 50 times slower than used in our study at the same conditions. The transition from diffusion creep to dislocation creep should occur at a grain size ∼7 times larger than the size estimated byTsujino et al (2022), that is, 20-50 mm. Dislocation processes operate in parallel with diffusion creep.…”

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confidence: 69%

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

Okamoto,

Hiraga

2024

JGR Solid Earth

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In a previous study (Okamoto & Hiraga, 2022, https://doi.org/10.1029/2022jb024638), we concluded that diffusion creep and grain growth in polymineralic rocks proceed by a common diffusional mechanism. Here, we built on that finding and estimated lower mantle grain size and viscosity during a single mantle convection cycle dominated by diffusion creep. We approximated the lower mantle as a two‐phase material consisting of bridgmanite + ferropericlase and post‐perovskite + ferropericlase, depending on depth. We used previously reported self‐diffusivities for bridgmanite and post‐perovskite. We predict a bridgmanite grain‐size of tens to hundreds of microns shortly after the phase transition at ∼660 km depth. This size remains relatively constant until the mantle material enters the post‐perovskite zone, which is marked by significant grain growth up to ∼9 mm just prior to upwelling. This size is sufficient to prevent further grain growth until the mantle material reaches the top of the lower mantle. These grain sizes combined with the diffusivities yield viscosities that vary laterally and with depth. At a lateral temperature difference of up to 800 K in the lower mantle, fine‐grained cold downwelling mantle is almost as viscous as, or more likely to be softer than coarse‐grained hot upwelling mantle. The lateral viscosity variations cannot be more than 2 orders of magnitude, and we estimated viscosities of 1018–1020 Pa · s in the upper lower mantle, 5 × 1020–5 × 1022 Pa · s in the lower bridgmanite zone, and 1017–1019 Pa · s in the post‐perovskite zone, which compare well with the values estimated in previous geophysical modeling studies.

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confidence: 69%

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

Okamoto,

Hiraga

2024

JGR Solid Earth

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“…In this apparatus, two differential rams enable two opposed second‐stage anvils to deform the sample assemblage independently at constant main ram loads. This makes the deformation decoupled from pressure generation and allows us to conduct deformation experiments to large strains with well‐controlled strain rates under the steady‐state conditions (e.g., Nishihara et al., 2020; Tsujino et al., 2022).…”

Section: Discussionmentioning

confidence: 99%

Seismic Anisotropy in the Lower Mantle Transition Zone Induced by Lattice Preferred Orientation of Akimotoite

Guan

Tsujino

Tange

et al. 2022

Geophysical Research Letters

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Seismic anisotropy has been widely observed near the subducting slabs in the lower mantle transition zone (MTZ) and is often interpreted by the lattice preferred orientation (LPO) of constituent minerals. Akimotoite is one of the dominant minerals near the cold subducting slabs. Therefore, we conducted the well‐controlled uniaxial and shear deformation experiments on the MgSiO3 akimotoite aggregates at 21–23 GPa and 900–1300°C by using the D111‐type Kawai‐type multianvil apparatus. We observed strong LPOs and the most dominant slip system of akimotoite is suggested to be <10true1‾0> $< 10\overline{1}0 > $(0001). The elastic wave velocities of deformed samples were calculated to be strong azimuthal and polarization anisotropy with the velocities of horizontally polarized shear waves greater than that of vertically polarized shear waves for the horizontal mantle shearing. Our results provide important implications for the origin of observed seismic anisotropies and the mantle flow directions in the lower MTZ.

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“…D111 experiments were performed at synchrotron beamline NE7A at PF‐AR, KEK, Tsukuba, Japan (Nishihara, Tsujino, et al., 2020; Thomson et al., 2023; Tsujino et al., 2022). Throughout D111 experiments, 7M/2 assemblies were employed, denoting the (Mg,Co)O octahedral pressure medium with 7 mm edge lengths and anvils with 2 mm truncation edge lengths.…”

Section: Methodsmentioning

confidence: 99%

Rheology of Hexagonal Close‐Packed (hcp) Iron

et al. 2023

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The viscosity of hexagonal close‐packed (hcp) Fe is a fundamental property controlling the dynamics of the Earth's inner core. We studied the rheology of hcp‐Fe using high‐pressure and ‐temperature deformation experiments with in situ stress and strain measurements. Experiments were conducted using D111‐type and deformation‐DIA apparatuses at pressures of 16.3–22.6 GPa, temperatures of 423–923 K, and uniaxial strain rates of 1.52 × 10−6 to 8.81 × 10−5 s−1 in conjunction with synchrotron radiation. Experimental results showed that power‐law dislocation creep with a stress exponent of n = 4.0 ± 0.3, activation energy of E* = 240 ± 20 kJ/mol, and activation volume of V* = 1.4 ± 0.2 cm3/mol is dominant deformation mechanism at >∼800 K, whereas a mechanism with power‐law breakdown prevails at lower temperatures. An extrapolation of the power‐law dislocation creep flow law based on homologous temperature scaling suggests the viscosity of hcp‐Fe under inner core conditions is ≥∼1019 Pa s. If this power‐law dislocation creep mechanism is assumed to be the dominant mechanism in the Earth's inner core, the equatorial growth or translation mode mechanism may be the dominant geodynamical mechanism causing the observed inner core structure.

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Viscosity of bridgmanite determined by in situ stress and strain measurements in uniaxial deformation experiments

Cited by 16 publications

References 52 publications

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

A Common Diffusional Mechanism for Creep and Grain Growth in Polymineralic Rocks: Application to Lower Mantle Viscosity Estimates

Seismic Anisotropy in the Lower Mantle Transition Zone Induced by Lattice Preferred Orientation of Akimotoite

Rheology of Hexagonal Close‐Packed (hcp) Iron

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