Sound velocities in FeSi at lower mantle conditions and the origin of ultralow‐velocity zones

Abstract Carbonates play an important role in the transport and storage of carbon in the Earth’s mantle. However, the abundance of carbon and carbonates in subduction zones is still an unknown quantity. To determine the most abundant accessory phases and how they influence the dynamical processes that operate within the Earth, investigations on the vibrational, elastic, and thermodynamic properties of these phases are crucial for interpreting seismological observations. Recently, the nuclear inelastic scattering (NIS) method has proved to be a useful tool to access information on the lattice dynamics, as well as to determine Debye sound velocities of Fe-bearing materials. Here we derive the acoustic velocities from two carbonate compositions in the FeCO3-MgCO3 binary system up to ~70 GPa using the NIS method. We conclude that more Mg-rich samples, in this case (Fe0.26Mg0.74)CO3, have ~19% higher sound velocities than the pure end-member Fe composition. In addition, we observed a significant velocity increase after the Fe2+ spin transition was complete. After laser heating of FeCO3 at lower mantle conditions, we observed a dramatic velocity drop, which is probably associated with thermal decomposition to another phase. Parallel to our NIS experiments, we conducted a single-crystal X-ray diffraction (SCXRD) study to derive the equation of states of FeCO3 and (Fe0.26Mg0.74)CO3. The combined information from NIS (i.e., Debye velocities) and SCXRD (i.e., densities and bulk moduli) experiments enabled us to derive the primary and shear wave velocities of our samples. Our results are consistent with results obtained by other methods in previous studies, including Brillouin spectroscopy, inelastic X-ray scattering, and DFT calculations, supporting NIS as a reliable alternative method for studying the elastic properties of Fe-bearing systems at high pressures and temperatures. Finally, we discuss the seismic detectability of carbonates. We determine that nearly 22 wt% CO2 must be present in the subduction slab to detect a 1% shear wave velocity decrease compared to non-carbonated lithologies at the transition zone to lower mantle boundary depths.

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Correction to “Sound velocities of ferropericlase in the Earth's lower mantle”

Geophysical Research Letters ◽

10.1029/2007gl029880 ◽

2007 ◽

Vol 34 (9) ◽

Cited By ~ 5

Author(s):

Jung-Fu Lin ◽

Steven D. Jacobsen ◽

Wolfgang Sturhahn ◽

Jennifer M. Jackson ◽

Jiyong Zhao ◽

...

Keyword(s):

Lower Mantle ◽

Sound Velocities

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Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics

Geophysical Journal International ◽

10.1093/gji/ggaa495 ◽

2020 ◽

Vol 224 (2) ◽

pp. 961-972

Author(s):

A G Semple ◽

A Lenardic

Keyword(s):

Upper Mantle ◽

Lower Mantle ◽

Mantle Convection ◽

Mantle Flow ◽

Mantle Dynamics ◽

Plate Motions ◽

Low Viscosity ◽

Mantle Viscosity ◽

Flow Feature ◽

Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

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The Dupal anomaly as a trace of the upwelling lower mantle

Nature ◽

10.1038/336667a0 ◽

1988 ◽

Vol 336 (6200) ◽

pp. 667-670 ◽

Cited By ~ 144

Author(s):

Pat Castillo

Keyword(s):

Lower Mantle

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From Slater to Mott physics by epitaxially engineering electronic correlations in oxide interfaces

npj Computational Materials ◽

10.1038/s41524-021-00563-z ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Carla Lupo ◽

Evan Sheridan ◽

Edoardo Fertitta ◽

David Dubbink ◽

Chris J. Pickard ◽

...

Keyword(s):

Phase Diagram ◽

High Pressure ◽

Charge Transfer ◽

Lower Mantle ◽

Random Structure ◽

Titanium Oxides ◽

Oxide Interfaces ◽

Electronic Correlations ◽

Epitaxial Strain ◽

Magnetic Switching

AbstractUsing spin-assisted ab initio random structure searches, we explore an exhaustive quantum phase diagram of archetypal interfaced Mott insulators, i.e. lanthanum-iron and lanthanum-titanium oxides. In particular, we report that the charge transfer induced by the interfacial electronic reconstruction stabilises a high-spin ferrous Fe2+ state. We provide a pathway to control the strength of correlation in this electronic state by tuning the epitaxial strain, yielding a manifold of quantum electronic phases, i.e. Mott-Hubbard, charge transfer and Slater insulating states. Furthermore, we report that the electronic correlations are closely related to the structural oxygen octahedral rotations, whose control is able to stabilise the low-spin state of Fe2+ at low pressure previously observed only under the extreme high pressure conditions in the Earth’s lower mantle. Thus, we provide avenues for magnetic switching via THz radiations which have crucial implications for next generation of spintronics technologies.

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