The thermal boundary-layer interpretation of D″ and its role as a plume source

doi:10.1016/0031-9201(83)90006-7

Physics of the Earth and Planetary Interiors

Volume 33, Issue 1, August 1983, Pages 45-55

https://doi.org/10.1016/0031-9201(83)90006-7 Get rights and content

Abstract

The “anomalous” layer in the lowermost mantle, identified as D″ in the notation of K.E. Bullen, appears in the PREM Earth model as a 150 km-thick zone in which the gradient of incompressibility with pressure, $d K d P$ , is almost 1.6, instead of 3.2 as in the overlying mantle. Since PREM shows no accompanying change in density or density gradient, we identify D″ as a thermal boundary layer and not as a chemically distinct zone. The anomaly in $d K d P$ is related to the temperature gradient by the temperature dependence of K_s, for which we present a thermodynamic identity in terms of accessible quantities. This gives the numerical result (∂K_s/∂T)_P=−1.6×10⁷ Pa K⁻¹ for D″ material. The corresponding temperature increment over the D″ range is 840 K. Such a layer cannot be a static feature, but must be maintained by a downward motion of the lower mantle toward the core-mantle boundary with a strong horizontal flow near the base of D″. Assuming a core heat flux of 1.6 × 10¹² W, the downward speed is 0.07 mm y⁻¹ and the temperature profile in D″, scaled to match PREM data, is approximately exponential with a scale height of 73 km. The inferred thermal conductivity is 1.2 W m⁻¹ K⁻¹. Using these values we develop a new analytical model of D″ which is dynamically and thermally consistent. In this model, the lower-mantle material is heated and softened as it moves down into D″ where the strong temperature dependence of viscosity concentrates the horizontal flow in a layer ∼ 12 km thick and similarly ensures its removal via narrow plumes.

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The thermal boundary-layer interpretation of D″ and its role as a plume source

Abstract

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Solid State Phys.

Geochim. Cosmochim. Acta

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

The Hildebrand equation of state applied to minerals relevant to geophysics

Phys. Chem. Minerals

Temperature profiles in the Earth

Structure of the F layer and reasons for convection in the Earth's core

Doklady Akad. Nauk S.S.S.R.

A thermodynamically based equation of state for the lower mantle

J. Geophys. Res.

Thermodynamic parameters in the Earth as determined from seismic profiles

Geophys. J. R. Astron. Soc.

An Earth model based on a compressibility-pressure hypothesis

Mon. Not. R. Astron. Soc. Geophys.

On seismic-wave scattering by a rough core-mantle boundary

Geophys. J. R. Astron. Soc.

P and S waves diffracted around the core and the velocity structure at the base of the mantle

Geophys. J. R. Astron. Soc.