The influences of composition-sand temperature-dependent rheology in thermal-chemical convection on entrainment of the D"-layer

B. Schott, D. A. Yuen, A. Braun

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16 Scopus citations


The entrainment dynamics in the D″-layer are influenced by multitudinous factors, such as thermal and compositional buoyancy, and temperature- and composition-dependent viscosity. Here, we are focusing on the effect of compositionally dependent viscosity on the mixing dynamics of the D″-layer, arising from the less viscous but denser D″-material. The marker method, with one million markers, is used for portraying the fine scale features of the compositional components, D″-layer and lower-mantle. The D″-layer has a higher density but a lower viscosity than the ambient lower-mantle, as suggested by melting point systematics. Results from a two-dimensional finite-difference numerical model including the extended Boussinesq approximation with dissipation number Di = 0.3, show that a D″-layer, less viscous than the ambient mantle by 1.5 orders of magnitude, cannot efficiently mix with the lower-mantle, even though the buoyancy parameter is as low as Rp = 0.6. However, very small-scale schlieren structures of D″-layer material are entrained into the lower-mantle. These small-scale lower-mantle heterogeneities have been imaged with one-dimensional wavelets in order to delineate quantitatively the multiscale features. They may offer an explanation for small-scale seismic heterogeneity inferred by seismic scattering in the lower-mantle.

Original languageEnglish (US)
Pages (from-to)43-65
Number of pages23
JournalPhysics of the Earth and Planetary Interiors
Issue number1-2
StatePublished - 2002

Bibliographical note

Funding Information:
We thank discussions with U. Christensen, U. Hansen, S.-Karato, H. Paulssen, P. Tackley, W. Wang, and D. Yamazaki, and particularly H. Schmeling and an anonymous reviewer for their excellent reviews, that helped us improving the manuscript. Special thanks to H. Schmeling for kindly providing his code FDCON, and to Swedish NFR for supporting Bertram Schott with a Post-Doc stipend, which made this research possible. Support for this research also comes from the geophysics program of NSF. All calculations have been done on the SGI-Origin2000 computers of the Minnesota Supercomputing Institute (MSI).

Copyright 2017 Elsevier B.V., All rights reserved.


  • D"-layer
  • Entrainment
  • Seismic scattering
  • Thermochemical convection


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