Journal of Earth Science

, Volume 22, Issue 2, pp 160–168 | Cite as

Small-scale mineralogical heterogeneity from variations in phase assemblages in the transition zone and D″ layer predicted by convection modelling

  • Arie P. van den Berg
  • David A. Yuen
  • Michael H. G. Jacobs
  • Maarten V. de Hoop
Article

Abstract

Small-scale heterogeneity in the deep mantle is concentrated in the upper-mantle transition zone (TZ), in the depth range 410–660 km and also at the bottom 250 km D″ region. This encourages a more detailed investigation of the potential for seismic reflectivity imaging by modelling heterogeneous structures in mantle convection models including phase transitions of the TZ and D″ regions. We applied finite elements with variable spacing near the boundary layers in 2-D cylindrical geometry that allow for sufficient spatial resolution. We investigated several models including an extended Boussinesq (EBA) model, focused on the D″ region, and a compressible (ALA) model for the TZ region. The results for the D″ region show typical lens-shaped structures of post-perovskite (PPV) embedded in the perovskite (PV) background mantle, where the thickness of the lenses, at 200–400 km, strongly depends on the Clapeyron slope of the PV-PPV transition. A second phase transition (double crossing) occurs in case the core temperature is higher than the intercept temperature Ti. Our phase-dependent rheology results in contrasting effective viscosity between PV and PPV. Our model results reveal a distinctly clear mechanical weakening of the PPV lenses with about an order of magnitude lower viscosity. The shear wave-speed distributions computed from our convection results are strongly correlated with the heterogeneous distribution of the mineral phase. Gradients in the seismic wave-speed that are the target of seismological reflectivity imaging are clearly revealed. The wave-speed results show a clear resolution of the top and bottom interfaces of the PPV lenses. Our ALA model for the TZ is based on a thermodynamical model for the magnesium end-member of an olivine-pyroxene mantle. The model predicts a much more complex distribution of mineral phases, compared to our D″ results, in agreement with the greater number of mineral phases involved in the olivine-pyroxene phase diagram for the P, T conditions of the transition zone. Near cold downwelling flows representing subducting lithospheric slabs, where the local geotherm can differ by up to 1 000 K from the horizontal average, and small-scale lateral variations in the mineral phases can occur.

Key Words

mantle convection phase transition post-perovskite mineralogical heterogeneity 

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References Cited

  1. Ammann, M. W., Brodholt, J. P., Wookey, J., et al., 2010. First-Principles Constraints on Diffusion in Lower-Mantle Minerals and a Weak D″ Layer. Nature, 465(7297): 462–465CrossRefGoogle Scholar
  2. Boehler, R., 2000. High-Pressure Experiments and the Phase Diagram of Lower Mantle and Core Materials. Reviews of Geophysics, 38(2): 221–245CrossRefGoogle Scholar
  3. Cadek, O. Fleitout, L., 2006. Effect of Lateral Viscosity Variations in the Core-Mantle Boundary Region on Predictions of the Long-Wavelength Geoid. Stud. Geophys. Geod., 50(2): 217–232CrossRefGoogle Scholar
  4. Cao, Q., Wang, P., van der Hilst, R. D., et al., 2010. Imaging the Upper Mantle Transition Zone with a Generalized Radon Transform of SS Precursors. Phys. Earth Planet. Inter., 180(1–2): 80–91CrossRefGoogle Scholar
  5. Catalli, K., Shim, S. H., Prakapenka, V., 2009. Thickness and Claeyron Slope of the Post-Perovskite Boundary. Nature, 462(7274): 782–785CrossRefGoogle Scholar
  6. Christensen, A. U. R., Yuen, D. A., 1985. Layered Convection Induced by Phase Transitions. J. Geophys. Res., 90:10291–10300CrossRefGoogle Scholar
  7. Connolly, J. A. D., 2005. Computation of Phase Equilibria by Linear Programming: A Tool for Geodynamic Modeling and Its Application to Subduction Zone Decarbonation. Earth Planet. Sci. Lett., 236(1–2): 524–541CrossRefGoogle Scholar
  8. Daessler, R., Yuen, D. A., 1993. The Effects of Phase Transition Kinetics on Subducting Slabs. Geophys. Res. Lett., 20(23): 2603–2606CrossRefGoogle Scholar
  9. de Hoop, M. V., Smith, H., Uhlmann, G., et al., 2009. Seismic Imaging with the Generalized Radon Transform: A Curvelet Transform Perspective. Inverse Problems, 25(2): 025005CrossRefGoogle Scholar
  10. Hernlund, J. W., Thomas, C., Tackley, P. J., 2005. A Doubling of the Post-Perovskite Phase Boundary and Structure of the Earth’s Lowermost Mantle. Nature, 434(7035): 882–886CrossRefGoogle Scholar
  11. Hunt, S. A., Weidner, D. J., Li, L., et al., 2009. Weakening of Calcium Iridate during Its Transformation from Perovskite to Post-Perovskite. Nature Geoscience, 2(11):794–797CrossRefGoogle Scholar
  12. Jacobs, M. H. G., de Jong, B. H. W. S., 2007. Placing Constraints on Phase Equilibria and Thermophysical Properties in the System MgO-SiO2 by a Thermodynamically Consistent Vibrational Method. Geochimica et Cosmochimica Acta, 71(14): 3630–3655CrossRefGoogle Scholar
  13. Jacobs, M. H. G., van den Berg, A. P., 2011. Complex Phase Distribution and Seismic Velocity Structure of the Transition Zone: Convection Model Predictions for a Magnesium-Endmember Olivine-Pyroxene Mantle. Phys. Earth Planet. Inter. (Accepted)Google Scholar
  14. Jarvis, G. T., McKenzie, D. P., 1980. Convection in a Compressible Fluid with Infinite Prandtl Number. J. Fluid Mech., 96: 515–583CrossRefGoogle Scholar
  15. Karato, S. I., 2008. Deformation of Earth Materials: An Introduction to the Rheology of Solid Earth. Cambridge University Press, CambridgeGoogle Scholar
  16. Karato, S. I., 2010. The Influence of Anisotropic Diffusion on the High-Temperature Creep of a Polycrystalline Aggregate. Phys. Earth Planet. Inter., 183(3–4): 468–472CrossRefGoogle Scholar
  17. King, S. D., Lee, C., van Keken, P. E., et al., 2010. A Community Benchmark for 2-D Cartesian Compressible Convection in the Earth’s Mantle. Geophys. J. Int., 180(1): 73–87CrossRefGoogle Scholar
  18. Lay, T., Hernlund, J., Garnero, E. J., et al., 2006. A Post-Perovskite Lens and D″ Heat Flux beneath the Central Pacific. Science, 314(5803): 1272–1276CrossRefGoogle Scholar
  19. Murakami, M., Hirose, K., Kawamura, K., et al., 2004. Post-Perovskite Phase Transition in MgSiO3. Science, 304(5672): 855–858CrossRefGoogle Scholar
  20. Nakagawa, T., Tackley, P. J., 2010. Influence of Initial CMB Temperature and Other Parameters on the Thermal Evolution of Earth’s Core Resulting from Thermochemical Spherical Mantle Convection. Geochemistry, Geophysics, Geosystems, 11: Q06001CrossRefGoogle Scholar
  21. Schubert, G., Turcotte, D. L., Olson, P., 2001. Mantle Convection in the Earth and Planets. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  22. Steinbach, V., Hansen, U., Ebel, A., 1989. Compressible Convection in the Earth’s Mantle: A Comparison of Different Approaches. Geophys. Res. Lett., 16: 633–636CrossRefGoogle Scholar
  23. Tosi, N., Cadek, O., Martinec, Z., et al., 2009. Is the Long-Wavelength Geoid Sensitive to the Presence of Post-Perovskite above the Core-Mantle Boundary? Geophys. Res. Lett., 36: L05303CrossRefGoogle Scholar
  24. Vacher, P., Spakman, W., Wortel, M. J. R., 1999. Numerical Tests on the Seismic Visibility of Metastable Minerals in Subduction Zones. Earth Planet. Sci. Lett., 170(3):335–349CrossRefGoogle Scholar
  25. van den Berg, A. P., van Keken, P. E., Yuen, D. A., 1993. The Effects of a Composite Non-Newtonian and Newtonian Rheology on Mantle Convection. Geophysical Journal International, 115(1): 62–78CrossRefGoogle Scholar
  26. van den Berg, A. P., de Hoop, M. V., Yuen, D. A., et al., 2010. Geodynamical Modeling and Multiscale Seismic Expression of Thermo-chemical Heterogeneity and Phase Transitions in the Lowermost Mantle. Phys. Earth Planet. Int., 180(3–4): 244–257CrossRefGoogle Scholar
  27. van der Hilst, R. D., de Hoop, M. V., Wang, P., et al., 2007. Seismostratigraphy and Thermal Structure of Earth’s Core-Mantle Boundary Region. Science, 315(5820):1813–1817CrossRefGoogle Scholar
  28. van Hunen, J., van den Berg, A. P., Vlaar, N. J., 2002. On the Role of Subducting Oceanic Plateaus in the Development of Shallow Flat Subduction. Tectonophysics, 352(3–4):317–33CrossRefGoogle Scholar

Copyright information

© China University of Geosciences and Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • Arie P. van den Berg
    • 1
  • David A. Yuen
    • 2
  • Michael H. G. Jacobs
    • 3
  • Maarten V. de Hoop
    • 4
  1. 1.Earth Sciences DepartmentUtrecht UniversityUtrechtThe Netherlands
  2. 2.Department of Geology and Geophysics and Minnesota Supercomputing InstituteUniversity of MinnesotaMinneapolisUSA
  3. 3.Institut für MetallurgieTU ClausthalClausthal-ZellerfeldGermany
  4. 4.Department of Mathematics and Center of Applied and Computational MathematicsPurdue UniversityWest LafayetteUSA

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