Skip to main content

Advertisement

Earth, Planets and Space
Earth, Planets and Space Cover Image
We’d like to understand how you use our websites in order to improve them. Register your interest.
Download PDF

Mantle-driven geodynamo features—effects of post-Perovskite phase transition

Earth, Planets and Space volume 61, pages1255–1268(2009)Cite this article

Abstract

Exploring the impact of the heterogeneous lower mantle on the geodynamo requires knowledge of the heat flux anomaly across the core-mantle boundary. Most studies so far used a purely thermal interpretation of seismic shear wave anomalies to assign heterogeneous heat flux boundary conditions on numerical dynamo models, ignoring phase transition or compositional origins. A recent study of mantle convection (Nakagawa and Tackley, 2008) provides guidelines to include such non-thermal effects. Here we construct maps of heat flux across the core-mantle boundary based on a lower mantle tomography model (Masters et al, 2000) with a combined thermal and post-Perovskite phase transition interpretation. We impose these patterns as outer boundary conditions on numerical dynamo simulations and study the impact of accounting for post-Perovskite effects on the long-term time-average properties of the dynamo. We then compare our results with geophysical observations. We find in all cases that surface downwellings associated with cyclones concentrate intense non-axisymmetric magnetic flux at high-latitudes, the surface flow contains a large anticlockwise vortex at mid-latitudes of the southern hemisphere, and the inner boundary buoyancy flux is dominated by a Y 02 pattern. Boundary-driven time-average surface flow with some equatorial asymmetry is organized in the shell by quasi-axial convective rolls that extract more buoyancy from low-latitudes of the inner-boundary. These positive inner boundary buoyancy flux structures are found at low-latitudes of the northern hemisphere, in some places due to cyclonic flow at mid-latitudes of the southern hemisphere connecting with higher latitude cyclonic flow in the northern hemisphere. Accounting for post-Perovskite effects improves the recovery of several geodynamo observations, including the Atlantic/Pacific hemispherical dichotomy in core flow activity, the single intense paleomagnetic field structure in the southern hemisphere, and possibly the m = 1 dominant mode of inner-core seismic heterogeneity.

References

  1. Amit, H. and U. Christensen, Accounting for magnetic diffusion in core flow inversions from geomagnetic secular variation, Geophys. J. Int., 175, 913–924, 2008.

    Article  Google Scholar 

  2. Amit, H. and P. Olson, Helical core flow from geomagnetic secular variation, Phys. Earth Planet. Inter., 147, 1–25, 2004.

    Article  Google Scholar 

  3. Amit, H. and P. Olson, Time-average and time-dependent parts of core flow, Phys. Earth Planet. Inter., 155, 120–139, 2006.

    Article  Google Scholar 

  4. Amit, H., J. Aubert, G. Hulot, and P. Olson, A simple model for mantle-driven flow at the top of Earth’s core, Earth Planets Space, 60, 845–854, 2008.

    Article  Google Scholar 

  5. Aubert, J., H. Amit, and G. Hulot, Detecting thermal boundary control in surface flows from numerical dynamos, Phys. Earth Planet. Inter., 160, 143–156, 2007.

    Article  Google Scholar 

  6. Aubert, J., H. Amit, G. Hulot, and P. Olson, Thermo-chemical flows couple Earth’s inner core growth to mantle heterogeneity, Nature, 454, 758–761, 2008.

    Article  Google Scholar 

  7. Bloxham, J., Time-independent and time-dependent behaviour of high-latitude flux bundles at the core-mantle boundary, Geophys. Res. Lett., 29, doi:10.1029/2001gl014543, 2002.

  8. Bloxham, J. and D. Gubbins, Thermal core-mantle interactions, Nature, 325, 511–513, 1987.

    Article  Google Scholar 

  9. Busse, F., A model of the geodynamo, Geophys. J. R. Astron. Soc., 42, 437–459, 1975.

    Article  Google Scholar 

  10. Carlut, J. and V. Courtillot, How complex is the time-averaged geomagnetic field over the last 5 million years?, Geophys. J. Int., 134, 527–544, 1998.

    Article  Google Scholar 

  11. Christensen, U. and P. Olson, Secular variation in numerical geodynamo models with lateral variations of boundary heat flow, Phys. Earth Planet. Inter., 138, 39–54, 2003.

    Article  Google Scholar 

  12. Constable, C., Non-dipole field, in Encyclopedia of Geomagnetism and Paleomagnetism, edited by Gubbins, D. and E. Herrera-Bervera, 1054 pp, Springer, The Netherlands, 2007.

    Google Scholar 

  13. Creager, K., Anisotropy of the inner core from differential travel-times of the phases PKP and PKIKP, Nature, 356, 309–314, 1992.

    Article  Google Scholar 

  14. Deschamps, F., J. Trampert, and P. Tackley, Thermo-chemical structure of the lower mantle: seismological evidence and consequences for geody-namics, in Superplume: Beyond Plate Tectonics, edited by Yuen, D., S. Maruyama, S. Karato, and B. Windely, 568 pp, Springer, The Netherlands, 2007.

    Google Scholar 

  15. Glatzmaier, G., R. Coe, L. Hongre, and P. Roberts, The role of the Earth’s mantle in controlling the frequency of geomagnetic reversals, Nature, 401, 885–890, 1999.

    Article  Google Scholar 

  16. Gubbins, D. and S. Gibbons, Low Pacific secular variation, in Timescales of the paleomagnetic field, edited by Channell, J., D. Kent, W. Lowrie, and J. Meert, 320 pp, Geophysical monograph series Vol. 145, Washington D.C., 2004.

    Google Scholar 

  17. Gubbins, D., A. Willis, and B. Sreenivasan, Correlation of Earth’s magnetic field with lower mantle thermal and seismic structure, Phys. Earth Planet. Inter., 162, 256–260, 2007.

    Article  Google Scholar 

  18. Holme, R., Large-scale flow in the core, in Treatise on Geophysics Vol. 8, edited by Olson, P., 376 pp, Elsevier Science, London, 2007.

    Google Scholar 

  19. Hulot, G., C. Eymin, B. Langlais, M. Mandea, and N. Olsen, Small-scale structure of the geodynamo inferred from Oersted and Magsat satellite data, Nature, 416, 620–623, 2002.

    Article  Google Scholar 

  20. Iitaka, T., K. Hirose, K. Kawamura, and M. Murakami, The elasticity of the MgSiO3 post-Perovskite phase in the Earth’s lowermost mantle, Nature, 430, 442–445, 2004.

    Article  Google Scholar 

  21. Jackson, A., Time-dependency of tangentially geostrophic core surface motions, Phys. Earth Planet. Inter., 103, 293–311, 1997.

    Article  Google Scholar 

  22. Jackson, A., A. Jonkers, and M. Walker, Four centuries of geomagnetic secular variation from historical records, Phil. Trans. R. Soc. Lond., A358, 957–990, 2000.

    Article  Google Scholar 

  23. Kelly, P. and D. Gubbins, The geomagnetic field over the past 5 million years, Geophys. J. Int., 128, 315–330, 1997.

    Article  Google Scholar 

  24. Labrosse, S., J.-W. Hernlund, and N. Coltice, A crystallizing dense magma ocean at the base of the Earth’s mantle, Nature, 450, 866–869, 2007.

    Article  Google Scholar 

  25. Lay, T., E.-J. Garnero, and Q. Williams, Partial melting in a thermo-chemical boundary layer at the base of the mantle, Phys. Earth Planet. Inter, 146, 441–467, 2004.

    Article  Google Scholar 

  26. Lay, T., J. Hernlund, E. Garnero, and M. Thorne, A post-Perovskite lens and D″ heat flux beneath the central Pacific, Science, 314, 1272–1276, 2006.

    Article  Google Scholar 

  27. Le Bars, M. and A. Davaille, Whole layer convection in a heterogeneous planetary mantle, J. Geophys. Res., 109, Bo3403, 2004.

    Article  Google Scholar 

  28. Masters, G., S. Johnson, G. Laske, and H. Bolton, A shear-velocity model of the mantle, Philos.Trans. R. Soc. Lond. Ser., A354, 1385–1411, 1996.

    Article  Google Scholar 

  29. Masters, G., G. Laske, H. Bolton, and A. Dziewonski, The relative behavior of shear velocity, bulk sound velocity, and compressional velocity in the mantle: Implications for chemical and thermal structure, in Earth’s deep interior, edited by Karato, S., A. Forte, R. Liebermann, G. Masters, and L. Stixrude, 297 pp, AGU monograph Vol. 117, Washington D.C., 2000.

    Google Scholar 

  30. Matsumoto, N., A. Namiki, and I. Sumita, influence of a basal thermal anomaly on mantle convection, Phys. Earth Planet. Inter., 157, 208–222, 2006.

    Article  Google Scholar 

  31. Morelli, A., A. Dziewonski, and J. Woodhouse, Anisotropy of the inner core inferred from PKIKP travel-times, Geophys. Res. Lett., 13, 1545–1548, 1986.

    Article  Google Scholar 

  32. Murakami, M., K. Hirose, N. Sata, Y. Ohishi, and K. Kawamura, Post-Perovskite phase transition in MgSiO3, Science, 304, 855–858, 2004.

    Article  Google Scholar 

  33. Murakami, M., S. Sinogeikin, J. Bass, and J. Li, Sound velocity of MgSiO3 Perovskite to mbar pressure, Earth Planet. Sci. Lett., 256, 47–54, 2007.

    Article  Google Scholar 

  34. Nakagawa, T. and P. Tackley, Lateral variations in CMB heat flux and deep mantle seismic velocity caused by a thermal-chemical-phase boundary layer in 3D spherical convection, Earth Planet. Sci. Lett., 271, 348–358, 2008.

    Article  Google Scholar 

  35. Ni, S., E. Tan, M. Gurnis, and D. Helmberger, Sharp sides to the African super plume, Science, 296, 1850–1852, 2002.

    Article  Google Scholar 

  36. Niu, F. and L. Wen, Hemispherical variations in seismic velocity at the top of the Earth’s inner core, Nature, 410, 1081–1084, 2001.

    Article  Google Scholar 

  37. Oganov, A. and S. Ono, Theoretical and experimental evidence for a post-Perovskite phase of MgSiO3 in Earth’s D″ layer, Nature, 430, 445–448, 2004.

    Article  Google Scholar 

  38. Olson, P. and U. Christensen, The time averaged magnetic field in numerical dynamos with nonuniform boundary heat flow, Geophys. J. Int., 151, 809–823, 2002.

    Article  Google Scholar 

  39. Olson, P., U. Christensen, and G. Glatzmaier, Numerical modeling of the geodynamo: Mechanisms of field generation and equilibration, J. Geophys. Res., 104, 10383–10404, 1999.

    Article  Google Scholar 

  40. Olson, P., P. Driscoll, and H. Amit, Dipole collapse and reversal precursors in a numerical dynamo, Phys. Earth Planet. Inter., 173, 121–140, 2009.

    Article  Google Scholar 

  41. Ritsema, J., A. McNamara, and A. Bull, Tomographics filtering of geo-dynamic models: implications for model interpretation and large-scale mantle structure, J. Geophys. Res., 112, doi:10.1029/2005GL023887, 2007.

  42. Song, X. and D. Helmberger, Anisotropy of Earth’s inner-core, Geophys. Res. Lett., 20, 2591–2594, 1993.

    Article  Google Scholar 

  43. Stackhouse, S., J. Brodholt, and G. Price, Elastic anisotropy of FeSiO3 end-member of the Perovskite and post-Perovskite phase, Geophys. Res. Lett., 33, L01304, doi:10.1029/2005GL023887, 2006.

    Article  Google Scholar 

  44. Su, W.-J. and A. Dziewonski, Simultaneous inversion for 3-D variations in shear and bulk velocity in the mantle, Phys. Earth Planet. Inter., 100, 135–156, 1997.

    Article  Google Scholar 

  45. Su, W.-J., R. Woodward, and A. Dziewonski, Degree-12 model of shear velocity heterogeneity in the mantle, J. Geophys. Res., 99, 6945–6980, 1994.

    Article  Google Scholar 

  46. Tackley, P., Strong heterogeneity caused by deep mantle layering, Geochem. Geophys. Geosyst., 3, 1024, 2002.

    Article  Google Scholar 

  47. Takahashi, F., M. Matsushima, and Y. Honkura, Scale variability in convection-driven MHD dynamos at low Ekman number, Phys. Earth Planet. Inter, 167, 168–178, 2008a.

    Article  Google Scholar 

  48. Takahashi, F, H. Tsunakawa, M. Matsushima, N. Mochizuki, and Y Honkura, Effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength, Earth Planet. Sci. Lett., 272, 738–746, 2008b.

    Article  Google Scholar 

  49. Tanaka, S. and H. Hamaguchi, Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC)-PKP(DF) times, J. Geophys. Res., 102, 2925–2938, 1997.

    Article  Google Scholar 

  50. Thurber, C. and J. Ritsema, Theory and observations—seismic tomography and inverse methods, in Treatise on Geophysics. Vol. 1, edited by Romanowicz, B. and A. Dziewonski, 872 pp, Elsevier Science, London, 2007.

    Google Scholar 

  51. To, A., B. Romanowicz, Y. Capdeville, and N. Takeuchi, 3D effects of sharp boundaries at the borders of the African and Pacific superplumes: observation and modeling, Earth Planet. Sci. Lett., 233, 137–153, 2005.

    Article  Google Scholar 

  52. Tsuchiya, T. and J. Tsuchiya, Effect of impurity on the elasticity of Perovskite and post-Perovskite: Velocity contrast across the post-Perovskite transition in (Mg,Fe,Al)(Si,Al)O3, Geophys. Res. Lett., 33, L12S04, 2006.

    Article  Google Scholar 

  53. Wentzcovitch, R., T. Tsuchiya, and J. Tsuchiya, MgSiO3 post-Perovskite at D″ conditions, Proc. Nat. Acad. Sci., 103, 543–546, 2006.

    Article  Google Scholar 

  54. Wicht, J., Inner-core conductivity in numerical dynamo simulations, Phys. Earth Planet. Inter., 132, 281–302, 2002.

    Article  Google Scholar 

  55. Williams, Q. and E.-J. Garnero, Seismic evidence for partial melt at the base of Earth’s mantle, Science, 273, 1528–1530, 1998.

    Article  Google Scholar 

  56. Williams, Q., J. Revenaugh, and E.-J. Garnero, A correlation between ultra-low basal velocities in the mantle and hot spots, Science, 281, 546–549, 1996.

    Article  Google Scholar 

  57. Willis, A., B. Sreenivasan, and D. Gubbins, Thermal core-mantle interaction: exploring regimes for locked dynamo action, Phys. Earth Planet. Inter., 165, 83–92, 2007.

    Article  Google Scholar 

  58. Wookey, J., S. Stackhouse, J.-M. Kendall, J. Brodholt, and G. Price, Efficacy of the post-Perovskite phase as an explanation for lowermost mantle seismic properties, Nature, 438, 1004–1007, 2005.

    Article  Google Scholar 

  59. Yoshida, S., I. Sumita, and M. Kumazawa, Growth model of the inner core coupled with the outer core dynamics and the resulting elastic anisotropy, J. Geophys. Res., 101, 28085–28103, 1996.

    Article  Google Scholar 

Download references

Author information

Affiliations

  1. Laboratoire de Planétologie et de Géodynamique, CNRS, Université de Nantes, Nantes Atlantique Universités, UMR CNRS 6112, 2 rue de la Houssinière, F-44000, Nantes, France
    • Hagay Amit
    •  & Gaël Choblet
Authors
  1. Hagay Amit
    View author publications
    You can also search for this author in
  2. Gaël Choblet
    View author publications
    You can also search for this author in

Corresponding author

Correspondence to Hagay Amit.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Amit, H., Choblet, G. Mantle-driven geodynamo features—effects of post-Perovskite phase transition. Earth Planet Sp 61, 1255–1268 (2009). https://doi.org/10.1186/BF03352978

Download citation

Key words

  • Geodynamo
  • mantle tomography
  • post-Perovskite
  • geomagnetic field
  • core flow
  • inner core