- Open Access
Mantle-driven geodynamo features—effects of post-Perovskite phase transition
Earth, Planets and Space volume 61, pages1255–1268(2009)
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.
Amit, H. and U. Christensen, Accounting for magnetic diffusion in core flow inversions from geomagnetic secular variation, Geophys. J. Int., 175, 913–924, 2008.
Amit, H. and P. Olson, Helical core flow from geomagnetic secular variation, Phys. Earth Planet. Inter., 147, 1–25, 2004.
Amit, H. and P. Olson, Time-average and time-dependent parts of core flow, Phys. Earth Planet. Inter., 155, 120–139, 2006.
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.
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.
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.
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.
Bloxham, J. and D. Gubbins, Thermal core-mantle interactions, Nature, 325, 511–513, 1987.
Busse, F., A model of the geodynamo, Geophys. J. R. Astron. Soc., 42, 437–459, 1975.
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.
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.
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.
Creager, K., Anisotropy of the inner core from differential travel-times of the phases PKP and PKIKP, Nature, 356, 309–314, 1992.
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.
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.
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.
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.
Holme, R., Large-scale flow in the core, in Treatise on Geophysics Vol. 8, edited by Olson, P., 376 pp, Elsevier Science, London, 2007.
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.
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.
Jackson, A., Time-dependency of tangentially geostrophic core surface motions, Phys. Earth Planet. Inter., 103, 293–311, 1997.
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.
Kelly, P. and D. Gubbins, The geomagnetic field over the past 5 million years, Geophys. J. Int., 128, 315–330, 1997.
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.
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.
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.
Le Bars, M. and A. Davaille, Whole layer convection in a heterogeneous planetary mantle, J. Geophys. Res., 109, Bo3403, 2004.
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.
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.
Matsumoto, N., A. Namiki, and I. Sumita, influence of a basal thermal anomaly on mantle convection, Phys. Earth Planet. Inter., 157, 208–222, 2006.
Morelli, A., A. Dziewonski, and J. Woodhouse, Anisotropy of the inner core inferred from PKIKP travel-times, Geophys. Res. Lett., 13, 1545–1548, 1986.
Murakami, M., K. Hirose, N. Sata, Y. Ohishi, and K. Kawamura, Post-Perovskite phase transition in MgSiO3, Science, 304, 855–858, 2004.
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.
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.
Ni, S., E. Tan, M. Gurnis, and D. Helmberger, Sharp sides to the African super plume, Science, 296, 1850–1852, 2002.
Niu, F. and L. Wen, Hemispherical variations in seismic velocity at the top of the Earth’s inner core, Nature, 410, 1081–1084, 2001.
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.
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.
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.
Olson, P., P. Driscoll, and H. Amit, Dipole collapse and reversal precursors in a numerical dynamo, Phys. Earth Planet. Inter., 173, 121–140, 2009.
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.
Song, X. and D. Helmberger, Anisotropy of Earth’s inner-core, Geophys. Res. Lett., 20, 2591–2594, 1993.
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.
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.
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.
Tackley, P., Strong heterogeneity caused by deep mantle layering, Geochem. Geophys. Geosyst., 3, 1024, 2002.
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.
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.
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.
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.
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.
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.
Wentzcovitch, R., T. Tsuchiya, and J. Tsuchiya, MgSiO3 post-Perovskite at D″ conditions, Proc. Nat. Acad. Sci., 103, 543–546, 2006.
Wicht, J., Inner-core conductivity in numerical dynamo simulations, Phys. Earth Planet. Inter., 132, 281–302, 2002.
Williams, Q. and E.-J. Garnero, Seismic evidence for partial melt at the base of Earth’s mantle, Science, 273, 1528–1530, 1998.
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.
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.
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.
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.
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
- mantle tomography
- geomagnetic field
- core flow
- inner core