Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Review Article
  • Published:

Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle

Nature Geoscience volume 9, pages 481–489 (2016)Cite this article

Subjects

Abstract

Seismic images of Earth's interior reveal two massive anomalous zones at the base of the mantle, above the core, where seismic waves travel slowly. The mantle materials that surround these anomalous regions are thought to be composed of cooler rocks associated with downward advection of former oceanic tectonic plates. However, the origin and composition of the anomalous provinces is uncertain. These zones have long been depicted as warmer-than-average mantle materials related to convective upwelling. Yet, they may also be chemically distinct from the surrounding mantle, and potentially partly composed of subducted or primordial material, and have therefore been termed thermochemical piles. From seismic, geochemical and mineral physics data, the emerging view is that these thermochemical piles appear denser than the surrounding mantle materials, are dynamically stable and long-lived, and are shaped by larger-scale mantle flow. Whether remnants of a primordial layer or later accumulations of more-dense materials, the composition of the piles is modified over time by stirring and by chemical reactions with material from the surrounding mantle, underlying core and potentially from volatile elements transported into the deep Earth by subducted plates. Upwelling mantle plumes may originate from the thermochemical piles, so the unusual chemical composition of the piles could be the source of distinct trace-element signatures observed in hotspot lavas.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Large low shear velocity provinces (LLSVPs) with other phenomena.
Figure 2: LLSVP observations and interpretations.
Figure 3: Thermochemical pile evolution.
Figure 4: Chemical composition and mineralogy of pyrolite versus mid-ocean ridge basalt (MORB).

Similar content being viewed by others

References

  1. Ritsema, J., Deuss, A., van Heijst, H. J. & Woodhouse, J. H. S40RTS: a degree-40 shear-velocity model for the mantle from new Rayleigh wave dispersion, teleseismic traveltime and normal-mode splitting function measurements. Geophys. J. Int. 184, 1223–1236 (2011).

    Article  Google Scholar 

  2. Lekic, V., Cottaar, S., Dziewonski, A. & Romanowicz, B. Cluster analysis of global lower mantle tomography: a new class of structure and implications for chemical heterogeneity. Earth Planet. Sci. Lett. 357, 68–77 (2012).

    Article  Google Scholar 

  3. Garnero, E. J. & McNamara, A. K. Structure and dynamics of Earth's lower mantle. Science 320, 626–628 (2008).

    Article  Google Scholar 

  4. Koelemeijer, P., Ritsema, J., Deuss, A. & van Heijst, H. J. SP12RTS: a degree-12 model of shear- and compressional-wave velocity for Earth's mantle. Geophys. J. Int. 204, 1024–1036 (2016).

    Article  Google Scholar 

  5. He, Y. & Wen, L. Geographic boundary of the “Pacific Anomaly” and its geometry and transitional structure in the north. J. Geophys. Res. 117, B09308 (2012).

    Article  Google Scholar 

  6. Tanaka, S. et al. On the vertical extent of the large low shear velocity province beneath the South Pacific Superswell. Geophys. Res. Lett. 36, L07305 (2009).

    Google Scholar 

  7. Suetsugu, D. et al. South Pacific mantle plumes imaged by seismic observation on islands and seafloor. Geochem. Geophys. Geosyst. 10, Q11014 (2009).

    Article  Google Scholar 

  8. French, S. W. & Romanowicz, B. Broad plumes rooted at the base of the Earth's mantle beneath major hotspots. Nature 525, 95–99 (2015).

    Article  Google Scholar 

  9. Zhao, C., Garnero, E. J., McNamara, A. K., Schmerr, N. & Carlson, R. W. Seismic evidence for a chemically distinct thermochemical reservoir in Earth's deep mantle beneath Hawaii. Earth Planet. Sci. Lett. 426, 143–153 (2015).

    Article  Google Scholar 

  10. Sun, D. & Miller, M. S. Study of the western edge of the African large low shear velocity province. Geochem. Geophys. Geosyst. 14, 3109–3125 (2013).

    Article  Google Scholar 

  11. Frost, D. A. & Rost, S. The P-wave boundary of the large-low shear velocity province beneath the Pacific. Earth Planet. Sci. Lett. 403, 380–392 (2014).

    Article  Google Scholar 

  12. McNamara, A. K., Garnero, E. J. & Rost, S. Tracking deep mantle reservoirs with ultra low velocity zones. Earth Planet. Sci. Lett. 299, 1–9 (2010).

    Article  Google Scholar 

  13. Rost, S., Earle, P. S., Shearer, P. M., Frost, D. A. & Selby, N. D. in The Earth's Heterogeneous Mantle: A Geophysical, Geodynamical, and Geochemical Perspective (eds Khan, A. & Deschamps, F.) 367–390 (Springer Publishing, 2015).

    Google Scholar 

  14. Frost, D. A., Rost, S., Selby, N. D. & Stuart, G. W. Detection of a tall ridge at the core–mantle boundary from scattered PKP energy. Geophys. J. Int. 195, 558–574 (2013).

    Article  Google Scholar 

  15. Cobden, L. & Thomas, C. The origin of D" reflections: a systematic study of seismic array data sets. Geophys. J. Int. 194, 1091–1118 (2013).

    Article  Google Scholar 

  16. Cobden, L., Thomas, C. & Trampert, J. The Earth's Heterogeneous Mantle: A Geophysical, Geodynamical, and Geochemical Perspective (eds Khan, A. & Deschamps, F.) 391–440 (Springer Publishing, 2015).

    Google Scholar 

  17. Nakagawa, T. & Tackley, P. J. Effects of low-viscosity post-perovskite on thermo-chemical mantle convection in a 3-D spherical shell. Geophys. Res. Lett. 38, L04309 (2011).

    Article  Google Scholar 

  18. Lay, T., Hernlund, J., Garnero, E. J. & Thorne, M. S. A post-perovskite lens and D" heat flux beneath the Central Pacific. Science 314, 1272–1276 (2006).

    Article  Google Scholar 

  19. Li, M., McNamara, A. K. & Garnero, E. J. Chemical complexity of hotspots caused by cycling oceanic crust through mantle reservoirs. Nature Geosci. 7, 336–370 (2014).

    Article  Google Scholar 

  20. Brandenburg, J. P. & van Keken, P. E. Deep storage of oceanic crust in a vigorously convecting mantle. J. Geophys. Res. 112, B06403 (2007).

    Article  Google Scholar 

  21. Nakagawa, T., Tackley, P. J., Deschamps, F. & Connolly, J. A. D. The influence of MORB and harzburgite composition on thermo-chemical mantle convection in a 3-D spherical shell with self-consistently calculated mineral physics. Earth Planet. Sci. Lett. 296, 403–412 (2010).

    Article  Google Scholar 

  22. Grocholski, B., Catalli, K., Shim, S.-H. & Prakapenka, V. B. Mineralogical effects on the detectability of the post-perovskite boundary. Proc. Natl. Acad. Sci. USA 109, 2275–2279 (2012).

    Article  Google Scholar 

  23. Grocholski, B., Shim, S.-H. & Prakapenka, V. B. Stability, metastability, and elastic properties of a dense silica polymorph, seifertite. J. Geophys. Res. 118, B50360 (2013).

    Article  Google Scholar 

  24. Wang, Y. & Wen, L. Complex seismic anisotropy at the border of a very low velocity province at the base of the Earth's mantle. J. Geophys. Res. 112, B09305 (2007).

    Article  Google Scholar 

  25. Lynner, C. & Long, M. D. Lowermost mantle anisotropy and deformation along the boundary of the African LLSVP. Geophys. Res. Lett. 41, 3447–3454 (2014).

    Article  Google Scholar 

  26. Trampert, J., Deschamps, F., Resovsky, J. & Yuen, D. A. Probabilistic tomography maps chemical heterogenities throughout the mantle. Science 306, 853–856 (2004).

    Article  Google Scholar 

  27. Kuo, C. & Romanowicz, B. On the resolution of density anomalies in the Earth's mantle using spectral fitting of normal-mode data. Geophys. J. Int. 150, 1620179 (2002).

    Article  Google Scholar 

  28. Masters, G. & Gubbins, D. On the resolution of density within the Earth. Phys. Earth Planet. In. 140, 159–167 (2003).

    Article  Google Scholar 

  29. Romanowicz, B. Can we resolve 3D density heterogeneity in the lower mantle? Geophys. Res. Lett. 28, 1107–1110 (2001).

    Article  Google Scholar 

  30. Masters, G., Laske, G., Bolton, H. & Dziewonski, A. M. in Earth's Deep Interior (eds Karato, S. et al.) 63–87 (Geophysical Monograph Series Vol. 117, American Geophysical Union, 2000).

    Google Scholar 

  31. Koelemeijer, P., Duess, A. F., Ritsema, J. & van Heijst, H. J. Normal mode insights into the long wavelength velocity and density structure of the lowermost mantle. Abstr. DI33B-02 (American Geophysical Union, Fall Meeting, 2014).

  32. Burke, K., Steinberger, B., Torsvik, T. H. & Smethurst, M. A. Plume generation zones at the margins of large low shear velocity provinces on the core–mantle boundary. Earth Planet. Sci. Lett. 265, 49–60 (2008).

    Article  Google Scholar 

  33. Thorne, M., Garnero, E. J. & Grand, S. P. Geographic correlation between hot spots and deep mantle lateral shear-wave velocity gradients. Phys. Earth Planet. In. 146, 47–63 (2004).

    Article  Google Scholar 

  34. Torsvik, T. H., Burke, K., Steinberger, B., Webb, S. J. & Ashwal, L. D. Diamonds sampled by plumes from the core–mantle boundary. Nature 466, 352–355 (2010).

    Article  Google Scholar 

  35. Davies, D. R., Goes, S. & Sambridge, M. On the relationship between volcanic hotspot locations, the reconstructed eruption sites of large igneous provinces and deep mantle seismic structure. Earth Planet. Sci. Lett. 411, 121–130 (2015).

    Article  Google Scholar 

  36. Steinberger, B. & Torsvik, T. H. A geodynamic model of plumes from the margins of large low shear velocity provinces. Geochem. Geophys. Geosyst. 13, Q01W09 (2012).

    Article  Google Scholar 

  37. Weis, D., Garcia, M. O., Rhodes, J. M., Jellinek, M. & Scoates, J. S. Role of the deep mantle in generating the compositional asymmetry of the Hawaiian mantle plume. Nature Geosci. 4, 831–838 (2011).

    Article  Google Scholar 

  38. Payne, J. A., Jackson, M. G. & Hall, P. S. Parallel volcano trends and geochemical asymmetry of the Society Islands hotspot track. Geology 41, 19–22 (2013).

    Article  Google Scholar 

  39. Farnetani, C. G., Hofmann, A. W. & Class, C. How double volcanic chains sample geochemical anomalies from the lowermost mantle. Earth Planet. Sci. Lett. 359, 240–247 (2012).

    Article  Google Scholar 

  40. McNamara, A. K. & Zhong, S. Thermochemical piles under Africa and the Pacific. Nature 437, 1136–1139 (2005).

    Article  Google Scholar 

  41. Bull, A. L., McNamara, A. K. & Ritsema, J. Synthetic tomography of plume clusters and thermochemical piles. Earth Planet. Sci. Lett. 278, 152–162 (2009).

    Article  Google Scholar 

  42. Zhang, N., Zhong, S., Leng, W. & Li, Z. X. A model for the evolution of the Earth's mantle structure since the Early Paleozoic. J. Geophys. Res. 115, B06401 (2010).

    Article  Google Scholar 

  43. Thompson, P. F. & Tackley, P. J. Generation of mega-plumes from the core–mantle boundary in a compressible mantle with temperature-dependent viscosity. Geophys. Res. Lett. 25, 1999–2002 (1998).

    Article  Google Scholar 

  44. Schubert, G., Masters, G., Olson, P. & Tackley, P. J. Superplumes or plume clusters? Phys. Earth Planet. In. 146, 147–162 (2004).

    Article  Google Scholar 

  45. Schuberth, B. S. A., Bunge, H.-P. & Ritsema, J. Tomographic filtering of high-resolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone? Geochem. Geophys. Geosyst. 10, Q05W03 (2009).

    Google Scholar 

  46. Davies, D. R., Goes, S., Schuberth, B. S. A., Bunge, H. P. & Ritsema, J. Reconciling dynamic and seismic models of Earth's lower mantle: the dominant role of thermal heterogeneity. Earth Planet. Sci. Lett. 353, 253–269 (2012).

    Article  Google Scholar 

  47. Tackley, P. J. in The Core–Mantle Boundary Region (eds Gurnis, M. et al.) 231–253 (Geodynamic Series, American Geophysical Union, 1998).

    Book  Google Scholar 

  48. Nakagawa, T., Tackley, P. J., Deschamps, F. & Connolly, J. A. D. Incorporating self-consistently calculated mineral physics into thermochemical mantle convection simulations in a 3-D spherical shell and its influence on seismic anomalies in Earth's mantle. Geochem. Geophys. Geosyst. 10, Q03004 (2009).

    Article  Google Scholar 

  49. Mulyukova, E., Steinberger, B., Dabrowski, M. & Sobolev, S. V. Survival of LLSVPs for billions of years in a vigorously convecting mantle: replenishment and destruction of chemical anomaly. J. Geophys. Res. 120, 3824–3847 (2015).

    Article  Google Scholar 

  50. Tolstikhin, I. N., Kramers, J. D. & Hofmann, A. W. A chemical Earth model with whole mantle convection: the importance of a core–mantle boundary layer (D") and its early formation. Chem. Geol. 226, 79–99 (2006).

    Article  Google Scholar 

  51. Labrosse, S., Hernlund, J. W. & Coltice, N. A crystallizing dense magma ocean at the base of the Earth's mantle. Nature 450, 866–869 (2007).

    Article  Google Scholar 

  52. Lee, C. T. A. et al. Upside-down differentiation and generation of a 'primordial' lower mantle. Nature 463, 930–933 (2010).

    Article  Google Scholar 

  53. Carlson, R. W. et al. How did early Earth become our modern world? Ann. Rev. Earth Planet. Sci. 42, 151–178 (2014).

    Article  Google Scholar 

  54. Hirose, K., Fei, Y. W., Ma, Y. Z. & Mao, H. K. The fate of subducted basaltic crust in the Earth's lower mantle. Nature 397, 53–56 (1999).

    Article  Google Scholar 

  55. Knittle, E. & Jeanloz, R. Simulating the core–mantle boundary: an experimental study of high-pressure reactions between silicates and liquid iron. Geophys. Res. Lett. 16, 609–612 (1989).

    Article  Google Scholar 

  56. Dubrovinsky, L. et al. Iron-silica interaction at extreme conditions and the electrically conducting layer at the base of Earth's mantle. Nature 422, 58–61 (2003).

    Article  Google Scholar 

  57. Li, M. & McNamara, A. K. The difficulty for subducted oceanic crust to accumulate in upwelling mantle plume regions. J. Geophys. Res. 118, 1–10 (2013).

    Google Scholar 

  58. Davaille, A., Girard, F. & Le Bars, M. How to anchor hotspots in a convecting mantle? Earth Planet. Sci. Lett. 203, 621–634 (2002).

    Article  Google Scholar 

  59. Tan, E. & Gurnis, M. Compressible thermochemical convection and application to lower mantle structures. J. Geophys. Res. 112, B06304 (2007).

    Google Scholar 

  60. Lassak, T. M., McNamara, A. K., Garnero, E. J. & Zhong, S. Core–mantle boundary topography and mantle dynamics. Earth Planet. Sci. Lett. 289, 232–241 (2010).

    Article  Google Scholar 

  61. Soldati, G., Koelemeijer, P., Boschi, L. & Deuss, A. Constraints on core–mantle boundary topography from normal mode splitting. Geochem. Geophys. Geosyst. 14, 1333–1342 (2013).

    Article  Google Scholar 

  62. Lundin, S. et al. Effect of Fe on the equation of state of mantle silicate perovskite over 1 Mbar. Phys. Earth Planet. In. 168, 97–102 (2008).

    Article  Google Scholar 

  63. Fei, Y. et al. Spin transition and equation of state of (Mg, Fe)O solid solution. Geophys. Res. Lett. 34, L17307 (2007).

    Article  Google Scholar 

  64. Irifune, T. et al. Iron partitioning and density changes of pyrolite in Earth's lower mantle. Science 327, 193–195 (2010).

    Article  Google Scholar 

  65. Nakajima, Y., Frost, D. J. & Rubie, D. C. Ferrous iron partitioning between magnesium silicate perovskite and ferropericlase and the composition of perovskite in the Earth's lower mantle. J. Geophys. Res. 117, B08201 (2012).

    Google Scholar 

  66. Jackson, J. M., Zhang, J. Z. & Bass, J. D. Sound velocities and elasticity of aluminous MgSiO3 perovskite: implications for aluminum heterogeneity in Earth's lower mantle. Geophys. Res. Lett. 31, L10614 (2004).

    Article  Google Scholar 

  67. Kawai, K. & Tsuchiya, T. Small shear modulus of cubic CaSiO3 perovskite. Geophys. Res. Lett. 42, 2718–2726 (2015).

    Article  Google Scholar 

  68. Nomura, R. et al. Spin crossover and iron-rich silicate melt in the Earth's deep mantle. Nature 473, 199–202 (2011).

    Article  Google Scholar 

  69. Andrault, D. et al. Solid-liquid iron partitioning in Earth's deep mantle. Nature 487, 354–357 (2012).

    Article  Google Scholar 

  70. Gu, C. et al. Electronic structure of iron in magnesium silicate glasses at high pressure. Geophys. Res. Lett. 39, L24304 (2012).

    Article  Google Scholar 

  71. Kesson, S. E., Fitz Gerald, J. D. & Shelley, J. M. G. Mineral chemistry and density of subducted basaltic crust at lower-mantle pressures. Nature 372, 767–769 (1994).

    Article  Google Scholar 

  72. Deschamps, F., Kaminski, E. & Tackley, P. J. A deep mantle origin for the primitive signature of ocean island basalt. Nature Geosci. 4, 879–882 (2011).

    Article  Google Scholar 

  73. Deschamps, F., Cobden, L. & Tackley, P. J. The primitive nature of large low shear-wave velocity provinces. Earth Planet. Sci. Lett. 349–350, 198–208 (2012).

    Article  Google Scholar 

  74. Holzapfel, C., Rubie, D. C., Frost, D. J. & Langenhorst, F. Fe–Mg interdiffusion in (Mg, Fe)SiO3 perovskite and lower mantle reequilibration. Science 309, 1707–1710 (2005).

    Article  Google Scholar 

  75. Andrault, D. et al. Melting of subducted basalt at the core–mantle boundary. Science 344, 892–895 (2014).

    Article  Google Scholar 

  76. Fiquet, G. et al. Melting of peridotite to 140 gigapascals. Science 329, 1516–1518 (2010).

    Article  Google Scholar 

  77. Nomura, R. et al. Low core–mantle boundary temperature inferred from the solidus of pyrolite. Science 343, 522–525 (2014).

    Article  Google Scholar 

  78. Tsuchiya, J. First principles prediction of a new high-pressure phase of dense hydrous magnesium silicates in the lower mantle. Geophys. Res. Lett. 40, 4570–4573 (2013).

    Article  Google Scholar 

  79. Nishi, M. et al. Stability of hydrous silicate at high pressures and water transport to the deep lower mantle. Nature Geosci. 7, 224–227 (2014).

    Article  Google Scholar 

  80. Ohira, I. et al. Stability of a hydrous δ-phase, AlOOH-MgSiO2(OH)2, and a mechanism for water transport into the base of lower mantle. Earth Planet. Sci. Lett. 401, 21–27 (2014).

    Article  Google Scholar 

  81. Ohtani, E., Amaike, Y., Kamada, S., Sakamaki, T. & Hirao, N. Stability of hydrous phase H MgSiO4H2 under lower mantle conditions. Geophys. Res. Lett. 41, 8283–8287 (2014).

    Article  Google Scholar 

  82. Mosca, I., Cobden, L., Deuss, A., Ritsema, J. & Trampert, J. Seismic and mineralogical structures of the lower mantle from probabilistic tomography. J. Geophys. Res. 117, B06304 (2012).

    Article  Google Scholar 

  83. Seto, Y., Hamane, D., Nagai, T. & Fujino, K. Fate of carbonates within oceanic plates subducted to the lower mantle, and a possible mechanism of diamond formation. Phys. Chem. Miner. 35, 223–229 (2008).

    Article  Google Scholar 

  84. Oganov., A. R., Ono, S., Ma, Y., Glass, C. W. & Garcia, A. Novel high-pressure structures of MgCO3, CaCO3, and CO2 and their role in Earth's lower mantle. Earth Planet. Sci. Lett. 273, 38–47 (2008).

    Article  Google Scholar 

  85. Takafuji, N., Hirose, K., Mitome, M. & Bando, Y. Solubilities of O and Si in liquid iron equilibrium with (Mg, Fe)SiO3 perovskite and the light elements in the core. Geophys. Res. Lett. 32, L06313 (2005).

    Article  Google Scholar 

  86. Ozawa, H. et al. Chemical equilibrium between ferropericlase and molten iron to 134 GPa and implications for iron content at the bottom of the mantle. Geophys. Res. Lett. 35, L05308 (2008).

    Article  Google Scholar 

  87. Frost, D. J. et al. Partitioning of oxygen between the Earth's mantle and core. J. Geophys. Res. 115, B02202 (2010).

    Article  Google Scholar 

  88. Badro, J., Côté, A. S. & Brodholt, J. P. A seismologically consistent compositional model of Earth's core. Proc. Natl. Acad. Sci. USA 111, 7542–7545 (2015).

    Article  Google Scholar 

  89. Manga, M. & Jeanloz, R. Implications of a metal-bearing chemical boundary layer in D" for mantle dynamics. Geophys. Res. Lett. 23, 3091–3094 (1996).

    Article  Google Scholar 

  90. Otsuka, K. & Karato, S.-I. Deep penetration of molten iron into the mantle caused by a morphological instability. Nature 492, 243–246 (2012).

    Article  Google Scholar 

  91. Kanda, R. V. S. & Stevenson, D. J. Suction mechanism for iron entrainment into the lower mantle. Geophys. Res. Lett. 33, L02310 (2006).

    Article  Google Scholar 

  92. Johnson, T. E., Brown, M., Kaus, B. J. P. & VanTongeren, J. A. Delamination and recycling of Archaean crust caused by gravitational instabilities. Nature Geosci. 7, 47–52 (2013).

    Article  Google Scholar 

  93. Hofmann, A. W. & S. R. Hart. Assessment of local and regional isotopic equilibrium in the mantle. Earth Planet. Sci. Lett. 38, 44–62 (1978).

    Article  Google Scholar 

  94. Mukhopadhyay, S. Early differentiation and volatile accretion recorded in deep-mantle neon and xenon. Nature 486, 101–104 (2012).

    Article  Google Scholar 

  95. Ricolleau, A. et al. Phase relations and equation of state of a natural MORB: implications for the density profile of subducted oceanic crust in the Earth's lower mantle. J. Geophys. Res. 115, B08202 (2012).

    Google Scholar 

  96. Williams, C. D., Li, M., McNamara, A. K., Garnero, E. J. & van Soest, M. C. Episodic entrainment of deep primordial mantle material into ocean island basalts. Nature Commun. 6, 8937 (2015).

    Article  Google Scholar 

  97. McDonough, W. F. & Sun, S.-S. The composition of the Earth. Chem. Geol. 120, 223–253 (1995).

    Article  Google Scholar 

  98. Schilling, J.-G. et al. Petrologic and geochemical variations along the mid-Atlantic ridge from 29°N to 73°N. Am. J. Sci. 283, 510–586 (1983).

    Article  Google Scholar 

  99. Kesson, S. E., Fitz Gerald, J. D. & Shelley, J. M. Mineralogy and dynamics of a pyrolite lower mantle. Nature 393, 252–255 (1998).

    Article  Google Scholar 

  100. Hirose, K., Takafuji, N., Sata, N. & Ohishi, Y. Phase transition and density of subducted MORB crust in the lower mantle. Earth Planet. Sci. Lett. 237, 239–251 (2005).

    Article  Google Scholar 

Download references

Acknowledgements

The authors thank T. Torsvik for the LIP and kimberlite data set, seismic tomographers that made their models publically available, D.A. Frost and P. Koelemeijer for fruitful discussions, and J. Ritsema, F. Deschamps and A. Stracke for abundant helpful comments. M. Li provided model results and images from ref. 19 that were the basis of Supplementary Fig. S6. This research was partially supported by National Science Foundation grants EAR1401270, EAR1161038 and EAR1338810.

Author information

Authors and Affiliations

  1. School of Earth and Space Exploration, Arizona State University, Tempe, 85287-6004, Arizona, USA

    Edward J. Garnero, Allen K. McNamara & Sang-Heon Shim

Authors
  1. Edward J. Garnero
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Allen K. McNamara
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Sang-Heon Shim
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

E.J.G., A.K.M., and S.-H.S. equally contributed to the text. E.J.G. constructed the figures with active involvement from A.K.M. and S.-H.S.

Corresponding author

Correspondence to Edward J. Garnero.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 3755 kb)

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Garnero, E., McNamara, A. & Shim, SH. Continent-sized anomalous zones with low seismic velocity at the base of Earth's mantle. Nature Geosci 9, 481–489 (2016). https://doi.org/10.1038/ngeo2733

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/ngeo2733

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing