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Seismological constraints on a possible plume root at the core–mantle boundary

Abstract

Recent seismological discoveries have indicated that the Earth's core–mantle boundary is far more complex than a simple boundary between the molten outer core and the silicate mantle. Instead, its structural complexities probably rival those of the Earth's crust1. Some regions of the lowermost mantle have been observed to have seismic wave speed reductions of at least 10 per cent2,3,4,5,6,7, which appear not to be global in extent7,8,9. Here we present robust evidence for an 8.5-km-thick and 50-km-wide pocket of dense, partially molten material at the core–mantle boundary east of Australia. Array analyses of an anomalous precursor to the reflected seismic wave ScP reveal compressional and shear-wave velocity reductions of 8 and 25 per cent, respectively, and a 10 per cent increase in density of the partially molten aggregate. Seismological data are incompatible with a basal layer composed of pure melt, and thus require a mechanism to prevent downward percolation of dense melt within the layer. This may be possible by trapping of melt by cumulus crystal growth following melt drainage from an anomalously hot overlying region of the lowermost mantle. This magmatic evolution and the resulting cumulate structure seem to be associated with overlying thermal instabilities, and thus may mark a root zone of an upwelling plume.

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Figure 1: Array beams of ScP and precursors.
Figure 2: ULVZ detections at ScP core-reflection locations.
Figure 3: Synthetic waveform modelling of ScP precursors.
Figure 4: Preferred model of dense partially molten ULVZ.

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References

  1. Garnero, E. J. Heterogeneity of the lowermost mantle. Annu. Rev. Earth Planet. Sci. 28, 509–537 (2000)

    Article  ADS  Google Scholar 

  2. Mori, J. & Helmberger, D. V. Localized boundary layer below the mid-Pacific velocity anomaly from a PcP precursor. J. Geophys. Res. 100, 20359–20365 (1995)

    Article  ADS  Google Scholar 

  3. Garnero, E. J. & Helmberger, D. V. Further structural constraints and uncertainties of a thin laterally varying ultralow-velocity layer at the base of the mantle. J. Geophys. Res. 103, 12495–12509 (1998)

    Article  ADS  Google Scholar 

  4. Reasoner, C. & Revenaugh, J. ScP constraints on ultralow-velocity zone density and gradient thickness beneath the Pacific. J. Geophys. Res. 105, 28173–28182 (2000)

    Article  ADS  Google Scholar 

  5. Rost, S. & Revenaugh, J. Small-scale ultralow-velocity zone structure imaged by ScP. J. Geophys. Res. 108(B1), 2056, doi:10.1029/2001JB001627 (2003)

    Article  ADS  Google Scholar 

  6. Rondenay, S. & Fischer, K. M. Constraints on localized core-mantle boundary structure from multichannel, broadband SKS coda analysis. J. Geophys. Res. 108(B11), 2537, doi:10.1029/2003JB002518 (2003)

    Article  ADS  Google Scholar 

  7. Thorne, M. & Garnero, E. J. Inferences on ultralow-velocity zone structure from a global analysis of SPdKS waves. J. Geophys. Res. 109, B08301, doi:10.1029/2004JB003010 (2004)

    Article  ADS  Google Scholar 

  8. Castle, J. C. & Van der Hilst, R. D. The core-mantle boundary under the Gulf of Alaska: No ULVZ for shear waves. Earth Planet. Sci. Lett. 176, 311–321 (2000)

    Article  ADS  CAS  Google Scholar 

  9. Persh, S. E. & Vidale, J. E. Reflection properties of the core-mantle boundary from global stacks of PcP and ScP. J. Geophys. Res. 109, B04309, doi:10.1029/2003JB002768 (2004)

    ADS  Google Scholar 

  10. Williams, Q. & Garnero, E. J. Seismic evidence for partial melt at the base of Earth's mantle. Science 273, 1528–1530 (1996)

    Article  ADS  CAS  Google Scholar 

  11. Vidale, J. E. & Hedlin, M. A. H. Evidence for partial melt at the core-mantle boundary north of Tonga from the strong scattering of seismic waves. Nature 391, 682–685 (1998)

    Article  ADS  CAS  Google Scholar 

  12. Knittle, E. & Jeanloz, R. Earth's core-mantle boundary; results of experiments at high pressures and temperatures. Science 251, 1438–1443 (1991)

    Article  ADS  CAS  Google Scholar 

  13. Song, X. & Ahrens, T. J. Pressure-temperature range of reactions between liquid iron in the outer core and mantle silicates. Geophys. Res. Lett. 21, 153–156 (1994)

    Article  ADS  CAS  Google Scholar 

  14. Berryman, J. G. Seismic velocity decrement ratios for regions of partial melt in the lower mantle. Geophys. Res. Lett. 27, 421–424 (2000)

    Article  ADS  Google Scholar 

  15. Murakami, M., Hirose, K., Kawamura, K., Sata, N. & Ohishi, Y. Post-perovskite phase transition in MgSiO3 . Science 304, 855–858 (2004)

    Article  ADS  CAS  Google Scholar 

  16. Karason, H. & van der Hilst, R. D. Tomographic imaging of the lowermost mantle with differential times of refracted and diffracted core phases (PKP, Pdiff). J. Geophys. Res. 106, 6569–6587 (2001)

    Article  ADS  Google Scholar 

  17. Grand, S. P. Mantle shear-wave tomography and the fate of subducted slabs. Phil. Trans. R. Soc. Lond. A 360, 2475–2491 (2002)

    Article  ADS  Google Scholar 

  18. Rost, S. & Revenaugh, J. Seismic detection of rigid zones at the top of the core. Science 294, 1911–1914 (2001)

    Article  ADS  CAS  Google Scholar 

  19. Garnero, E. J. & Vidale, J. E. ScP; a probe of ultralow velocity zones at the base of the mantle. Geophys. Res. Lett. 26, 377–380 (1999)

    Article  ADS  Google Scholar 

  20. Cerveny, V. & Psencik, I. Gaussian beams in elastic 2-D laterally varying layered structures. Geophys. J. Int. 78, 65–91 (1984)

    Article  ADS  Google Scholar 

  21. Garnero, E. J., Revenaugh, J., Williams, Q., Lay, T. & Kellogg, L. H. in The Core-Mantle Boundary Region (eds Gurnis, M., Wysession, M., Knittle, E. & Buffett, B.) 319–334 (Geodynamics series, Vol. 28, American Geophysical Union, Washington DC, 1998)

    Book  Google Scholar 

  22. Dobson, D. P. & Brodholt, J. P. Subducted iron formations as a source of ultra-low-velocity zones at the core-mantle boundary. Nature 434, 371–374 (2005)

    Article  ADS  CAS  Google Scholar 

  23. McKenzie, D. P. The extraction of magma from the crust and mantle. Earth Planet. Sci. Lett. 74, 81–91 (1985)

    Article  ADS  CAS  Google Scholar 

  24. Roscoe, R. The viscosity of suspensions of rigid spheres. J. Appl. Phys. 3, 267–269 (1952)

    Google Scholar 

  25. Akins, J. A., Luo, S.-N., Asimow, P. D. & Ahrens, T. J. Shock-induced melting of MgSiO3 perovskite and implications for melts in Earth's lowermost mantle. Geophys. Res. Lett. 31(14), doi:10.1029/2004GL020237 (2004)

  26. Knittle, E. in The Core-Mantle Boundary Region (eds Gurnis, M., Wysession, M., Knittle, E. & Buffett, B.) 119–130 (Geodynamics Series, Vol. 28, American Geophysical Union, Washington DC, 1998)

    Book  Google Scholar 

  27. Williams, Q., Revenaugh, J. & Garnero, E. J. A correlation between ultra-low basal velocities in the mantle and hot spots. Science 281, 546–549 (1998)

    Article  ADS  CAS  Google Scholar 

  28. Walker, D., Agee, C. & Zhang, Y. Fusion curve slope and crystal/liquid buoyancy. J. Geophys. Res. 93, 313–323 (1988)

    Article  ADS  Google Scholar 

  29. Montelli, R. et al. Finite-frequency tomography reveals a variety of plumes in the mantle. Science 303, 338–343 (2004)

    Article  ADS  CAS  PubMed Central  Google Scholar 

  30. Steinberger, B. Plumes in a convecting mantle: Models and observations for individual hotspots. J. Geophys. Res. 105, 11127–11152 (2000)

    Article  ADS  Google Scholar 

  31. Jellinek, A. M. & Manga, M. The influence of a chemical boundary layer on the fixity, spacing and lifetime of mantle plumes. Nature 418, 760–763 (2002)

    Article  ADS  CAS  Google Scholar 

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Acknowledgements

We thank R. van der Hilst and S. Grand for supplying tomographic models, S. Grand for a Futterman t* code, and the Seismological group of MoD at Blacknest for the WRA data set. This research was supported by NSF.

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Correspondence to Sebastian Rost.

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Supplementary information

Supplementary Materials

Additional tests and methods, and legends for the two Supplementary Figures. This file also contains Supplementary Table S1, which details earthquake location and origin time information for events showing ScP precursory energy (DOC 54 kb)

Supplementary Figure S1

Map view of the best fit t* values. The best-fit t* operators where found by convolving The P-wavelet with the t* operator in the frequency domain and comparing the resultant waveform to the ScP wavelet. (PDF 210 kb)

Supplementary Figure S2a and b.

Subfigures a and b of Supplementary Figure S2 a) Synthetic waveforms for varying density change (p) and fixed P-wave velocity change: α(-10%), S-wave velocity change: β(-10%) and ULVZ thickness: D (8.5km). b) Synthetic waveforms for varying density and fixed α(-10%), β(-25%) and D (8.5km). (PDF 300 kb)

Supplementary Figure S2c

Part c of Supplementary Figure S2 c) Synthetic waveforms for varying βand fixed α(-10%), p(+10%) and D (8.5km). (PDF 242 kb)

Supplementary Figure S2d and e

Contains: Parts d and e of Supplementary Figure S2 c) Synthetic waveforms for varying α and fixed p(0%), β(-25%) and D (8.5km). d) Synthetic waveforms for varying α and fixed p(+10%), β(-25%) and D (8.5km). (PDF 254 kb)

Supplementary Figure S2f and g.

Parts f and g of Supplementary Figure S2 f) Synthetic waveforms for fixed α:β= 1:1 (absolute values vary) and fixed p(+10%), and D (8.5km). g) Synthetic waveforms for fixed α:β= 1:3 (absolute values vary) and fixed p(+10%), and D (8.5km). (PDF 221 kb)

Supplementary Figure S2h and i

Parts h and i of Supplemental Figure 2 h) Synthetic waveforms for varying thickness and fixed α(-10%), β(-25%) and p(0%) i) Synthetic waveforms for varying thickness and fixed α(-10%), β(-25%) and p(+10%). (PDF 257 kb)

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Rost, S., Garnero, E., Williams, Q. et al. Seismological constraints on a possible plume root at the core–mantle boundary. Nature 435, 666–669 (2005). https://doi.org/10.1038/nature03620

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