Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle

Article metrics

Abstract

Mounting evidence indicates that the Earth's mantle is chemically heterogeneous. To understand the forms that convection might take in such a mantle, I have conducted laboratory experiments on thermochemical convection in a fluid with stratified density and viscosity. For intermediate density contrasts, a ‘doming’ regime of convection is observed, in which hot domes oscillate vertically through the whole layer while thin tubular plumes rise from their upper surfaces. These plumes could be responsible for the ‘hot spots’ and the domes themselves for the ‘superwells’ observed at the Earth's surface. In the Earth's mantle, the doming regime should occur for density contrasts less than about 1%. Moreover, quantitative scaling laws derived from the experiments show that the mantle might have evolved from strictly stratified convection 4 Gyr ago to doming today. Thermochemical convection can thus reconcile the survival of geochemically distinct reservoirs with the small amplitude of present-day density heterogeneities inferred from seismology and mineral physics.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Snapshots and vertical temperature structure for the different regimes of convection.
Figure 2: Different convective regimes as a function of the buoyancy ratio Rρ and the viscosity ratio γ.
Figure 3: Doming regime.
Figure 4: Critical density contrast Δρ/ρ calculated from equation (2) as a function of the temperature difference ΔT driving convection.
Figure 5: Volumetric entrainment rate of a cylindrical plume as a function of (γRρ)-1.

References

  1. 1

    Olson,P., Silver,P. G. & Carlson,R. W. The large scale structure of convection in the Earth's mantle. Nature 344, 209–215 (1990).

  2. 2

    Dziewonski,A. M. & Anderson,D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981).

  3. 3

    Jackson,I. Elasticity, composition and temperature of the Earth's lower mantle: a reappraisal. Geophys. J. Int. 134, 291–311 (1998).

  4. 4

    Bina,C. R. in Ultra-high Pressure Mineralogy (ed. Hemley, R. J.) 205–239 (Reviews in Mineralogy Vol. 37, Mineralogical Society of America, Washington, DC, 1998).

  5. 5

    Zindler,A. & Hart,S. Chemical geodynamics. Annu. Rev. Earth Planet. Sci. 14, 493–571 (1986).

  6. 6

    Lay,T., Williams,Q. & Garnero,E. J. The core–mantle boundary layer and deep Earth dynamics. Nature 392, 461–467 (1998).

  7. 7

    Van der Hilst,R. D., Widiyantoro,S. & Engdahl,E. R. Evidence for deep mantle circulation from global tomography. Nature 386, 578–584 (1997).

  8. 8

    Forte,A. M. & Woodward,R. L. Seismic-geodynamics constraints on three-dimensional structure, vertical flow, and heat transfer in the mantle. J. Geophys. Res. 102, 17981–17994 (1997).

  9. 9

    Wilson,J. T. Evidence from islands on the spreading of the ocean floor. Can. J. Phys. 41, 863–868 (1963).

  10. 10

    Morgan,W. J. Plate motions and deep mantle convection. Nature 230, 42–43 (1971).

  11. 11

    Richards,M. A., Duncan,R. A. & Courtillot,V. E. Flood basalts and hot-spot tracks: Plume heads and tails. Science 246, 103–107 (1989).

  12. 12

    Sleep,N. H. Hotspots and mantle plumes: some phenomenology. J. Geophys. Res. 95, 6715–6736 (1990).

  13. 13

    Loper,D. E. & Stacey,F. D. Mantle plumes and the periodicity of magnetic field reversals. Geophys. Res. Lett. 13, 1525–1528 (1986).

  14. 14

    Larson,R. L. & Olson,P. Mantle plumes control magnetic reversal frequency. Earth Planet. Sci. Lett. 107, 437–447 (1991).

  15. 15

    McNutt,M. K. Superswells. Rev. Geophys. 36, 211–244 (1998).

  16. 16

    Nyblade,A. A. & Robinson,S. W. The African superswell. Geophys. Res. Lett. 21, 765–768 (1994).

  17. 17

    McNutt,M. K. & Fisher,K. M. in Seamounts, Islands and Atolls (eds Keating, B. H. et al.) 25–34 (Geophys. Monogr. Ser. 43, American Geophysical Union, Washington DC, 1987).

  18. 18

    Masters,G., Johnson,S., Laske,G. & Bolton,H. A shear-velocity model of the mantle. Phil. Trans. R. Soc. Lond. A 354, 1385–1410 (1996).

  19. 19

    Hart,S. R. A large-scale isotope anomaly in the Southern Hemisphere mantle. Nature 309, 753–757 (1984).

  20. 20

    Cazenave,A. & Thoraval,C. Mantle dynamics constrained by degree 6 surface topography, seismic tomography and geoid: Inference on the origin of the South Pacific Superswell. Earth Planet. Sci. Lett. 122, 207–219 (1994).

  21. 21

    Vinnik,L., Chevrot,S. & Montagner,J.-P. Evidence for a stagnant plume in the transition zone. Geophys. Res. Lett. 24, 1007–1010 (1997).

  22. 22

    Larson,R. L. Geological consequences of superplumes. Geology 19, 547–550 (1991).

  23. 23

    Bercovici,D., Schubert,G. & Glatzmaier,G. A. Three-dimensional spherical models of convection in the Earth's mantle. Science 244, 950–955 (1989).

  24. 24

    Albers,M. & Christensen,U. R. The excess temperature of plumes rising from the core-mantle boundary. Geophys. Res. Lett. 23, 3567–3570 (1996).

  25. 25

    Farnetani,C. G. Excess temperature of mantle plumes: the role of chemical stratification across D″. Geophys. Res. Lett. 24, 1583–1586 (1997).

  26. 26

    Hoffman,N. R. A. & McKenzie,D. P. The destruction of geochemical heterogeneities by differential motions during mantle convection. Geophys. J. R. Astron. Soc. 82, 163–206 (1985).

  27. 27

    Christensen,U. Mixing by time-dependent convection. Earth Planet. Sci. Lett. 95, 382–394 (1989).

  28. 28

    Kellogg,L. H. Chaotic mixing in the Earth's mantle. Adv. Geophys. 34, 1–33 (1993).

  29. 29

    Gurnis,M. & Davies,G. F. The effect of depth-dependent viscosity on convective mixing in the mantle and the possible survival of primitive mantle. Geophys. Res. Lett. 13, 541–544 (1986).

  30. 30

    Spence,D. A., Ockendon,J. R., Wilmott,P., Turcotte,D. L. & Kellogg,L. H. Convective mixing in the mantle: the role of viscosity differences. Geophys. J. 95, 79–86 (1988).

  31. 31

    Manga,M. Mixing of heterogeneities in the mantle—Effects of viscosity differences. Geophys. Res. Lett. 23, 403–406 (1996).

  32. 32

    Olson,P. An experimental approach to thermal convection in a two-layered mantle. J. Geophys. Res. 89, 11293–11301 (1984).

  33. 33

    van Keken,P. E. & Ballentine,C. J. Whole-mantle versus layered mantle convection and the role of a high-viscosity lower mantle in terrestrial volatile evolution. Earth Planet. Sci. Lett. 156, 19–32 (1998).

  34. 34

    Davaille,A. Two-layer thermal convection in miscible viscous fluids. J. Fluid Mech. 379, 223–253 (1999).

  35. 35

    Richter,F. M. & Johnson,C. E. Stability of a chemically layered mantle. J. Geophys. Res. 79, 1635–1639 (1974).

  36. 36

    Richter,F. M. & McKenzie,D. P. On some consequences and possible causes of layered convection. J. Geophys. Res. 86, 6133–6124 (1981).

  37. 37

    Christensen,U. Instability in a hot boundary layer and initiation of thermochemical plumes. Ann. Geophys. 2, 311–320 (1984).

  38. 38

    Tackley,P. J. in The Core-Mantle Boundary Region (eds Gwinis, M. et al.) 231–255 (AGU Monogr, American Geophysical Union, Washington DC, 1998).

  39. 39

    Olson,P. & Kincaid,C. Experiments on the interaction of thermal convection and compositional layering at the base of the mantle. J. Geophys. Res. 96, 4347–4354 (1991).

  40. 40

    Karato,S. & Wu,P. Rheology of the upper mantle: a synthesis. Science 260, 771–778 (1993).

  41. 41

    Chopelas,A. & Boehler,R. Thermal expansivity in the lower mantle. Geophys. Res. Lett. 19, 1983–1986 (1992).

  42. 42

    Kellogg,L. H., Hager,B. H. & van der Hilst,R. D. Compositional stratification in the deep mantle. Science 283, 1881–1884 (1999).

  43. 43

    Boelher,R. Temperatures in the Earth's core from melting point measurements of iron at high static pressures. Nature 363, 534–536 (1993).

  44. 44

    Allègre,C. J. & Lewin,E. Isotopic systems and stirring times of the earth's mantle. Earth Planet. Sci. Lett. 136, 629–646 (1995).

  45. 45

    Sleep,N. H. Gradual entrainment of a chemical layer at the base of the mantle by overlying convection. Geophys. J. 95, 437–447 (1988).

  46. 46

    Montague,N. L., Kellogg,L. H. & Manga,M. High-Rayleigh number thermochemical models of a dense boundary layer in D″. Geophys. Res. Lett. 25, 2345–2348 (1998).

  47. 47

    Girard,F. & Davaille,A. Dynamics of an heterogeneous layer at the base of the mantle: an experimental approach. Eos 79, 617 (1998).

Download references

Acknowledgements

I thank C. Allègre, C. Jaupart, K. Turekian, P. Molnar, N. Ribe and G. Veronis for discussions; G. Bienfait, F. Girard, A. Lee, W. Phelps and W. Sacco for help in the laboratory; and M. McNutt, M. Manga and P. Tackley for comments on the manuscript. Part of this work was done at the Department of Geology and Geophysics at Yale University, USA.

Author information

Correspondence to Anne Davaille.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Davaille, A. Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle. Nature 402, 756–760 (1999) doi:10.1038/45461

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.