Advertisement

Hotspots and the Case for a High Viscosity Lower Mantle

  • Mark A. Richards
Chapter
Part of the NATO ASI Series book series (ASIC, volume 334)

Abstract

There are two obvious forms of convection in the Earth’s mantle: Plate-scale flow with upwellings at mid-ocean ridges and downwellings at subduction zones, and narrow upwelling plumes from the deep mantle which give rise to volcanic hotspots. Hotspots have relative motions which are at least an order of magnitude less than relative plate motions, and these two styles of convection appear to be decoupled on timescales of ~100–200 m.y. Also, hotspot basalts have trace element and isotopic signatures of mantle source regions which have been isolated from the upper mantle mid-ocean ridge source for a significant fraction of Earth history. These observations are compatible with whole mantle convection models which include a viscosity increase with depth. Lower mantle strain (mixing) rates and horizontal motions at, e.g., the core-mantle boundary are sufficiently reduced if lower mantle viscosity is about 1–2 orders of magnitude greater than that of the upper mantle. Such models also explain the depth distribution and focal mechanisms of deep earthquakes in subducted slabs as well as the long-wavelength geoid highs over subduction zones. Relatively isoviscous, chemically stratified convection models can probably satisfy the constraints from hotspot fixity and geochemistry. However, none of these observations has been shown to be compatible with models of whole-mantle convection which do not include a substantial increase in viscosity with depth.

Keywords

Subduction Zone Mantle Plume Plate Motion Lower Mantle Mantle Convection 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Allegre, C.J., T. Staudacher, and P. Sarda, 1987. Rare gas systematics: formation of the atmosphere, evolution and structure of the Earth’s mantle, Earth Planet. Sci. Lett., 81, 127–150.CrossRefGoogle Scholar
  2. Betz, F. and H.H. Hess, 1942. The floor of the north Pacific ocean, Geogr. Rev., 32, 99–116.CrossRefGoogle Scholar
  3. Burke, K., W.S.F. Kidd, and J.T. Wilson, 1973. Relative and latitudinal motion of Atlantic hot spots, Nature, 245, 133–137.CrossRefGoogle Scholar
  4. Chase, 1981. Oceanic island Pb: Two-stage histories and mantle evolution, Earth Planet. Sci. Lett., 52, 277–284.CrossRefGoogle Scholar
  5. Davies, G.F., 1984. Geophysical and isotopic constraints on mantle convection: an interim synthesis, J. Geophys. Res., 89, 6017–6040.CrossRefGoogle Scholar
  6. Davies, G.F., 1988. Ocean bathymetry and mantle convection 1. Large-scale flow and hotspots, J. Geophys. Res., 93, 10467–10480.CrossRefGoogle Scholar
  7. Davies, G.F., 1990. Mantle plumes, mantle stirring, and hotspot chemistry, Earth Planet. Sci. Lett., in press.Google Scholar
  8. DePaolo, D.J., 1981. Nd isotopic studies: Some new perspectives on Earth structure and evolution, EOS, 62, 137–140.CrossRefGoogle Scholar
  9. DePaolo, D.J. and G.J. Wasserburg, 1976. Nd isotopic variations and petrogenetic models, Geophys. Res. Lett., 3, 249–252.CrossRefGoogle Scholar
  10. Duncan, 1981. Hotspots in the southern oceans - an absolute frame of reference for motion of the Gondwana continents, Tectonophysics, 74, 29–42.CrossRefGoogle Scholar
  11. Duncan, R.A. and D.A. Clague, 1985. Pacific plate motion recorded by linear volcanic chains, in The Ocean Basins and Margins, 7A, A.E.M. Nairn, F.G. Stehli and S. Uyeda (eds.), Plenum (New York), 89–121.CrossRefGoogle Scholar
  12. Duncan, R.A. and M.A. Richards, 1990. Hotspots, flood basalts, and true polar wander, Rev. Geophys., in press.Google Scholar
  13. Engebretson, D.C., A. Cox, and R.G. Gordon, 1985. Relative motions between oceanic and continental plates in the Pacific basin, Geol. Soc. Am. Special Paper 206, GSA Publ., Boulder, CO.Google Scholar
  14. Forte, A.M. and W.R. Peltier, 1987. Plate tectonics and aspherical Earth structure: The importance of poloidal-toroidal coupling, J. Geophys. Res., 92, 3645–3679.CrossRefGoogle Scholar
  15. Galer, S.J.G., S.L. Goldstein, and R.K. O’Nions, 1989. Limits on chemical and convective isolation in the Earth’s interior, Chem. Geol., 75, 257–290.CrossRefGoogle Scholar
  16. Griffiths, R.W. and M.A. Richards, 1989. The adjustment of mantle plumes to changes in plate motion, Geophys. Res. Lett., 16, 437–440.CrossRefGoogle Scholar
  17. Gurnis, M. and G.F. Davies, 1986a. Numerical study of high Rayleigh number convection in a medium with depth-dependent viscosity, Geophys. J. Roy. Astron. Soc., 85, 523–541.CrossRefGoogle Scholar
  18. Gurnis, M. and G.F. Davies, 1986b. The effect of depth-dependent viscosity on convective mixing in the mantle and the possible survival of primitive lower mantle, Geophys. Res. Lett., 13, 541–544.CrossRefGoogle Scholar
  19. Gurnis, M. and B.H. Hager, 1988. Controls on the structure of subducted slabs, Nature, 335, 317–321.CrossRefGoogle Scholar
  20. Hager, B.H. and R.J. O’Connell, 1981. A simple global model of plate dynamics and mantle convection, J. Geophys. Res., 86, 4843–4867.CrossRefGoogle Scholar
  21. Hager, B.H., R.W. Clayton, M.A. Richards, A.M. Dziewonski, and R.P. Comer, 1985. Lower mantle heterogeneity, dynamic topography, and the geoid, Nature, 313, 541–545.CrossRefGoogle Scholar
  22. Hager, B.H. and M.A. Richards, 1989. Long-wavelength variations in Earth’s geoid: physical models and dynamical implications, Phil. Trans. R. Soc. Lond., A328, 309–327.CrossRefGoogle Scholar
  23. Hart, S.R., 1971. K, Rb, Cs, Sr, and Ba contents and Sr isotope rations of ocean floor basalts, Phil Trans. Roy. Soc. Lond., A268, 573–587.Google Scholar
  24. Hart, S.R., J.G. Schilling, and J.L. Powell, 1973. Basalts from Iceland and along the Reykjanes Ridge: Sr isotope geochemistry, Nature Physical Science, 246, 104–107.Google Scholar
  25. Hoffman, A.W., 1984. Geochemical mantle models, Terra Cognita, 4, 157–165.Google Scholar
  26. Hoffman, N.R.A. and D.P. McKenzie, 1985. The destruction of geochemical heterogeneities by differential fluid motions during mantle convection, Geophys. J. Roy. Astron. Soc., 82, 163–206.CrossRefGoogle Scholar
  27. Hong, H.J., and D.A. Yuen, 1985. Dynamical consequences on surface deformations and geoids from equation of state (abstract), EOS Trans. AGU, 66, 1075.Google Scholar
  28. Hong, H.J. and D.A. Yuen, 1990. Dynamical effects from equation of state on topographies and geoid anomalies due to internal loading, J. Geophys. Res., in press.Google Scholar
  29. Hughes, T.J.R., W.K. Liu, and A. Brooks, 1979. Finite element analysis of incompressible viscous flows by the penalty function formulation, J. Comput. Phys., 30, 1–60.CrossRefGoogle Scholar
  30. Isaacks, B. and P. Molnar, 1971. Distribution of stresses in the descending lithosphere from a global survey of focal mechanism solutions of mantle earthquakes, Rev. Geophys. Space Phys., 9, 103–174.CrossRefGoogle Scholar
  31. Ito, E. and E. Takahashi, 1989. Postspinel transformations in the system Mg2SiO4-Fe2SiO4 and some geophysical implications, J. Geophys. Res., 94, 10637–10646.CrossRefGoogle Scholar
  32. Jackson, E.D., E.A. Silver, and G.B. Dalrymple, 1972. Hawaiian-Emperor Chain and its relation to Cenozoic circumpacific tectonics, Geol. Soc. Am Bull., 83, 601–618.CrossRefGoogle Scholar
  33. Mahoney, J.J., 1988. The Deccan Traps, in Continental Flood Basalts J.D. MacDougall (ed.), Kluwer Academic Publ. ((Dordrecht), pp. 151–104.CrossRefGoogle Scholar
  34. McKenzie, D.P. and M.J. Bickle, 1988. The volume and composition of melt generated by extension of the lithosphere, J. Petrol., 29, 625–679.CrossRefGoogle Scholar
  35. Minster, J.B., T.H. Jordan, P. Molnar, and E. Haines, 1974. Numerical modelling of instantaneous plate motions, Geophys. J. Roy. Astr. Soc., 36, 541–576.CrossRefGoogle Scholar
  36. Minster, J.B. and T.H. Jordan, 1978. Present-day plate motions, J. Geophys. Res., 83, 5331–5354.CrossRefGoogle Scholar
  37. Molnar, P. and T. Atwater, 1973. Relative motions of hotspots in the mantle, Nature, 246, 288–291.CrossRefGoogle Scholar
  38. Molnar, P. and J. Francheteau, 1975. The relative motion of hotspots in the Atlantic and Indian Oceans during the Cenozoic, Geophys. J. R. Astr. Soc., 43, 763–774.CrossRefGoogle Scholar
  39. Molnar, P. and J. Stock, 1987. Relative motions of hotspots in the Pacific, Atlantic, and Indian Oceans since late Cretaceous time, Nature, 327, 587–591.CrossRefGoogle Scholar
  40. Morgan, W.J., 1972. Plate motions and deep mantle convection, Mem. Geol. Soc Am., 132, 7–22.Google Scholar
  41. Morgan, W.J., 1981. Hotspot tracks and the opening of the Atlantic and Indian Oceans, in The Sea, vol. 10, C. Emiliani, ed., Wiley, New York.Google Scholar
  42. Morgan, W.J., 1983. Hotspot tracks and the early rifting of the Atlantic, Tectonophysics, 94, 123–139.CrossRefGoogle Scholar
  43. O’Connell, R.J. and B.H. Hager, 1980. On the thermal state of the Earth, in Physics of the Earth’s Interior, edited by A. Dziewonski and E. Boschi, pp. 270–317, North-Holland, Amsterdam.Google Scholar
  44. O’Nions, R.K., P.J. Hamilton, and N.M. Evensen, 1977. Variations in 143Nd/144Nd and 87Sr/86Sr ratios in oceanic basalts, Earth Planet. Sci. Lett., 34, 13–22.CrossRefGoogle Scholar
  45. Ricard, J., L. Fleitout, and C. Froidevaux, 1984. Geoid heights and lithospheric stresses for a dynamical Earth, Ann. Geophys., 2, 267–286.Google Scholar
  46. Ricard, J., C. Vigny, and C. Froidevaux, 1989. Mantle heterogeneities, geoid, and plate motion: a Monte Carlo inversion, J. Geophys. Res., 94, 13739–13754.CrossRefGoogle Scholar
  47. Richards, M.A. and G.F. Davies, 1989. On the separation of relatively buoyant components from subducted lithosphere, Geophys. Res. Lett., 16, 831–834.CrossRefGoogle Scholar
  48. Richards, M.A. and D.C. Engebretson, 1990. The history of subduction, the distribution of hotspots, seismic heterogeneity, and the large-scale structure of mantle convection (abstract), EOS Trans. AGU Fall Meeting, in press.Google Scholar
  49. Richards, M.A. and R.W. Griffiths, 1988. Deflection of plumes by mantle shear flow. Experimental results and a simple theory, Geophys. J. Roy. Astron. Soc., 94, 367–376.CrossRefGoogle Scholar
  50. Richards, M.A. and B.H. Hager, 1984. Geoid anomalies in a dynamic Earth, J. Geophys. Res., 89, 5487–6002.Google Scholar
  51. Richards, M.A. and B.H. Hager, 1988. The Earth’s geoid and the large-scale structure of mantle convection, in The Physics of Planets, edited by S.K. Runcorn, pp. 247–272, John Wiley, New York.Google Scholar
  52. Richards, M.A., B.H. Hager, and N.H. Sleep, 1988, Dynamically supported geoid highs over hotspots: Observation and theory, J. Geophys. Res., 93, 7690–7708.CrossRefGoogle Scholar
  53. Richards, M.A. and C.W. Wicks, 1990. S-P conversion from the transition zone beneath Tonga and the nature of the 670 km discontinuity, Geophys. J. Int., 101, 1–35.CrossRefGoogle Scholar
  54. Schilling, J.G., 1971. Sea-floor evolution: Rare earth evidence, Phil. Trans. Roy. Soc. Long., A268, 663–706.CrossRefGoogle Scholar
  55. Schilling, J.G., 1973. Iceland mantle plume: geochemical evidence along Reykjanes Ridge, Nature, 242, 565–571.CrossRefGoogle Scholar
  56. Sleep, N.H., 1974. Segregation of magma from a mostly crystalline mush, Geol. Soc. Am. Bull., 85, 1225–1232, 1974.CrossRefGoogle Scholar
  57. Sleep, N.H., 1984. Tapping of magmas from ubiquitous mantle heterogeneities: An alternative to mantle plumes?, J. Geophys. Res., 89, 10029–10041.CrossRefGoogle Scholar
  58. Sleep, N.H., 1990. Hotspots and mantle plumes: Some phenomenology, in press, J. Geophys. Res..Google Scholar
  59. Stock, J. and P. Molnar, 1987. Revised history of early Tertiary plate motion in the southwest Pacific, Nature, 325, 495–499.CrossRefGoogle Scholar
  60. Tatsumoto, M. 1978. Composition of lead in oceanic basalt and its implication to mantle evolution, Earth Planet. Sci. Lett., 38, 63–87.CrossRefGoogle Scholar
  61. Turcotte, D.L. and E.R. Oxburgh, 1976. Stress accumulation in the lithosphere, Tectonophysics, 35, 183–199.CrossRefGoogle Scholar
  62. Vassiliou, M.S., 1984. The state of stress in subducting slabs as revealed by earthquakes analysed by moment temsor inversion, Earth Planet. Sci. Lett., 69, 195–202.CrossRefGoogle Scholar
  63. Vassiliou, M.S. and B.H. Hager, 1988. Subduction zone earthquakes and stress in slabs, PAGEOPH, 128, 547–624.CrossRefGoogle Scholar
  64. Weinstein, S.A. and P.L. Olson, 1989. The proximity of hotspots to convergent and divergent plate boundaries, Geophys. Res. Lett., 16, 433–436.CrossRefGoogle Scholar
  65. Weis, D. and F.A. Frey, 1990. 115 Ma of activity of the Kerguelen hotspot in the Indian Ocean (abstract), EOS Trans. AGU, 71, 657.Google Scholar
  66. White, R.S. and D.P. McKenzie, 1989. Magmatism at rift zones: The generation of volcanic continental margins and flood basalts, J. Geophys. Res., 94, 7685–7729.CrossRefGoogle Scholar
  67. Wilson, J.T., 1963. A possible origin of the Hawaiian Islands, Can. J. Phys., 41, 863–868.CrossRefGoogle Scholar
  68. Wilson, J.T., 1965. Evidence from ocean islands suggesting movement in the earth, Roy. Soc. London, Phil. Trans., 258, 145–165.CrossRefGoogle Scholar
  69. Zindler, A. and S. Hart, 1986. Chemical geodynamics, Ann. Rev. Earth Planet. Sci., 14, 493–571.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1991

Authors and Affiliations

  • Mark A. Richards
    • 1
  1. 1.Department of Geology and GeophysicsUniversity of CaliforniaBerkeleyUSA

Personalised recommendations