Nature 350, 55 - 57 (07 March 1991); doi:10.1038/350055a0

Intermittent layered convection in a model mantle with an endothermic phase change at 670 km

Philippe Machetel  & Patrice Weber

UPR 234/CNRS/GRGS 18 avenue E. Belin, 31055 Toulouse, France

IT is not yet known whether convection in the Earth's mantle occurs in cells that extend throughout the entire depth of the mantle, or if the upper and lower mantle convect in independent layers; both possibilities seem to be consistent with geochemical and seismologi-cal observations^1-4. It is generally accepted, however, that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change, spinel perovskite + MgO. Here we investigate the results of including this phase change in a model of mantle convection. For realism and to eliminate scaling problems, our calculations use commonly accepted values of geophysical parameters. For a Clapeyron slope y = -2 10⁶, a value close to experimental results and theoretical expectations, we observe local intermittent mixing between the upper and lower mantle. Such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole-mantle and layered convection.

References

1.	Dupré, B. & Allègre, C. J. Nature 303, 142−146 (1983). | Article | ISI | ChemPort |
2.	Allègre, C. J., Hart, S. R. & Minster, J. F. Earth planet. Sci. Lett. 66, 177−190 (1983). | Article |
3.	Olson, P., Carlson, P. G. & Carlson, R. W. Nature 344, 209−214 (1990). | Article | ISI |
4.	Jeanloz, R. & Morris, S. A. Rev. Earth planet. Sci. 14, 377−415 (1986).
5.	Christensen, U. R. & Yuen, D. A. J. geophys. Res. 89, 4389−4402 (1984). | ChemPort |
6.	Christensen, U. R. & Yuen, D. A. J. geophys. Res. 90, 10291−10300 (1985).
7.	Machetel, P. Geophys. Res. Lett. 17, 1145−1148 (1990).
8.	Boehler, R. & Chopelas, A. Geophys. Res. Lett. (submitted)
9.	Ito, E. & Katsura, T. Geophys. Res. Lett. 16, 425−428 (1989). | ISI | ChemPort |
10.	Ito, E. & Takahashi, E. J. geophys. Res. 94, 10637−10646 (1989). | ISI |
11.	Price, G. D., Wall, A. & Parker, S. C. Phil. Trans. R. Soc. A 328, 391−407 (1989). | ChemPort |
12.	Dziewonski, A. M. & Anderson, D. L. Phys. Earth planet. Inter. 25, 297−356 (1981). | Article | ISI |
13.	Machetel, P. & Yuen, D. A. J. geophys. Res. 94, 10609−10626 (1989).
14.	Houseman, G. Nature 332, 346−349 (1988). | Article |
15.	Glatzmaier, G. A., Schubert, G. & Bercovici, D. Nature 347, 274−277 (1990). | Article |
16.	Weinstein, S. & Olson, P. Geophys. Res. Lett. 17, 239−242 (1990).
17.	Dziewonski, A. M. J. geophys. Res. 89, 5929−5952 (1984). | ISI |
18.	Le Pichon, X. & Huchon, P. Earth planet. Sci. Lett. 67, 123−135 (1984). | Article |
19.	Ringwood, A. E. & Irifune, T. Nature 331, 131−136 (1988). | Article | ISI | ChemPort |
20.	Stacey, F. D. Phys. Earth planet. Inter. 15, 341−348 (1977). | Article | ISI |
21.	Anderson, D. L. Theory of the Earth, 366 (Blackwell Scientific, Boston, 1989).
22.	Hager, B. H. & Richards, M. A. Phil. Trans. R. Soc. A 328, 309−327 (1989).
23.	Stacey, F. D. & Loper, D. E. Phys. Earth planet. Inter. 53, 167−174 (1988). | Article | ChemPort |