The Myth of Whole Mantle Convection

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The Myth of Whole Mantle Convection

• JUDGE FOR YOURSELF
• Don L. Anderson

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http//www.mantleplumes.org/Penrose/BookChapterPDF
s/RitsemaWebSuppl_Accepted.pdf

• The large, red, 2000-km-wide feature extends from
  the southern hemisphere under the Shona and
  Bouvet volcanic regions to the Afar region, some
  7000 km distant.
• It has been assumed to be a continuous hot
  feature that penetrates the whole mantle.
  

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References
Ritsema, J., Global seismic maps, Web supplement,
2005. (http//www.mantleplumes.org/TopPages/TheP3B
ook.html) Ritsema, J., van Heijst, H. J., and W
oodhouse, J. H., Complex shearwave velocity
structure imaged beneath Africa and Iceland,
Science, 286, 19251928, 1999.
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Evidence for whole mantle convection

• Visual impression of a few color-saturated
  tomographic cross-sections

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Images that suggest whole mantle convection
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Images that suggest slab flattening
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VISUAL INTERPRETATIONS ARE NOT ALWAYS THE BEST,
BUT....
Upper mantle
Mesosphere
1000-km
LOWER MANTLE
Abyss
D
D
The transition zone is a crust-slab-water filter
but it filters from above, not below
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It is now well established that oceanic plates
sink into the lower mantle at subduction zones
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Ritsema, 2005
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Transition Zone thickness is independent of
hotspot and megaplume locations
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With this color scheme there are no whole mantle
slabs
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Cartoons are used to interpret the images as
slabs and plumes
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References

• Fukao, Y., Widiyantoro, S., and Obayashi, M.,
  Stagnant slabs in the upper and lower mantle
  transition region, Rev. Geophy. 28,291323, 2001.

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Saturated images showing slab-like features
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Correlations between seismic velocities (solid)
and between velocities and densities (dots and
dashes)
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Different color schemes
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Deep or shallow Iceland?
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Different views across Iceland