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The Myth of Whole Mantle Convection JUDGE FOR YOURSELF Don L. Anderson Slide 2 http://www.mantleplumes.org/Penrose/BookChapterPD Fs/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. Slide 3 Ritsema, J., Global seismic maps, Web supplement, 2005. (http://www.mantleplumes.org/TopPages/TheP3Book.html)http://www.mantleplumes.org/TopPages/TheP3Book.html Ritsema, J., van Heijst, H. J., and Woodhouse, J. H., Complex shearwave velocity structure imaged beneath Africa and Iceland, Science, 286, 19251928, 1999. References Slide 4 Evidence for whole mantle convection Visual impression of a few color-saturated tomographic cross- sections Slide 5 Images that suggest whole mantle convection Slide 6 Images that suggest slab flattening Slide 7 The transition zone is a crust-slab-water filter but it filters from above, not below Upper mantle 1000-km Mesosphere Abyss D D LOWERMANTLELOWERMANTLE VISUAL INTERPRETATIONS ARE NOT ALWAYS THE BEST, BUT.... Slide 8 It is now well established that oceanic plates sink into the lower mantle at subduction zones Slide 9 Ritsema, 2005 Slide 10 Transition Zone thickness is independent of hotspot and megaplume locations Slide 11 With this color scheme there are no whole mantle slabs Slide 12 Cartoons are used to interpret the images as slabs and plumes Slide 13 References Fukao, Y., Widiyantoro, S., and Obayashi, M., Stagnant slabs in the upper and lower mantle transition region, Rev. Geophy. 28,291323, 2001. Slide 14 Saturated images showing slab-like features Slide 15 Correlations between seismic velocities (solid) and between velocities and densities (dots and dashes) Slide 16 Different color schemes Slide 17 Deep or shallow Iceland? Slide 18 Different views across Iceland