Multilayer convection? Plumes? ...or Earth rotation?

Fig.1 Gravity and convection ? ..or gravity and rotation?  The question relates to the significance of the concentric structure shown in the tomography (slow wave speeds = red = 'hot-and ductile'; fast wave speeds = 'cold-and-brittle' = blue).  The red colour corresponds mostly to areas underlying the Pacific and the Atlantic. (Global Seismic Maps by J. Ritsema 2005)

There is no doubting the concentric structure in the mantle shown by contoured seismic wave speeds (slow = red, 'hot';  fast = blue, 'cold') (?).  The question is, does the pattern reflect cyclic return of convecting cells to the mantle, just one-off rise ('plumes') both being options in Plate Tectonics.  Or does it reflect Earth rotation (according to Earth expansion)?  To me, symmetry and configuration suggest rotation.

The concentric pattern is superimposed on the patches of red and blue colouration, has a continuous whole-Earth circularity of structure, and lacks definitive verticality suggestive of convective overturn.  An interpretation of plumes may apply for the broad areas of red colour, but suffers from having the most intensely red (fastest /'hottest') colouration at surface, where, if the mantle cools as it rises, it should surely be a paler colour.  Likewise the dense blue zones (='brittle' /cold) that occur deep in the mantle also emphasise circularity of structure, not verticality suggestive of any descending overturn.  There are no zones emphasising verticality that are not cut by the circularity; the dominant structure is concentric (= spin).

One might think that if this circularity of structure is interpreted as reflecting convection it should be restricted to the outer shell of the mantle, not penetrative through it.  Certainly the circularity appears to be the most defined towards the outer parts, but the red colouration should be more restricted to the narrow zone of the ridge, not the entire ocean floor where it is supposedly cooling.

So what are we seeing here?

Convective drag supposedly moves the brittle carapace along at a rate, (it is said) of about 5-10cm in a year.  Compare that with a rotation rate that sees the Earth's surface return to start (a distance of about 80,180km at the equator) in twenty four hours, which is more than 2 million times faster.  Which, we might ask given the transitional discontinuities that seismic wave patterns tell us exist in the crust and the mantle, is the more likely to impart some sort of globally spherical structure that is penetrative through the whole upper mantle, ..and tend to destroy any vestige of verticality that mantle structure might have - regardless of what that verticality represents - convection or otherwise?

My money's on rotation, particularly when the architectural configuration of crustal dislocation virtually defines it. There is certainly no clearly definined up-or-down- pattern of structure (that could be construed as convection) that has escaped the penetrative concentricity that seems, on the face of it at least, to relate to the rotation of the Earth, which, in terms of geological time, is spinning faster than a top.

Read what Don Anderson has to say on convection?
 

 

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