Re: Evidence from Hawaiian volcanoes shows that Earth recycles its crust

In article <ClYbh.8669$f8.550@xxxxxxxxxxxxxxxxxxxxxx>, George wrote:
As to your questions, above, if the hotspot theory
is correct, and the plume originates at or near the core-mantle boundary,
and if this report is correct, and much of the magma originates from
previously subducted material, then at least my tentative conclusion would
be that since the CMB has a much smaller radius than the surface of the
Earth, it stands to reason that once the subducted material reaches those
depths, it can theoretically come back up to the surface many thousands of
miles from where it originated, especially if, once arriving at the CMB, it
migrated laterally before being bouyed back up to the surface.

In short, the mantle is reasonably well-stirred.
Which is not completely incompatible with the discovery over the last
decade or so of regional variations in fundamental parameters like original
isotopic ratios for various clock systems. Which imply significant mantle
heterogeneity back at the end of the Late Heavy Bombardment (impact scars ??)
which has not yet been homogenised away. The two ideas are not completely
incompatible, but you do need a moderately precisely small amount of mixing.
As Goldilocks would say "that's just right".

--
Aidan Karley, FGS,
Aberdeen, Scotland
A light wave is more like a crime wave than a water wave.

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