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2nd October, 2011
Dear WM, The data published in nearly all the petrology/
geochemistry papers on basaltic rocks can be explained
without invoking any thermal anomaly. The presence of
mantle plumes is not necessary and, in many cases, it
is in disagreement with the investigated phenomenology.
An example is the
recent
paper published in G3 by Beier et al. on
Louisville seamounts. The authors state, "Unlike
Hawaiian volcanoes, Louisville volcanoes appear not to
pass through a sequence of evolutionary stages characterized
by older tholeiitic basalts overlain by incompatible
element enriched alkalic and silica-undersaturated lavas.".
Moreover, they state "The youngest
lavas from a given Louisville seamount tend to have the
least enriched incompatible element compositions." They
interpret these features (in contrast with the plume
theory) in the following way: "This unusual chemical
evolution may be the result of re-melting of heterogeneous
hot spot mantle that was partially depleted during the
earlier, age progressive stages." These are ad
hoc solutions. Interestingly, the authors say "Large
fracture zones apparently had no significant effects
on the composition of Louisville magmatism." even
though the Louisville seamount chain is parallel to the
large Heezen and Tharp fracture zones. The authors continue: "magmatism
at several Louisville volcanoes took place over a protracted
period of time, with temporal chemical variations among
the lavas erupted on a particular seamount.". The
igneous activity on each seamount seems to last from
10 to 23 Ma, much longer than other typical Pacific seamounts.
Similarly, igneous activity on some Canary islands lasted
for more than 60 Ma and, despite this, it has been considered
as evidence for a fixed mantle plume impinging beneath
the NE Atlantic lithosphere. It seems not to matter what
is observed–plumes survive anything.–Michele
Lustrino
6th October, 2011
Dear WM, The papers Zhao et al., Origin of the Changbai
intraplate volcanism in Northeast
China: Evidence from seismic
tomography, Chinese Science Bulletin, 49 ,1401-1408,
2004, and Wortel & Spakman, Subduction and Slab Detachment in the Mediterranean-Carpathian
Region, Science, 290, 1910-1917,
2000, along with various of Marjorie Wilson's, justify the
statement "all
the volcanoes in Europe, North Africa and China that have previously been attributed
to plumes are now recognized as natural results of plate tectonics." These
areas are similar to Yellowstone-CRB in that enormous volumes of oceanic crust
and plate have been shoved under these regions.–Don Anderson
26th June, 2011
Dear WM, The recent paper by Christoffersson
& Husebye (2011) shows that
ACH tomography does not work. This is confirmed by
the recent work at Hawaii by Cao
et al. (2011), who show that the structures
formerly claimed to exist beneath Hawaii on the basis
of ACH do not exist after all.–Don Anderson
3rd June, 2011
Dear WM, The recent
paper in Science by Cao
et al. (2011) destroys the
previous Science papers that "proved" the
existence of a plumes under Hawaii, by authors such
as Wolfe and Montelli.
It confirms results published in an old and excellent
paper by Katzman
et al. (1998), which uses a more data and advanced
theory and comes to an opposite interpretation of the
final results. Katzman
et al. (1998) use a lot more than just SS and
also allow for anisotropy.
The "hot-megablob" 2000 km W of Hawaii
is one of many in the Pacific that have nothing to
do with "plumes" or
particularly hot mantle. There are lots of places in
the world, Pasadena is one, with thinner (hotter) transition
regions.
I encourage you to read the attached and compare
it with the recent Science paper.–Don Anderson
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