Good article, thanks for sending it!  I had the pleasure of listening to
Humphreys give a lecture on the same issue and he had some really interesting
views not listed in the article.  

In particular I remember his idea that the huge amount of basalts erupted in
the northwest US may have depleted the upper mantle of iron, which would
cause physical and chemical shifts that would buoy the material upwards to
the surface due to a lower density (less garnet also).  This would in turn
create melt in the same manner as other upwellings through decompression.  If
this idea is correct, then the root of the heat should be very shallow, but
perhaps seismically indistinguishable from pure extension related
volcanism...perhaps an electrical tomography experiment is also in order
here.

John Hernlund
E-mail: hernlund@.......
WWW: http://www.public.asu.edu/~hernlund/

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