[Geology2] Re: Volcano Activity - Iceland ...Not due to a "mantle plume"

Yes indeed some of the "meta-basalt" that is exposed at various points along the TN/NC/GA border was one of the clues that got folks to thinking about it but most of it is older than the early Cretaceous. Paleo seismic findings led to estimating the path under the southeastern US. The original plume may have started at the close of the Triassic.

Why we did not see more evidence on the surface we don't know other than that the plume began under a continental craton with very deep basement rocks which spread the magma out like butter on the underside of the North American Plate.

Note that a "hot spot" is not the same as a mantle plume although they must be from a related geophysical process. Plumes originate deep in the mantle several hundreds of kilometers while "hot spots" seem to come from the crust mantle boundary. The Yellowstone Complex can be followed from near the plate margins to its current location in Wyoming as some of the magma did break surface from time to time. As the slab pull on the Pacific plate is down and under to the east it would be going in the wrong direction for a plume to be the sole cause.

The wonderful thing about modern mineralogy and petrology makes it easy to prove the magma's origins and to observe changes over millions of years and countless eruptions. This is how we know from where the magma comes from. The silica rich, extrusive deposits aka ash which covered 1/3 of the present day US and the known eruption history of those massive ash deposits tells us that the magma was derived from almost completely from the crust.

Eman
--- In geology2@yahoogroups.com, Lin Kerns <linkerns@...> wrote:
>
> Well. That theory would go a long way in explaining why the Unaka Mountains
> that border a small area on the Northeastern tip of the Smoky Mountains in
> Tennessee have highly metamorphosed mafic lava.
>
> Much to consider.
>
> Lin

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