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

Ah you got me there Kimmer and a great chance for a scholarly debate. I do wonder where all that high silica tephra is coming from as there should not be any in the mantle. But there shouldn't be any there anyway if everything is mantle derived. Interesting geological situation as it does not cleanly fit what we know about "magma-ography". While some call it a "plume" it doesn't easily fit the mantle plume signature. The reasoning that it is due to a mantle plume feeding the complex has been largely discarded on several fronts.( in my circles anyway) Some seem to think that seafloor spreading is sufficient to explain the geology of Iceland. Then again surface age is what?-- 3-8 million years old? Maybe we are seeing the kick-off phase of plume upwelling and Iceland will eventually become a long slender island challenging Greenland in size when the Atlantic is twice the size of the pacific in 100 million years. Plumes seem to exist for very long times. It makes sense as they are truly moving a less than a snail's pace.

Abstract: Stein and Stein 2003
Seafloor heat-flow near Iceland on the
North American side of the Mid-Atlantic
Ridge is comparable to that for oceanic
lithosphere elsewhere, and thus shows no
evidence for significantly higher
temperatures associated with a mantle
plume. Heat-flow is higher on the Eurasian
plate than on the North American plate,
an intriguing asymmetry opposite to that
expected from models in which Iceland
formed over a mantle plume.

Heat-flow has played little role in the debate
about hotspots like Iceland, which are on or
near mid-ocean ridges, for two reasons. The
first is that predictions for heat-flow have not
been offered, because such hotspots are thought
to reflect an interaction between upwelling
plumes and nearby spreading centers (Ito et al.
1996) more complex than at mid-plate hotspots
which are generally attributed to a simpler
(albeit not yet understood) interaction of a
plume with a plate interior. Second, seafloor
near on-ridge hotspots is young, less than
40 Myr old. In young seafloor, measured heat-
flow is significantly lower than expected purely
from conductive cooling of the lithosphere,
because some heat is transported by hydro-
thermal circulation of sea water through the
crust (e.g. Stein and Stein 1994). Hence it was
unclear how to characterize "normal" heat flow
and assess possible perturbations.
Plume models imply that heat-flow should be
above the "normal" in several ways...

There is a lot of low silica (mafic)lava there which erupts with a whimper and flows quietly just like mantle magma should --but where does all that high gas "crustal" magma come from? That stuff that has been messing with air traffic the past couple years. By all we understand, there should be none in normal sea floor spreading. Yes, a true enigma. I don't disagree that something lifted the Icelandic Volcanic Complex from the sea floor. I'll ask my buddies what they think about it the next time I am there.

Eman

--- In geology2@yahoogroups.com, Kim Noyes <kimnoyes@...> wrote:
>
> I beg to differ... there is legitimate scientific debate on this but a mantle plume under Iceland is very much a possibility and explains much about why Iceland is Iceland and not simply just another underwater spreading center.
>
> Kimmer

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