[extropy-chat] Volcanic diamond eruptions

[Robert Bradbury]

On 9/18/06, John K Clark <jonkc at att.net> wrote:

> I realize that, I also realize that if the volcano didn't transport the
> diamonds from very deep in the earth to the surface much more rapidly than
> normal volcanoes the diamond would be turned into graphite.  I can see no
> way such a incredibly explosive event would result in a "small volcano". I
> still don't get it.
>
>
I think the key phrase from the article is "When a kimberlite pipe is
emplaced, the surface expression is that of a small explosive volcanic
eruption consisting of fragments and hot gases (pyroclastic). This volcanic
explosion results in the formation of a small volcanic edifice consisting of
a crater (Maar) and a pyroclastic (tuff) ring. Kimberlite volcanoes have not
been documented mostly because they tend to be small in size and are easily
eroded."

It could have been a "large" volcano but one which eroded relatively
quickly.  Most volcanoes we are aware of today are *very* young in
geological terms.  You also have to deal with the size of the fracture
through which  the pipe is forming.  If it doesn't open up the final volume
of the volcano will be constrained (at the point at which the strength of
the cooling surface material balances the subsurface pressure).  The large
traps are not good examples as they most likely involved very large
fractures representing the release of large amounts of material over long
periods of time (presumably allowing the decay of any diamonds).  All
releases of subsurface material do not result in "volcanoes" as evidenced by
deep sea vents.  It is a complex interaction between the area through which
the surface is being accessed and the composition of the material being
thrust to the surface (in terms of rock and gas composition).  I am
reasonably sure the composition and timing has to be such that contact of
the diamond with oxygen has to be minimized.  I believe that diamond will
oxidize (burn) at temperatures above 800 deg. C resulting in CO2.  As the
temperatures of most magmas is significantly above that it may be true that
a significant fraction of diamonds are being completely vaporized in typical
surface volcanoes.  An open question might also be the conditions under
which C + 2H2O --> 2H2 + CO2.  So bringing diamond to the surface might have
to worry not only about exposure to oxygen but exposure to water.

An interesting question in my mind would be why one doesn't find diamonds in
rapidly upthrust rocks subjected to rapid erosion to remove the surface
material (say the Himalayas)?  Perhaps they are there but still many km
beneath the surface due to the erosion requirements.

The fact that I did find interesting that I was unaware of was the
metastable state of diamond and that it will revert to graphite.  I'd be
interested in knowing the conditions that determine when that happens and
whether it limits the longevity of diamondoid nanostructures.

Robert
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