CRR 1000+ implications of geobarometry from kimberlitic xenoliths
- From: Krubozumo Nyankoye <libvet@xxxxxxxxxx>
- Date: Tue, 02 May 2006 04:59:58 -0000
Alan Johnson <afjohnson@xxxxxxxxxxxxxxxxxx> eyed the audience and in
choked emotion intoned: news:e3052d$oi0$02$1@xxxxxxxxxxxxxxxxx:
Washington, DC. To truly understand some of the movement we see at theExcellent post,
Earth?s surface, scientists have to probe deep into the interior. A
region near the planet?s core, about 1,800 miles down called the
core-mantle boundary, is particularly intriguing. Through novel
experiments mimicking high-pressures and temperatures there,
scientists at Los Alamos National Laboratory (LANL) and the Carnegie
Institution?s Geophysical Laboratory* may have solved a longstanding
mystery about why certain seismic waves called shear waves move so
sluggishly through clumpy patches (ultralow velocity zones) at these
incredible depths. The team found that when lots of iron is added to
the most prevalent mineral in that region (post-perovskite), shear
waves move in slow motion. Their discovery offers an alternative to
the prevailing idea that these regions are partially melted, and it
has important implications for understanding how volcanoes, located in
places such as Hawaii and Iceland, may originate. The research is
published in the April 28, 2006, issue of Science.
Seismologists learn about the deep Earth, in part, by observing
different seismic waves from earthquakes as they travel through the
planet. Shear waves wiggle at right angles to the direction of their
movement, but they don?t move through liquid at all and are thus
useful for understanding aspects of the Earth?s composition. The team,
including the daughter/father duo Wendy Mao (LANL) and Carnegie?s
Ho-kwang (Dave) Mao, used a novel technique to measure the velocity of
shear waves in the lab, moving through the most abundant mineral in
that region (post-perosvkite).
"The major mineral in Earth?s mantle is iron-magnesium silicate
perosvkite," explained Dave Mao. "Post-perosvkite, discovered a couple
years ago, is a different phase of the mineral at the core-mantle
boundary and scientists have been fascinated by its properties.
Understanding the mineral and the intrigue of the ultralow velocity
zones led us to these experiments," he continued.
Ultralow velocity zones exist as patches between the solid mantle and
liquid core, and are very different from the mantle above and material
on the sides. Since shear waves can?t propagate through a liquid, a
prevailing view has been that the zone contains some liquid, or melts,
which would slow the waves down. Scientists have noticed that the
ultralow velocity patches could also give rise to mantle plumes,
eventually sparking volcanoes in places like Hawaii and Iceland.
The researchers subjected post-perosvkite, containing 40% iron, to
pressures as high as 1.6 million times the pressure at sea level (170
Gigapascals) and 3,100 °F (2,000K). Although the researchers can add
as much as 80% iron in the post-perovskite, only 40% is needed to
match the ultralow velocity zones.
"With our new techniques we were able to determine the shear velocity
of this material," stated Wendy Mao. "We were amazed that adding iron
dramatically slowed the velocities to levels that seismologists have
observed in the ultralow velocity zones. Iron-rich post-perosvkite,
formed by reactions between the mantle and the core, could be what
these thin, patchy regions are made of."
In addition to offering an alternative explanation to partial melting
of the ultralow velocity zones, the dense material would sink instead
of rising with the convection at hot spots. This behavior would
explain why these zones are clumped and not uniformly distributed and
why the clumps are associated with the hot spots and contribute to the
volcanic activity at the surface.
-----------------------------------------------------------------------
-------
* Wendy Mao is with Los Alamos National Laboratory. Ho-Kwang (Dave)
Mao is with Carnegie?s Geophysical Laboratory and HPCAT. Yingwei Fei
and Russell Hemley are also with Carnegie.
This work was supported by Earth Sciences Research and the National
Science Foundation. The HPCAT facility is supported by the Department
of Energy, the W. M. Keck Foundation, and Carnegie Institution of
Washington.
The Carnegie Institution of Washington (www.carnegieinstitution.org)
has been a pioneering force in basic scientific research since 1902.
It is a private, nonprofit organization with six research departments
throughout the U.S. Carnegie scientists are leaders in plant biology,
developmental biology, astronomy, materials science, global ecology,
and Earth and planetary science.
__________
Regards
Alan
Two comments:
The CRR is assigned in a subjective fashion based on only a cursory reading
of the tripe from findlay and oriel. A quantitative analysis might indeed
come out much higher, btw, CRR = crackpot reply rating. A pair of wishful
dreamers tackling a concept which they do not even address with pet ideas
whose foundational principles are irrational? Its a pity this news group is
so dominated by these perverse personalities. It was a good forum once
where serious people who actually did serious work could discuss and
advance their overall understanding. Now the only feedback that shows up is
the grandstanding of the snakeoil salesmen. I guess that is what happens
when we tire of refuting the nonsensical. Pity.
Second comment
The implications of this work are interesting to be sure, however, it is
not presented in a context that relates to the known properties and
chemistries of ultra-deep diamonds and xenoliths from kimberlites as
reported by Haggerty and others. To the best of my knowledge, the
geobarometry of ultradeep diamond and xenoliths only goes to depths of ~500
km. To the best of my knowledge, the isotopic compositions of matrix magmas
that transported said xeonliths to the surface are not strictly meteoritic
although they are more closely akin to them than any other rocks. So, even
if we assume that the core mantle boundary is possessed of these anomalous
regions of different phase, how can that be specifically correlated to the
very deep sources of xenoliths, mid ocean volcanic plumes do not produce
such xenoliths, hence one has to wonder, if there is a correspondence
between the core-mantle anomalies and 'plumes' why is there no similar
correspondence between the anomalies and the sources of ultradeep
xenoliths?
Crackpot discussion will be ignored.
Ciao,
--
Here we may reign secure, and in my choyce
To reign is worth ambition though in Hell:
Better to reign in Hell, than serve in Heav'n.
.
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