Re: Evidence from Hawaiian volcanoes shows that Earth recycles its crust

If it is already dissassociated to calcium, there is no way to tell its origin. one Ca++ looks like any other Ca++. If there still are chunks of the original rock (xenoliths) of limestone or dolostone, I'm not sure, because I don't know how extreme heat might affect the isotopic oxygen signatures. Does heavier oxygen offgas at a different rate than lighter oxygen? Dunno.

This fellow isn't the first to come up with the idea that some magma originates in the lower crust. Too bad most of the article contains assertions, not data.




George wrote:
"Paul" <pjw29@xxxxxxxx> wrote in message news:1164883714.927181.106160@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
As a general thought from this article, would the Calcium be viable to
trace it to its original lithology - Limestone, Dolomite etc and use
oxygen isotopes to date such a lithology?

Contact: Carl Blesch
cblesch@xxxxxxxxxxxxxx

Hope this helps. Good question.

George

George wrote:
http://www.eurekalert.org/pub_releases/2006-11/rtsu-efh112706.php

NEW BRUNSWICK/PISCATAWAY, N.J. - A geologist at Rutgers, The State
University of New Jersey, has come up with evidence our planet practices
recycling on a grand scale.

Writing in the prestigious British science journal Nature, geological
sciences professor Claude Herzberg offers new evidence that parts of the
Earth's crust that long ago dove hundreds or thousands of kilometers into
the Earth's interior have resurfaced in the hot lava flow of Hawaiian
volcanoes.

"This concept has been a big issue in the earth sciences," Herzberg said.
While it had been proposed earlier by some geologists, the profession hasn't
embraced it because evidence until now remained sketchy. "Many geologists
felt that when Earth's crust was forced deep into the mantle, a process
called subduction, it would simply stay there."

Herzberg claims to have found telltale chemical evidence at Mauna Kea that
pieces of this submerged crust have been forced up through plumes and now
make up most of this volcano's lava flow. "The low calcium in the Hawaiian
magma pegs it as crust that had melted and been forced to the surface," he
said. The calcium levels in traditional magma, which comes from melting the
Earth's mantle layer below the crust, are much higher.

Herzberg said his research doesn't stop in Hawaii and that his chemical
findings will be useful in understanding the makeup and action of other
volcanoes around the world. These findings extend beyond calcium and
include sulfur, along with isotopes of the heavier elements hafnium and
lead that are tracers for clays and other materials that originated close
to the surface prior to subduction.

"Chemical patterns we've found elsewhere used to be puzzles but are now
starting to make sense," he said.

Still, the big island of Hawaii remains the prime site for uncovering the
secrets of volcanic action, as it has the largest volcanoes on Earth and is
the most productive in terms of lava outpouring. Herzberg believes the
information he's uncovered about magma chemistry might one day help
scientists predict eruptions, as different chemical abundances show up at
different times in the volcanoes' eruption cycles.


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