Re: Scripps/UCSD geophysicist among international team finding evidence of first plate tectonics

On Thu, 22 Mar 2007 16:43:27 -0400, "George" <george@xxxxxxxxxxxxxxx>
wrote:

DF? Response?

http://www.eurekalert.org/pub_releases/2007-03/uoc--sga032207.php

Observations indicate that plate tectonics began before any currently known
structural geological record on Earth
Identification of the oldest preserved pieces of Earth's crust in southern
Greenland has provided evidence of active plate tectonics as early as 3.8
billion years ago, according to a report by an international team of
geoscientists in the March 23 edition of Science magazine.

The finding pushes back the date of continent-forming processes previously
determined as 2.5 billion years ago to a much earlier era considerably
closer to Earth's formation some 4.5 billion years ago. Geochemical
analysis of rocks has previously suggested an earlier date for plate
tectonics, but this is the first study to find physical evidence of
tectonics among Earth's oldest known rock structures, according to Hubert
Staudigel of Scripps Institution of Oceanography at UC San Diego.

"The fact that this rock structure is so well preserved is particularly
lucky," Staudigel said. "The materials were formed as seafloor along a
spreading center and accreted to a continental plate and just stuck there,
surviving almost unscathed for as long as 3.8 billion years."

The study focuses on an area near the southwestern coast of Greenland where
there is a rare outcrop of ancient rock, called the Isua Supracrustal Belt,
which have been dated at 3.8 billion years old. The Isua rocks are
ophiolites, which have a green hue from the chlorite minerals within them
and are found in all major mountain belts, usually located in areas
associated with volcanism and plate tectonics. The Isua deposits were first
described in the 1960s. They also have been found to contain fossilized
evidence of the earliest bacterial life on Earth, also about 3.8 billion
years old, in studies conducted in 1999 by Minik Rosing.

The new study reveals the geological structure at Isua contains both
seafloor pillow lavas and dikes, or sheets, of basalt that intruded into
the pillow lavas after they formed. These features and the chemistry of the
ophiolites indicate that the area was formed as the result of seafloor
spreading, according to lead author Furnes. Even though the rocks have
physically changed over time, it is still possible to see their original
characteristics because of the preservation of fine-grained crystals that
show they were cooled by contact with surrounding colder rocks, Furnes
said.

"To what extent one is able to see an original structure in a highly
deformed rock depends basically on the experience of the observer," Furnes
said. "In our case we knew what we were looking for, and all of us who did
the field work have reasonably good experience with identifying pillow
lavas and associated dikes."

The finding of ophiolites in the oldest known rock structures leads the
scientists to believe that such rocks have formed throughout Earth's nearly
4.5 billion year history, according to de Wit.

There is not enough energy in spreading or subduction to push, or pull
the slab, it is only when the slab turns that gravity gives enough
energy.

Which mean ophiolites could NOT be the product of convection.




"Our work shows that some form of seafloor spreading and oceanic crust
formation occurs as far back in history as geological records go," de Wit
said.

(oh, wait. According to EE, there is no oceanic crust older than 250
million years. Oops. O gues they are proven wrong, yet again!)

Anything to keep your cherished belief alive. It is deep ocean crust.
Ophiolites show uplifting from shallow seas.

But you do have to love this quote, "To what extent one is able to see
an original structure in a highly deformed rock depends basically on
the experience of the observer,"

In essence, seeing what they want to believe.

JT
.