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Atlantic floor destined to slip under North American continent

An interactive global map of sea floor topography based on satellite altimetry & ship depth soundings
Minneapolis - Oct 22, 2001
It won't happen overnight, but eventually, the floor of the Atlantic Ocean will plunge beneath the North American continent, forming a deep trench about 2,000 miles long and possibly generating volcanoes, according to research at the University of Minnesota and the Swiss Federal Institute of Technology in Zurich.

Formation of the trench will begin in three million to 10 million years and is projected to take about three million years. It will be triggered by water seeping into offshore rock -- built up by river sediments -- and making the rock softer and more pliable. The study will be published in the Oct. 19 issue of Science.

Plates of the Earth's crust slide under other plates in a process known as subduction. Subduction has formed deep trenches in the Pacific Ocean floor and raised mountains around the world, including the string of volcanoes between British Columbia and Oregon.

A similar fate awaits the East Coast, but it will happen on a much larger scale, said author David Yuen, professor of geology and geophysics at the University of Minnesota.

"The West Coast trenches are small because there are numerous small plates there," said Yuen. "That area is called the Cascadian Subduction Zone, and it extends only about 370 miles. But the East Coast zone is 2,000 miles."

Yuen and his colleagues simulated the fate of the offshore sediments along the East Coast, where rivers have been dumping sediment for 100 million years. They found that this has built up layers of sedimentary rock tens of miles thick that presses down on the ocean bottom.

But the critical factor is likely to be seepage of water into the rock, which is quite porous. When water seeps in, it lubricates the rock and makes it softer and less resistant to being deformed or pushed.

The push comes from the middle of the Atlantic, where undersea mountains are rising and exerting pressure on the rock, driving it toward North America.

At some point in the next several million years, the ocean bottom will succumb to the downward and westward pressure and start to slide under the continent. Instead of a gently sloping continental shelf, the coast will develop a deep oceanic trench. And inland volcanoes may rise roughly parallel to the trench.

To perform the simulation, the researchers used equations that describe how water in rock makes it more pliable. David Kohlstedt, also a professor of geology and geophysics at the university, headed the team that derived the equations.

Yuen's colleagues in the study were Klaus Regenauer-Lieb, a research assistant at the Swiss Federal Institute of Technology, and Joy Branlund, who at the time was a graduate student at the University of Minnesota.

"When the oceanic slab begins to slide under the continent, the process will spread up and down the coast like a crack propagating," said Yuen. "That will take about three million years. We used data from East Coast sediments because there are no other places in the world where sediments are loading like that. This model leads to the prediction that geologically, the East Coast will eventually resemble the Pacific Northwest coast."

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Buoyancy Explains How Volcanic Rock Rises Through the Earth's Mantle
Atlanta - August 31, 2001
A new study of the Earth's mantle beneath the ocean near Iceland provides the most convincing evidence yet that simple buoyancy of hot, partially molten rocks can play an important role in causing them to rise and erupt through the surface at mid-ocean ridges.

Revealing Earth's Deepest Secrets
Ann Arbor - Sept. 5, 2001
In work that promises to advance understanding about the origin and dynamics of Earth's iron-rich inner core and the generation of the planet's magnetic field, a team that includes University of Michigan researchers has found that the elastic properties of iron are quite different at extremely high temperatures than at low temperatures.

Earthquakes Reveal Diamonds' Origins
Tempe - July 13, 2001
The seismic rumblings could provide key clues about where miners should look for diamonds, according to recent research. Matt Fouch, assistant professor of geological sciences at ASU, studies vibrations caused by earthquakes to visualize the earth at depths of hundreds of kilometers, where diamonds are formed.

The Moon And Plate Tectonics: Why We Are Alone
Sydney - July 11, 2001
The existence of a large Moon in orbit around the Earth and its implications for the origin and nature of life have been a subject of considerable discussion. With the Hartmann/Davis models for the catastrophic origin of the Moon by glancing collision, it has become clear that our Moon is a rare celestial object and that few Earth-like planets could have produced such a chance outcome during their assembly.

U.Hawai'i Researchers Propose New Geological Formation Theory
Honolulu - July 7, 2001
Throughout geologic history, continents have been pulled apart by tectonic forces forming rifts that eventually become new ocean basins. Sometimes during this process rock layers near the earth's surface are pulled apart and rocks from depths of 35 kilometers or more are exposed at the Earth's surface.



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