Ancient Magma 'Superpiles' May Have Shaped The Continents

[Dover]

Researchers have linked two giant plumes of hot rock deep within the earth to the plate motions that shape the continents. This new drawing of Earth's interior is based on one originally developed by study co-author Louise C. Kellogg of the University of California, Davis and her colleagues in 1999. A giant plume of hot rock called a "superpile" (orange) sits atop Earth's core (red), while the remnants of two subducted continental plates (blue) sink down on either side of it. A magma plume (orange with red outline) can be seen rising from the superpile to the surface as a hotspot that creates island chains such as Hawaii. Image by the Cooperative Institute for Deep Earth Research (CIDER) collaboration, courtesy of Ohio State University.


Ancient Magma 'Superpiles' May Have Shaped The Continents

The two superplumes, one beneath Hawaii and the other beneath Africa, have likely existed for at least 200 million years, explained Wendy Panero, assistant professor of earth sciences at Ohio State University.

The giant plumes -- or "superpiles" as Panero calls them -- rise from the bottom of Earth's mantle, just above our planet's core. Each is larger than the continental United States. And each is surrounded by a wall of plates from Earth's crust that have sunk into the mantle.

She and her colleagues reported their findings at the American Geophysical Union meeting in San Francisco.

Computer models have connected the piles to the sunken former plates, but it's currently unclear which one spawned the other, Panero said. Plates sink into the mantle as part of the normal processes that shape the continents. But which came first, the piles or the plates, the researchers simply do not know.

"Do these superpiles organize plate motions, or do plate motions organize the superpiles? I don't know if it's truly a chicken-or-egg kind of question, but the locations of the two piles do seem to be related to where the continents are today, and where the last supercontinent would have been 200 million years ago," she said.

That supercontinent was Pangea, and its breakup eventually led to the seven continents we know today...cont'd

http://www.physorg.com/news148576119.html


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This image shows a map of the 2007 earthquakes and dyking event in Tanzania. The black circles indicate earthquakes, and the red line shows the location of the dyke intrusion. Purdue University image/Calais laboratory


Team first to record key event that breaks continents apart


An international research team led by Eric Calais, a Purdue University professor of geophysics, was able to measure ground displacements as two tectonic plates in Africa moved apart and molten rock pushed its way toward the surface during the first so-called "dyking event" ever recorded within the planet's continental crust.

The event left a wall of magma 6 miles long and 5 feet wide wedged between the two plates. A paper detailing the event will be published Wednesday (Dec. 11) in Nature.

Dyking events have been reported in the thin oceanic crust but had never been directly observed and quantified in the thicker areas of the planet's shell, Calais said.

"Such dyking events had been included in theories, but researchers had never before been in the right place at the right time with the right equipment to record them," Calais said. "The event was preceded by a slow slipping of the tectonic plates along a fault line. This also had not been seen before. Faults usually slip suddenly, which produces earthquakes, but this was a very seismically quiet course of events that lasted about one week."

The existence of these events provides a key element of how the Earth's rigid outer shell - the lithosphere - breaks apart and moves. The known forces pushing and pulling on continents are not powerful enough to break them apart. However, repeated dyking events could weaken the lithosphere severalfold, allowing it to shift and break under far less force, Calais said.

"To break a continent apart, one needs to overcome the strength of the Earth's lithosphere," he said. "But when we calculate the forces available from plate tectonics, we find that they are not large enough to do the job. We know that continents break apart and have done so repeatedly in the geological past. So, how can it happen? One way is to add a little push to the system, and this is exactly what dyke intrusions do." ..cont'd

http://www.physorg.com/news148136691.html

[OnceUponTimeOnTheNet]

1. The second part of your post fascinates me. Rift.

My region has a failed rift, it really shows up on the Gravity Anomaly Maps.
http://www.geo.umn.edu/mgs/nicegeo/pdfs/boug_grav.pdf
Goes thru Lake Superior and straight down thru Iowa.

[Dover]

2. That IS fascinating!

Have never heard of the Bouguer gravity anomoly. Not sure I understand exactly what that is
and how it relates to the dyking event in Africa, though.