Supercontinent Pangaea pushed, not sucked, into place 300 million years ago

September 6th, 2008 - 4:56 pm ICT by ANI  

National Geographic

Washington, September 6 (ANI): A new study has suggested that supercontinents like Pangaea can form when a huge plume of hot rock from deep inside Earth wells up between the continental plates, pushing them apart until all Earth’’s landmasses collide.
According to a report in National Geographic News, this is the finding from a new study that suggests-contrary to accepted theory-that such a process formed the supercontinent Pangaea 300 million years ago.
Scientists believe that Earth’’s shifting plates have been forming and breaking up supercontinents for billions of years, and traditionally they thought that suction is the driving force.
In seismically active places such as the Ring of Fire in the Pacific region, slabs of Earth’’s crust descend into the interior in a process called subduction.
This creates a downward current that sucks the continents into collision above it, like soapsuds being drawn together as water flows down a drain.
But in the new study, J. Brendan Murphy of St. Francis Xavier University in Nova Scotia, Canada, and colleagues suggest that a plume of subducting crust in the middle of the ancestral Pacific Ocean descended so deeply it hit Earth’’s core.
Superheated, it then rebounded like a bubble in a boiling pot. That produced a superplume strong enough to push, not suck, the ancient continents back together and form Pangaea.
Peter Cawood, director of the Tectonics Special Research Centre at the University of Western Australia, called the finding “excellent and stimulating.”
According to Murphy’’s new study, there’’s something wrong with the suction-driven model in the case of Pangaea.
The problem is that it’’s very clear from the geologic record that the formation of Pangaea from the fragments of Gondwana occurred in two stages.
First, Gondwana split, producing a steadily widening “young” ocean in its heart, much like the Atlantic Ocean that now separates the fragments of Pangaea.
Then something shifted.
Rather than continuing to widen, as it would if its motion was being driven by suction, the new ocean started to shrink. The continents reversed course and slammed back into each other to form Pangaea.
This accordionlike action, dubbed the “Wilson Cycle”, has been recognized for more than 40 years, but the forces responsible for it are unknown.
Moreover, if current models thought to be responsible for these movements were applied to a 500-million-year-old Earth, they would not produce Pangaea in the right configuration.
According to Murphy, why this reversal happened is unclear, and that’’s disconcerting, because even though Pangaea is the best studied of the supercontinents, “something happened that we don”t understand.”
The new theory of a superplume interfering with the suction process could put the pieces of what occurred into place, although more data would be needed to cement the idea. (ANI)

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