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segunda-feira, 23 de maio de 2011

@BreakingScience The Atlantic 'resting' -- for now

The Atlantic 'resting' -- for now via

http://www.physorg.com/

New oceanic crust forms on the mid-ocean ridge while oceanic crust that has cooled down is swallowed up in subduction zones. (Photo: Jeker Natursteine AG, Berne)

Geophysicists have simulated when the continents around the Atlantic develop active continental margins with earthquakes and volcanoes. According to the model, ‘real’ fully active subduction zones will not form for another twenty million years at the earliest.

Oceanic trenches, earthquakes, mountains and volcanoes arise through the subduction of tectonic plates. These phenomena shape the renowned Pacific Ring of Fire around the Pacific. Along this ring, sinks beneath the continental margins while new oceanic crust is constantly formed on the mid-ocean ridge. The process of subduction sets in once the oceanic crust is several tens of millions of years old and has cooled down to such an extent that it has a higher density than the area of the earth’s mantle beneath it, namely the asthenosphere. Consequently, it sinks beneath the adjacent continent more or less by itself. In the world’s oceans, there is thus hardly any oceanic crust that is older than about 170 million years.

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