Monday, August 15, 2011

Rapid Recycling of The Earth's Crust

A young source for the Hawaiian plume. 2011. A. V. Sobolev, et al. Nature, Published online Aug. 10.
The recycling of the Earth's crust in volcanoes happens much faster than scientists have previously assumed.

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Rock of the oceanic crust, which sinks deep into the earth due to the movement of tectonic plates, reemerges through volcanic eruptions after around 500 million years. Previously, geologists thought this process would take about two billion years.

Some ocean islands, such as Hawaii, originate from the lowest part of the mantle as hot rock rises in cylindrical columns (mantle plumes), from a depth of nearly 3000 kilometres. Near the surface, it melts, because the pressure is reduced, and forms volcanoes. The plume originates from former ocean crust which early in the Earth's history sank to the bottom of the mantle. Previously, scientists had assumed that this recycling took about two billion years.

The chemical analysis of tiny glassy inclusions in olivine crystals from basaltic lava on Mauna Loa volcano in Hawaii has now surprised geologists: the entire recycling process requires at most half a billion years, four times faster than previously thought. link

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