Contact

Prof. Alexander Sobolev

Max Planck Institute for Chemistry, Mainz

Phone: +49 6131 305-609

Dr. Klaus Peter Jochum

Max Planck Institute for Chemistry, Mainz

Phone: +49 6131 305-216

Dr. Susanne Benner

Max Planck Institute for Chemistry, Mainz

Phone: +49 6131 305-3000
Fax: +49 6131 305-3009

Original publication

Alexander V. Sobolev, Albrecht W. Hofmann, Klaus Peter Jochum, Dmitry V. Kuzmin & Brigitte Stoll
A young source for the Hawaiian plume
Nature, 10 August 2011

Earth Sciences

Deep recycling in the Earth faster than thought

Sunken oceanic crust resurfaces from Earth's mantle after only 500 million years

August 10, 2011

The recycling of the Earth's crust in volcanoes happens much faster than scientists have previously assumed. 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. Researchers from the Max Planck Institute for Chemistry in Mainz obtained this result using volcanic rock samples. Previously, geologists thought this process would take about two billion years.
Olivine crystals from Mauna Loa volcano, Hawaii, with a width of less than one millimeter. The brown ovals are solidified, glassy inclusions trapped as droplets of melt by the growing olivine crystal. They contain strontium isotope ratios which are inherited from 500 million year old seawater. Zoom Image
Olivine crystals from Mauna Loa volcano, Hawaii, with a width of less than one millimeter. The brown ovals are solidified, glassy inclusions trapped as droplets of melt by the growing olivine crystal. They contain strontium isotope ratios which are inherited from 500 million year old seawater. [less]

Virtually all of the ocean islands are volcanoes. Several of them, such as Hawaii, originate from the lowest part of the mantle. This geological process is similar to the movement of coloured liquids in a lava lamp: hot rock rises in cylindrical columns, the so-called mantle plumes, from a depth of nearly 3,000 kilometers. 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.

The microscopically small inclusions in the volcanic rock contain trace elements originally dissolved in seawater, and this allows the recycling process to be dated. Before the old ocean crust sinks into the mantle, it soaks up seawater, which leaves tell-tale trace elements in the rock. The age is revealed by the isotopic ratio of strontium which changes with time. Strontium is a chemical element, which occurs in trace amounts in sea water. The isotopes of chemical elements have the same number of protons but different numbers of neutrons. Mainz scientists developed a special laser mass spectrometry method which allowed the detection of isotopes of strontium in extremely small quantities.

 
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