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MELT Data Sheds New And Surprising Light On Birth Of Oceanic Plates

Date:
September 14, 2005
Source:
Brown University
Summary:
In the first joint interpretation of data from the landmark MELT study, a team of scientists including Donald Forsyth of Brown University has found unexpected changes in the patterns of seismic velocity and electrical conductivity near the East Pacific Rise, changes due to dehydration and cooling. Results are published in Nature.
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The MELT Project (Mantle Electromagnetic and Tomography): Data from 81 instruments on the seafloor has yielded important new understandings of how the Earth’s crust is formed.
Credit: Image courtesy of Brown University

PROVIDENCE, R.I. — The East Pacific Rise, a vast volcanicmountain range submerged in the eastern Pacific Ocean, is one of thefastest seafloor factories on the planet. Here, along a rocky spinethat runs about 1,000 miles west of South America, oceanic crust iscreated from magma bubbling up from deep within Earth’s interior.

Forcesthat shape these young oceanic plates have come into clearer focusthrough research conducted by scientists at the Woods HoleOceanographic Institution, Brown University and the Japan Agency forMarine-Earth Science and Technology.

The research represents thefirst time that seismic and electromagnetic data were analyzed intandem from 1995 Mantle Electromagnetic and Tomography, or MELT,Experiment. MELT employed 51 ocean-bottom seismometers and 30magnetotelluric receivers two miles under the sea to measure soundwaves and magnetic fields along the East Pacific Rise, making it one ofthe largest marine geophysical experiments ever conducted.

In apaper published in Nature, the team notes that in rock down to a depthof about 60 kilometers below the ocean floor, electrical currentsconduct poorly and sound waves travel rapidly. Deeper down, beyond 60kilometers, there is a dramatic increase in electrical conductivity,and sound waves travel at their slowest.

A switch in seismic andelectrical properties with depth was expected. Researchers weresurprised, however, at how close to the East Pacific Rise thisstructure develops and how little it changes with increasing distancefrom the rise.

Brown marine geophysicist Donald Forsyth said theteam, led by Robert Evans from the Woods Hole OceanographicInstitution, has a theory about the cause of the sudden compositionalchanges at 60 kilometers: dehydration.

As magma migrates to thesurface to form crust at the rise, it leaves behind a dry, residuallayer about 60 kilometers thick. This change from “dry” surface rock to“damp” rock below it increases electrical conductivity and slowsseismic velocity, the researchers write.

Here is what they didnot expect: These changes occur, the team found, less than 100kilometers away from the highest point on the ridge. And the seismicand electrical measurements remained nearly constant at least about 500kilometers away from the crest.

Separating seafloor guides magmaup to mid-ocean ridges such as the East Pacific Rise, where the moltenrock erupts, fans out along the ocean floor and cools to form newcrust. Cooling allows sound waves and electrical currents to travelfaster. But scientists thought this cooling – and the resulting changesin the rock – would be gradual.

“About two-thirds of the Earth’ssurface is oceanic crust – and it is all formed at ridges,” Forsythsaid. “So this work helps us better understand the basic processes ofhow this crust is formed.”

The National Science Foundation funded MELT and the latest research.


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The above post is reprinted from materials provided by Brown University. Note: Materials may be edited for content and length.


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Brown University. "MELT Data Sheds New And Surprising Light On Birth Of Oceanic Plates." ScienceDaily. ScienceDaily, 14 September 2005. <www.sciencedaily.com/releases/2005/09/050909075217.htm>.
Brown University. (2005, September 14). MELT Data Sheds New And Surprising Light On Birth Of Oceanic Plates. ScienceDaily. Retrieved June 29, 2015 from www.sciencedaily.com/releases/2005/09/050909075217.htm
Brown University. "MELT Data Sheds New And Surprising Light On Birth Of Oceanic Plates." ScienceDaily. www.sciencedaily.com/releases/2005/09/050909075217.htm (accessed June 29, 2015).

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