Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Suction and pull drive movement of Earth’s plates, U-M researchers show

04.10.2002


As anyone with a smattering of geological knowledge knows, Earth’s crust is made up of plates that creep over the planet’s surface at a rate of several inches per year. But why do they move the way they do? Even experts have had trouble teasing out the exact mechanisms.



A model developed by University of Michigan researchers and published in the Oct. 4 issue of Science provides a relatively simple explanation.

"It’s been known that slabs (portions of plates that extend down into the Earth) drive convection in Earth’s mantle, and ultimately the motion of the surface plates, but it hasn’t been well established exactly how that happens---the ideas have been fairly vague," says Clinton Conrad, a postdoctoral fellow in the department of geological sciences. "In this paper, we’ve been able to describe more precisely how slabs interact with the plates."


When two plates collide, one is forced down beneath the other into the mantle (the plastic-like layer between Earth’s crust and core that flows under pressure), creating what geologists call a subduction zone. Because subducting slabs are colder and denser than surrounding mantle material, they tend to sink like a lead ball in a vat of molasses.

There are two main ways these sinking slabs might influence plate motion. If a slab is attached to a plate, the slab can directly pull the plate toward the subduction zone. A slab that is not well attached to a plate, on the other hand, can’t pull directly on the plate. Instead, as it sinks, it sets up circulation patterns in the mantle that exert a sort of suction force, drawing nearby plates toward the subduction zone much as floating toys are drawn toward the outlet of a draining bathtub.

To understand the relative importance of slab pull and slab suction forces, Conrad and assistant professor of geological sciences Carolina Lithgow-Bertelloni, with whom he worked on the project, developed models in which: 1) only slab suction was operating; 2) only slab pull was operating; and 3) both slab suction and slab pull were at work. Then they compared the plate motions that would result from each of these scenarios with actual plate motions. The best fit was the model that combined slab pull and slab suction forces.

The model also explained an observation that has baffled geodynamicists for some time. "The way the observation was originally framed was that plates that have continents on them are slow, compared to plates that are only oceanic," says Lithgow-Bertelloni. But the real issue is whether or not the plates have slabs attached, she explains. Overriding plates, which have no slabs, are slower than subducting plates, which have slabs. The explanation? Subducting plates move faster because the pull effect acts directly on them, making them move rapidly toward the subduction zone. Overriding plates are also drawn toward the subduction zone---by the suction effect---but at the same time, the pull effect creates forces in the mantle that counteract that motion. The net effect is that overriding plates move more slowly toward the subduction zone than subducting plates do.

"We’ve been able to explain that the difference in speed occurs because slab pull generates mantle flow that counteracts the motion of the overriding plate," says Lithgow-Bertelloni. "We also found that this effect is only important for slabs in the upper 600 to 700 kilometers of the mantle. Any slabs deeper than 700 kilometers do not contribute to this effect. They’re important for driving flow in the mantle, but they’re not important for the pull."

Nancy Ross-Flanigan | EurekAlert!
Further information:
http://www.geo.lsa.umich.edu/dept/faculty/lithgowbertelloni/index.html
http://pubs.usgs.gov/publications/text/understanding.html
http://www.platetectonics.com/

More articles from Earth Sciences:

nachricht NASA eyes Pineapple Express soaking California
24.02.2017 | NASA/Goddard Space Flight Center

nachricht 'Quartz' crystals at the Earth's core power its magnetic field
23.02.2017 | Tokyo Institute of Technology

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>