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 Scientists shed light on carbon's descent into the deep Earth
19.07.2017 | European Synchrotron Radiation Facility

nachricht Thawing permafrost releases old greenhouse gas
19.07.2017 | GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

Leipzig HTP-Forum discusses "hydrothermal processes" as a key technology for a biobased economy

12.07.2017 | Event News

 
Latest News

Researchers create new technique for manipulating polarization of terahertz radiation

20.07.2017 | Information Technology

High-tech sensing illuminates concrete stress testing

20.07.2017 | Materials Sciences

First direct observation and measurement of ultra-fast moving vortices in superconductors

20.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>