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/

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

'On-off switch' brings researchers a step closer to potential HIV vaccine

30.03.2017 | Health and Medicine

Penn studies find promise for innovations in liquid biopsies

30.03.2017 | Health and Medicine

An LED-based device for imaging radiation induced skin damage

30.03.2017 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>