Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Viscous Cycle: Quartz is Key to Plate Tectonics

17.03.2011
Findings offer new approach to understanding movements of continents

More than 40 years ago, pioneering tectonic geophysicist J. Tuzo Wilson published a paper in the journal Nature describing how ocean basins opened and closed along North America's eastern seaboard.

His observations, dubbed "The Wilson Tectonic Cycle," suggested the process occurred many times during Earth's long history, most recently causing the giant supercontinent Pangaea to split into today's seven continents.

Wilson's ideas were central to the so-called Plate Tectonic Revolution, the foundation of contemporary theories for processes underlying mountain-building and earthquakes.

Since his 1967 paper, additional studies have confirmed that large-scale deformation of continents repeatedly occurs in some regions but not others, though the reasons why remain poorly understood.

Now, new findings by Utah State University geophysicist Tony Lowry and colleague Marta Pérez-Gussinyé of Royal Holloway, University of London, shed surprising light on these restless rock cycles.

"It all begins with quartz," says Lowry, who published results of the team's recent study in the March 17 issue of Nature.

The scientists describe a new approach to measuring properties of the deep crust.

It reveals quartz's key role in initiating the churning chain of events that cause Earth's surface to crack, wrinkle, fold and stretch into mountains, plains and valleys.

"If you've ever traveled westward from the Midwest's Great Plains toward the Rocky Mountains, you may have wondered why the flat plains suddenly rise into steep peaks at a particular spot," Lowry says.

"It turns out that the crust beneath the plains has almost no quartz in it, whereas the Rockies are very quartz-rich."

He thinks that those belts of quartz could be the catalyst that sets the mountain-building rock cycle in motion.

"Earthquakes, mountain-building and other expressions of continental tectonics depend on how rocks flow in response to stress," says Lowry.

"We know that tectonics is a response to the effects of gravity, but we know less about rock flow properties and how they change from one location to another."

Wilson's theories provide an important clue, Lowry says, as scientists have long observed that mountain belts and rift zones have formed again and again at the same locations over long periods of time.

But why?

"Over the last few decades, we've learned that high temperatures, water and abundant quartz are all critical factors in making rocks flow more easily," Lowry says. "Until now, we haven't had the tools to measure these factors and answer long-standing questions."

Since 2002, the National Science Foundation (NSF)-funded Earthscope Transportable Array of seismic stations across the western United States has provided remote sensing data about the continent's rock properties.

"We've combined Earthscope data with other geophysical measurements of gravity and surface heat flow in an entirely new way, one that allows us to separate the effects of temperature, water and quartz in the crust," Lowry says.

Earthscope measurements enabled the team to estimate the thickness, along with the seismic velocity ratio, of continental crust in the American West.

"This intriguing study provides new insights into the processes driving large-scale continental deformation and dynamics," says Greg Anderson, NSF program director for EarthScope. "These are key to understanding the assembly and evolution of continents."

Seismic velocity describes how quickly sound waves and shear waves travel through rock, offering clues to its temperature and composition.

"Seismic velocities are sensitive to both temperature and rock type," Lowry says.

"But if the velocities are combined as a ratio, the temperature dependence drops out. We found that the velocity ratio was especially sensitive to quartz abundance."

Even after separating out the effects of temperature, the scientists found that a low seismic velocity ratio, indicating weak, quartz-rich crust, systematically occurred in the same place as high lower-crustal temperatures modeled independently from surface heat flow.

"That was a surprise," he says. "We think this indicates a feedback cycle, where quartz starts the ball rolling."

If temperature and water are the same, Lowry says, rock flow will focus where the quartz is located because that's the only weak link.

Once the flow starts, the movement of rock carries heat with it and that efficient movement of heat raises temperature, resulting in weakening of crust.

"Rock, when it warms up, is forced to release water that's otherwise chemically bound in crystals," he says.

Water further weakens the crust, which increasingly focuses the deformation in a specific area.

Media Contacts
Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov
Mary-Ann Muffoletto, Utah State University (435) 797-3517 maryann.muffoletto@usu.edu
Related Websites
EarthScope Project: http://www.earthscope.org/
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2010, its budget is about $6.9 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives over 45,000 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.

Cheryl Dybas | EurekAlert!
Further information:
http://www.nsf.gov
http://nsf.gov/news/news_summ.jsp?cntn_id=118951&org=NSF&from=news

More articles from Earth Sciences:

nachricht Mountain glaciers shrinking across the West
23.10.2017 | University of Washington

nachricht Climate change weakens Walker circulation
20.10.2017 | MARUM - Zentrum für Marine Umweltwissenschaften an der Universität Bremen

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Salmonella as a tumour medication

HZI researchers developed a bacterial strain that can be used in cancer therapy

Salmonellae are dangerous pathogens that enter the body via contaminated food and can cause severe infections. But these bacteria are also known to target...

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

3rd Symposium on Driving Simulation

23.10.2017 | Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

 
Latest News

Microfluidics probe 'cholesterol' of the oil industry

23.10.2017 | Life Sciences

Gamma rays will reach beyond the limits of light

23.10.2017 | Physics and Astronomy

The end of pneumonia? New vaccine offers hope

23.10.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>