Nav: Home

SLU geologists discover how a tectonic plate sank

November 14, 2016

ST. LOUIS -- In a paper published in Proceedings of the National Academy of Sciences (PNAS) Saint Louis University researchers report new information about conditions that can cause the earth's tectonic plates to sink into the earth.

John Encarnacion, Ph.D., professor of earth and atmospheric sciences at SLU, and Timothy Keenan, a graduate student, are experts in tectonics and hard rock geology, and use geochemistry and geochronology coupled with field observations to study tectonic plate movement.

"A plate, by definition, has a rigidity to it. It is stiff and behaves as a unit. We are on the North American Plate and so we're moving roughly westward together about an inch a year," Encarnacion said. "But when I think about what causes most plates to move, I think about a wet towel in a pool. Most plates are moving because they are sinking into the Earth like a towel laid down on a pool will start to sink dragging the rest of the towel down into the water."

Plates move, on average, an inch or two a year. The fastest plate moves at about four inches a year and the slowest isn't moving much at all. Plate motions are the main cause of earthquakes, and seismologists and geologists study the details of plate motions to make more accurate predictions of their likelihood.

"Whenever scientists can show how something that is unexpected might have actually happened, it helps to paint a more accurate picture of how the Earth behaves," Encarnacion said. "And a more accurate picture of large-scale Earth processes can help us better understand earthquakes and volcanoes, as well as the origin and locations of mineral deposits, many of which are the effects and products of large-scale plate motions."

Plate movement affects our lives in other ways, too: It recently was reported that Australia needs to redraw its maps due to plate motion. Australia is moving relatively quickly northwards, and so over many decades it has traveled several feet, causing GPS locations to be significantly misaligned.

Subduction, the process by which tectonic plates sink into the earth's mantle, is a fundamental tectonic process on earth, and yet the question of where and how new subduction zones form remains a matter of debate. Subduction is the main reason tectonic plates move.

The SLU geologists' research takes them out into the field to study rocks and sample them before taking them back to the lab to be studied in more detail.

Their work involves geological mapping: looking at rocks, identifying them, plotting them on a map and figuring out how they formed and what has happened to them after they form. Researchers date rock samples and look at their chemistry to learn about the specific conditions where an ancient rock formed, such as if a volcanic rock formed in a volcanic island like Hawaii or on the deep ocean floor.

In this study, Keenan and Encarnacion traveled to the Philippines to study plates in that region. They found that a divergent plate boundary, where two plates move apart, was forcefully and rapidly turned into a convergent boundary where one plate eventually began subducting.

This is surprising because although the plate material at a divergent boundary is weak, it is also buoyant and resists subduction. The research findings suggest that buoyant but weak plate material at a divergent boundary can be forced to converge until eventually older and denser plate material enters the nascent subduction zone, which then becomes self-sustaining.

"We think that the subduction zone we studied was actually forced to start because of the collision of India with Asia. India was once separated from Asia, but it slowly drifted northwards eventually colliding with Asia. The collision pushed out large chunks of Asia to the southeast. That push, we think, pushed all the way out into the ocean and triggered the start of a new subduction zone."

Their finding supports a new model for how plates can begin to sink: "Places where plates move apart can be pushed together to start subduction."

The SLU researchers now want to learn if their model applies to other tectonic plates.

"How common was this forced initiation of a subduction zone that we think happened in the Philippines?" Encarnacion said. "I would like to see work on other ancient subduction zones to see whether our model applies to them as well."
-end-
Other researchers on the study include Robert Buchwaldt, Dan Fernandez, James Mattinson, Christine Rasoazanamparany, and P. Benjamin Luetkemeyer.

Saint Louis University's Department of Earth and Atmospheric Sciences, combines strong classroom and field-based instruction with internationally recognized research across a broad spectrum of the physical sciences, including seismology, hydrology, geochemistry, meteorology, environmental science, and the study of modern and ancient climate change. Students also have the opportunity to work directly with faculty on their research and pursue internships through a growing network of contacts in the public and private sector.

Research centers include the Earthquake Center, the Cooperative Institute for Precipitation Systems, the Global Geodynamics Program, the Center for Environmental Sciences, and Quantum WeatherTM. The fusion of academic programs with world-class research provides students with an unparalleled opportunity to explore their interests and prepare for a wide variety of careers after graduation.

Saint Louis University

Related Tectonic Plates Articles:

Citizen scientists help geologists to identify earthquakes and tectonic tremors
A new study shows that citizen scientists can help professionals in identifying seismic events.
A new idea on how Earth's outer shell first broke into tectonic plates
Plate tectonics theory posits that Earth's outer shell is subdivided into plates that move relative to each other, concentrating most activity along the boundaries between plates, yet the scientific community has no firm concept on how plate tectonics got started.
Why the Victoria Plate in Africa rotates
The East African Rift System is a newly forming plate tectonic boundary at which the African continent is being separated into several plates.
New discovery could highlight areas where earthquakes are less likely to occur
Scientists from Cardiff University have discovered specific conditions that occur along the ocean floor where two tectonic plates are more likely to slowly creep past one another as opposed to drastically slipping and creating catastrophic earthquakes.
Yale finds a (much) earlier birth date for tectonic plates
Yale geophysicists reported that Earth's ever-shifting, underground network of tectonic plates was firmly in place more than 4 billion years ago -- at least a billion years earlier than scientists generally thought.
Research reveals possibly active tectonic system on the Moon
Strange spots scattered across the Moon's nearside where bedrock is conspicuously exposed are evidence of seismic activity set in motion 4.3 billion years ago that could be ongoing today, the researchers say.
Tectonic plates started shifting earlier than previously thought
Scientists examining rocks older than 3 billion years discovered that the Earth's tectonic plates move around today much as they did between 2 and 4 billion years ago.
Researchers discover a new, young volcano in the Pacific
Researchers from Tohoku University have discovered a new petit-spot volcano at the oldest section of the Pacific Plate.
What makes the Earth's surface move?
Do tectonic plates move because of motion in the Earth's mantle, or is the mantle driven by the plates' movement?
Istanbul: Seafloor study proves earthquake risk for the first time
Istanbul is located in close proximity to the North Anatolian fault, a boundary between two major tectonic plates where devastating earthquakes occur frequently.
More Tectonic Plates News and Tectonic Plates Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.