Earth's Moving Crust May Occasionally Stop
January 10, 2008
The motion, formation, and recycling of Earth's crust-commonly known as plate tectonics-have long been thought to be continuous processes. But new research by geophysicists suggests that plate tectonic motions have occasionally stopped in Earth's geologic history, and may do so again. The findings could reshape our understanding of the history and evolution of the Earth's crust and continents.
Synthesizing a wide range of observations and constructing a new theoretical model, researchers Paul Silver of the Carnegie Institution of Washington and Mark Behn of the Woods Hole Oceanographic Institution (WHOI) have found evidence that the process of subduction has effectively stopped at least once in Earth's past. Subduction occurs where two pieces of Earth's crust (tectonic plates) collide, and one dives beneath the other back into the interior of the planet.
Most of the major geologic processes on Earth-the formation of continents, the birth of volcanic island arcs, the opening and closing of ocean basins-are driven by tectonic plate motions and intimately linked to subduction and to seafloor spreading. If those processes were shut down, there would likely be a global decrease in earthquakes and volcanism.
Today, the vast majority of subduction occurs around the edges of the Pacific Ocean, which is slowly closing as the Atlantic Ocean opens. In roughly 350 million years, researchers estimate that the Pacific basin will be effectively closed and a new supercontinent will be formed.
Closure of the Pacific basin could shut down most of the Earth's capacity for subduction, unless the process begins somewhere else on the planet. However, there is no evidence that subduction is currently expanding or initiating anywhere else on the planet.
Though such a shutdown defies the prevailing wisdom about plate tectonics, Silver and Behn read the geologic evidence to suggest that just such a dramatic decrease in subduction happened about one billion years ago, after the formation of the supercontinent Rodinia.
Their findings-captured in a paper entitled "Intermittent Plate Tectonics?"-were published in the January 4 issue of the journal Science.
"The scientific community has typically assumed that plate tectonics is an active and continuous process, that new crust is constantly being formed while old crust is recycled," said Behn, an assistant scientist in the WHOI Department of Geology and Geophysics. "But the evidence suggests that plate tectonics may not be continuous. Plates may move actively at times, then stop or slow down, and then start up again."
Behn and Silver started their investigation by considering how the Earth releases heat from its interior over time, also known as "thermal evolution." If you take the rate at which the Earth is releasing heat from its interior today and project that rate backwards in time, you arrive at impossibly high and unsustainable numbers for the heat and energy contained in the early Earth. Specifically, if the planet has been releasing heat at the modern rate for all of its history, then it would have been covered with a magma ocean as recently as one billion years ago.
But we know this is not true, Behn said, because there is geological evidence for past continents and supercontinents, not to mention rocks (ophiolites) on the edges of old plate boundaries that are more than one billion years old.
The Earth cools more quickly during periods of rapid plate motions, as warm material is pulled upward from deep in the Earth's interior and cools beneath spreading ridges.
"If you stir a cup of coffee, it cools faster," said Behn. "That's why people blow on their coffee to get the surface moving."
"It is a similar process within the Earth," Behn added. "If the tectonic plates are moving, the Earth releases more heat and cools down faster. If you don't have those cracked and moving plates, then heat has to get out by diffusing through the solid rock, which is much slower."
Periods of slow or no subduction would help explain how the Earth still has so much heat to release today, since some of it would have been capped beneath the crust.
Silver and Behn conclude their paper by suggesting that there is a cycle to plate tectonics, with periods when the shifting and sliding of the crust is more active and times when it is less so. Rather than being continuous, plate tectonics may work intermittently through Earth history, turning on and off as the planet remakes itself.
The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.
The Carnegie Institution of Washington has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.
Woods Hole Oceanographic Institution
Related Subduction Current Events and Subduction News ArticlesDeep-Earth Carbon Offers Clues About Origin of Life on Earth
New findings by a Johns Hopkins University-led team reveal long unknown details about carbon deep beneath the Earth's surface and suggest ways this subterranean carbon might have influenced the history of life on the planet.Seismic Hazard in the Puget Lowland, Washington State, USA
Seismic hazards in the Puget Lowland of northwestern Washington include deep earthquakes associated with the Cascadia subduction zone and shallow earthquakes associated with crustal faults across the region.Syracuse Geologist Reveals Correlation Between Earthquakes, Landslides
A geologist in Syracuse University's College of Arts and Sciences has demonstrated that earthquakes--not climate change, as previously thought--affect the rate of landslides in Peru.Magma pancakes beneath Lake Toba
The tremendous amounts of lava that are emitted during super-eruptions accumulate over millions of years prior to the event in the Earth's crust.Rising above the risk: America's first tsunami refuge
Washington's coast is so close to the seismically active Cascadia Subduction Zone that if a megathrust earthquake were to occur, a tsunami would hit the Washington shoreline in just 25 minutes.Journey to the Center of the Earth
A UC Santa Barbara geochemist studying Samoan volcanoes has found evidence of the planet's early formation still trapped inside the Earth. Known as hotspots, volcanic island chains such as Samoa can ancient primordial signatures from the early solar system that have somehow survived billions of years.New study reconstructs mega-earthquakes timeline in Indian Ocean
A new study on the frequency of past giant earthquakes in the Indian Ocean region shows that Sri Lanka, and much of the Indian Ocean, is affected by large tsunamis at highly variable intervals, from a few hundred to more than one thousand years.Mantle plumes crack continents
In some parts of the Earth, material rises upwards like a column from the boundary layer of the Earth's core and the lower mantel to just below the Earth's crust hundreds of kilometres above. Study of Chilean quake shows potential for future earthquake
Near real-time analysis of the April 1 earthquake in Iquique, Chile, showed that the 8.2 event occurred in a gap on the fault unruptured since 1877 and that the April event was not what the scientists had expected, according to an international team of geologists. Studies show movements of continents speeding up after slow 'middle age'
Two studies show that the movement rate of plates carrying the Earth's crust may not be constant over time.
More Subduction Current Events and Subduction News Articles
by Todd Shimoda (Author), L.J.C. Shimoda (Illustrator)
"Shimoda is a consummate storyteller" Booklist
"Shimoda skillfully weaves (these) tales into the narrative, revealing how past events "continue to affect the island, like aftershocks." Earthquakes are an apt metaphor for the social disruptions on the island, and Shimoda links modern earthquake science, ancient Japanese myths on the origin of earthquakes, and an unforgettable cast of characters to create a suspenseful, richly illustrated novel." Publishers Weekly
"Husband and wife team Todd and Linda Shimoda’s skills blend seamlessly together to make Subduction a hauntingly beautiful and highly unique novel. The author’s prose and illustrator’s talent give the book a tone and quality that is both rare and memorable." ForeWord
"Subduction heaves with a...
Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco (Special Publications)|
by Clyde Wahrhaftig (Author)
Published by the American Geophysical Union as part of the Special Publications Series.It is hard to be unaware of the earth in San Francisco. Built on rocky hills, the city is surrounded on three sides by bay and ocean that can be seen from nearly everywhere within it. Precipitous cliffs face the city from across the Golden Gate, and the skyline to the north, east, and south is dominated by mountains. Occasional tremors from the San Andreas and related faults nearby remind us that the earth here is active. Until recently the rocks so abundantly exposed in San Francisco baffled geologists. Jumbled together without apparent order and lacking visible fossils, they defied explanation. The theory of plate tectonics has changed all that. We now have an explanation for the origin of the rocks...
Inside the Subduction Factory (Geophysical Monograph Series)|
by John Eiler (Editor)
Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 138.
Subduction zones helped nucleate and grow the continents, they fertilize and lubricate the earth's interior, they are the site of most subaerial volcanism and many major earthquakes, and they yield a large fraction of the earth's precious metals. They are obvious targets for study—almost anything you learn is likely to impact important problems—yet arriving at a general understanding is notoriously difficult: Each subduction zone is distinct, differing in some important aspect from other subduction zones; fundamental aspects of their mechanics and igneous processes differ from those in other, relatively well-understood parts of the earth; and there are few direct samples of...
Subduction Zone Geodynamics (Frontiers in Earth Sciences)|
by Serge Lallemand (Editor), Francesca Funiciello (Editor)
Subduction is a major process that plays a first-order role in the dynamics of the Earth. The sinking of cold lithosphere into the mantle is thought by many authors to be the most important source of energy for plates driving forces. It also deeply modifies the thermal and chemical structure of the mantle, producing arc volcanism and is responsible for the release of most of the seismic energy on Earth. There has been considerable achievements done during the past decades regarding the complex interactions between the various processes acting in subduction zones. This volume contains a collection of contributions that were presented in June 2007 in Montpellier (France) during a conference that gave a state of the art panorama and discussed the perspectives about "Subduction...
by Colin Setterfield
The Pacific Northwest region of the North American continent is a prolific seismic area. The Cascadia Subduction Zone stretches from Vancouver Island down to Cape Mendocino, California, separating the Juan de Fuca and North American plates. It holds a great potential for spawning the ‘Big One’, a megathrust earthquake that could have devastating consequences for the region.
Paul Brinkworth, a seismologist with the Geoscience Center in Victoria, a city of Vancouver Island and capital of British Columbia, has a dilemma. Due to recent seismic tremors, emanating from the neighboring subduction zone, he is convinced that a megathrust quake is about to take place. Does he go public with a theory and risk his career or does he remain silent, allowing nature to take its course? The...
Collision and Collapse at the Africa-Arabia-Eurasia Subduction Zone - Special Publication no 311 (Geological Society Special Publication)|
by D. J. J. Van Hinsbergen (Author), M. A. Edwards (Author), R. Govers (Author), D. J. J. Van Hinsbergen (Editor), M. A. Edwards (Editor), R. Govers (Editor)
The Mediterranean and northern Arabian regions provide a unique natural laboratory to constrain geodynamics associated with arc-continent and continent-continent collision and subsequent orogenic collapse by analysing regional and temporal distributions of the various elements in the geological archive. This book combines thirteen new contributions that highlight timing and distribution of the Cretaceous to Recent evolution of the Calabrian, Carpathian, Aegean and Anatolian segments of the Africa-Arabia-Eurasia subduction zone. These are subdivided into five papers documenting the timing and kinematics of Cretaceous arc-continent collision, and Eocene and Miocene continent-continent collision in Anatolia, with westward extrusion of Anatolia as a result. Eight papers provide an overview...
Subduction Top to Bottom (Geophysical Monograph Series)|
by Gray E. Bebout (Editor), David W. Scholl (Editor), Stephen H. Kirby (Editor), John P. Platt (Editor)
Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 96.
Perhaps no other plate tectonic setting has attracted as diverse multidisciplinary attention as convergent margins. This has in part been spurred by the extremely tangible hazards imposed by subduction, particularly in the form of earthquakes and tsunamis and arc volcanism. Concern regarding these hazards is heightened by the tendency of convergent margins to be heavily populated coastal regions. There has also been great interest in convergent margin settings for their potential (and demonstrated capability) of producing economically important oil and gas reservoirs and ore deposits. The cycling of materials (e.g., CO2 at convergent margins has been recognized as potentially...
Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes (Geological Society Special Publication)|
by R. D. Larter (Author)
Recycling of oceanic plate back into the Earth's interior at subduction zones is one of the key processes in Earth evolution. Volcanic arcs, which form above subduction zones, are the most visible manifestations of plate tectonics, the convection mechanism by which the Earth loses excess heat. They are probably also the main location where new continental crust is formed, the so-called 'subduction factory'. About 40% of modern subduction zones on Earth are intra-oceanic. These subduction systems are generally simpler than those at continental margins as they commonly have a shorter history of subduction and their magmas are not contaminated by ancient sialic crust. They are therefore the optimum locations for studies of mantle processes and magmatic addition to the crust in subduction...
The Cascadia Subduction Zone and Related Subduction Systems: Seismic Structure, Intraslab Earthquakes and Processes, and Earthquake Hazards: Open-File Report 2002-328|
by Stephen H. Kirby (Author), United U.S. Department of the Interior (Creator), et al. (Creator)
The United States Geological Survey (USGS) is a scientific organization created in 1879, and is part of the U.S. government. Their scientists explore our environment and ecosystems, to determine the natural dangers we are facing. The agency has over 10,000 employees that collect, monitor, and analyze data so that they have a better understanding of our problems. The USGS is dedicated to provide reliable, investigated information to enhance and protect our quality of life. This is one of their circulars.
The Seismogenic Zone of Subduction Thrust Faults (MARGINS Theoretical and Experimental Earth Science Series)|
by Timothy H Dixon (Editor), Casey Moore (Editor)
Subduction zones, one of the three types of plate boundaries, return Earth's surface to its deep interior. Because subduction zones are gently inclined at shallow depths and depress Earth's temperature gradient, they have the largest seismogenic area of any plate boundary. Consequently, subduction zones generate Earth's largest earthquakes and most destructive tsunamis. As tragically demonstrated by the Sumatra earthquake and tsunami of December 2004, these events often impact densely populated coastal areas and cause large numbers of fatalities. While scientists have a general understanding of the seismogenic zone, many critical details remain obscure. This volume attempts to answer such fundamental concerns as why some interplate subduction earthquakes are relatively modest in rupture...