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 ArticlesStudy 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. New evidence for oceans of water deep in the Earth
Researchers from Northwestern University and the University of New Mexico report evidence for potentially oceans worth of water deep beneath the United States.Ancient rocks yield clues about Earth's earliest crust
It looks like just another rock, but what Jesse Reimink holds in his hands is a four-billion-year-old chunk of an ancient protocontinent that holds clues about how the Earth's first continents formed.Deep earth recycling of the oceanic floor
Scientists from the Magma and Volcanoes Laboratory (CNRS/IRD/Université Blaise Pascal) and the European Synchrotron, the ESRF, have recreated the extreme conditions 600 to 2900 km below the Earth's surface to investigate the melting of basalt in the oceanic tectonic plates.Great earthquakes, water under pressure, high risk
The largest earthquakes occur where oceanic plates move beneath continents. Obviously, water trapped in the boundary between both plates has a dominant influence on the earthquake rupture process.Computer models solve geologic riddle millions of years in the making
An international team of scientists that included USC's Meghan Miller used computer modeling to reveal, for the first time, how giant swirls form during the collision of tectonic plates - with subduction zones stuttering and recovering after continental fragments slam into them.Is there an ocean beneath our feet?
Scientists at the University of Liverpool have shown that deep sea fault zones could transport much larger amounts of water from the Earth's oceans to the upper mantle than previously thought.Vancouver: Nearby Georgia basin may amplify ground shaking from next quake
Tall buildings, bridges and other long-period structures in Greater Vancouver may experience greater shaking from large (M 6.8 +) earthquakes than previously thought due to the amplification of surface waves passing through the Georgia basin.Global map to predict giant earthquakes
A team of international researchers, led by Monash University's Associate Professor Wouter Schellart, have developed a new global map of subduction zones, illustrating which ones are predicted to be capable of generating giant earthquakes and which ones are not.
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...
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...
Subduction: Insights from Physical Modeling (Modern Approaches in Geophysics)|
by Alexander I. Shemenda (Author)
This book is devoted to the quantitative physical modeling of subduction and subduction-related processes. It presents a coherent description of the modeling method (including similarity criteria, and a novel applied experimental technique), results from model experiments, theoretical analysis of results on the basis of continuum mechanics, and their geodynamic interpretation. Subduction is modeled in general as well as applied to particular regions using both 2-D and 3-D approaches, with both slab-push and slab-pull driving forces. The modeling covers all stages from subduction initiation to `death', different regimes of subduction producing back arc extension and compression, blocking of subduction and jumps of subduction zone, arc-continent collision and continental...
by Emily Mcgiffin (Author)
Subduction Zone is a book of meditations on empire — the desires and agendas of empire, and empire’s detritus. From a sweeping panorama of imperial landscapes both classical and modern, it carries us into the troubled natural beauty of the world. Its third and final sequence brings Canadians home, to the manifestations of global technocracy in northwest BC.Whether contemplating rain forests in the Visayan Islands or Edward Burtynsky’s photographs, these poems gaze unflinchingly at the exploitation and upheaval that define several millennia of global politics. Their questions are both urgent and intricate. Who are we individually, collectively, in this era of looming ecological collapse? How do we acknowledge the blood on our hands yet bear witness to the beauty that remains?...
Subduction Zone Magmatism (Frontiers in Earth Sciences)|
by Yoshiyuki Tatsumi (Author), Steve Eggins (Author)
Subduction zones are major sites of volcanism on the Earth. As one crustal plate sinks or is pushed beneath another, hot magma is produced and the resultant magma flux is fundamental to both the thermal evolution and chemical differentiation of the mantle and the Earth itself. To understand these evolutionary processes, we need to understand the physical and chemical consequences of all aspects of the subduction process. In this book, the authors present a simple, current and comprehensive model that explains the dominant geological processes at work in subduction zones. Structuring the book around the model, the authors describe the physical characteristics and geochemical dynamics of subduction zones, arc magma generation, and the dynamics and flow in the mantle. Students and...
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...
by Christopher Scholz (Author)
Deep beneath the Pacific Northwest lies the Cascadia subduction zone—an earthquake factory that is long overdue for a “big one.” Tensions have been building for over three centuries, and it’s not a matter of if but when and how big. Retired earthquake expert Carl Strega thinks he may know, and it’s much sooner than anyone would like to think. But he can’t rush his discovery to the scientific community or the media just yet because his data is based on a cutting edge, unproven branch of chaos theory. Avoiding the destruction of his reputation and mass hysteria is the order of the day. Carl secretly assembles a team of local university researchers to put his theory to the test, but they only have so much time. Before they’re finished, word gets out that a magnitude-nine...
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...
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...