Breakthrough Achieved in Explaining Why Tectonic Plates Move the Way They Do
ScienceDaily (July 17, 2010) — A team of researchers including Scripps Institution of Oceanography, UC San Diego geophysicist Dave Stegman has developed a new theory to explain the global motions of tectonic plates on the earth's surface.
The sinking of the Farallon plate beneath the North American continent over 30 million years created the geologic feature known as the Basin and Range Province, an area of the western United States that encompasses much of Nevada, seen here in a topographic model. (Credit: Mike Sandiford/University of Melbourne)
The new theory extends the theory of plate tectonics -- a kinematic description of plate motion without reference to the forces behind it -- with a dynamical theory that provides a physical explanation for both the motions of tectonic plates as well as motion of plate boundaries. The new findings have implications for how scientists understand the geological evolution of Earth, and in particular, the tectonic evolution of western North America, in the past 50 million years.
The research, led by Monash University's Wouter Schellart, is published in the July 16 issue of the journal Science.
These findings provide a new explanation as to why tectonic plates move along the Earth's surface at the speeds that are observed, the details of which were previously not well-understood.
"The earth's surface is covered with tectonic plates that move with respect to one another at centimeters per year," Schellart said. "These plates converge at deep-sea trenches, plate boundaries where one plate sinks (subducts) below the other at so-called subduction zones. The velocities of these plates and the velocities of the boundaries between these plates vary significantly on Earth."
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Vol. 329. no. 5989, pp. 316 - 319
DOI: 10.1126/science.1190366
Cenozoic Tectonics of Western North America Controlled by Evolving Width of Farallon Slab
W. P. Schellart,1,* D. R. Stegman,2,3 R. J. Farrington,4 J. Freeman,4,5 L. Moresi1,4
Subduction of oceanic lithosphere occurs through two modes: subducting plate motion and trench migration. Using a global subduction zone data set and three-dimensional numerical subduction models, we show that slab width (W) controls these modes and the partitioning of subduction between them. Subducting plate velocity scales with W2/3, whereas trench velocity scales with 1/W. These findings explain the Cenozoic slowdown of the Farallon plate and the decrease in subduction partitioning by its decreasing slab width. The change from Sevier-Laramide orogenesis to Basin and Range extension in North America is also explained by slabwidth; shortening occurred during wide-slab subduction and overriding-plate–driven trench retreat, whereas extension occurred during intermediate to narrow-slab subduction and slab-driven trench retreat.
1 School of Geosciences, Monash University, Melbourne, Victoria 3800, Australia.
2 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
3 School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia.
4 School of Mathematical Sciences, Monash University, Melbourne, Victoria 3800, Australia.
5 Bureau of Meteorology, Melbourne, Victoria 3001, Australia.
* To whom correspondence should be addressed. E-mail: wouter.schellart@monash.edu
Subduction of oceanic lithosphere occurs through two modes: subducting plate motion and trench migration. Using a global subduction zone data set and three-dimensional numerical subduction models, we show that slab width (W) controls these modes and the partitioning of subduction between them. Subducting plate velocity scales with W2/3, whereas trench velocity scales with 1/W. These findings explain the Cenozoic slowdown of the Farallon plate and the decrease in subduction partitioning by its decreasing slab width. The change from Sevier-Laramide orogenesis to Basin and Range extension in North America is also explained by slabwidth; shortening occurred during wide-slab subduction and overriding-plate–driven trench retreat, whereas extension occurred during intermediate to narrow-slab subduction and slab-driven trench retreat.
1 School of Geosciences, Monash University, Melbourne, Victoria 3800, Australia.
2 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
3 School of Earth Sciences, University of Melbourne, Melbourne, Victoria 3010, Australia.
4 School of Mathematical Sciences, Monash University, Melbourne, Victoria 3800, Australia.
5 Bureau of Meteorology, Melbourne, Victoria 3001, Australia.
* To whom correspondence should be addressed. E-mail: wouter.schellart@monash.edu
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