Divergent and Convergent Plate Boundaries
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Spreading mid-ocean ridges form the longest mountain ranges in the world. New oceanic crust is created at this boundary when basalt magma, formed in the mantle, rises into fractures in the crust and solidifies. Spreading ridges are high elevation because the young oceanic plate at the ridge crest is hot and less dense than the older, colder and more dense plate on the flanks of the ridge. As the plates move away from the boundary, they thicken because underlying mantle rocks cool and add to the bottom of the plate.
In this animation, we are showing an ocean/continent convergent boundary. We see the denser oceanic plate diving beneath the continental plate. The down-going oceanic plate eventually warms up to the temperature of the surrounding mantle. Such destruction (recycling) of oceanic plates occurs along convergent boundaries where plates collide and an oceanic plate is subducted. (This animation does not address volcanoes formed inboard of the boundary where water released from the oceanic plate facilities magma production in the mantle wedge beneath the continent.)
Simple example of a strike slip fault. Additional examples of processes associated with strike-slip faults is on the Animation of Month: Asperities (For other fault animations go to Earthquake Faults.) The 38-million-year history of the San Andreas Fault of California was animated by Tanya Atwater, U.C. Santa Barbara and can be downloaded.
Video lecture by Dr. Robert Butler on the four basic types of plate tec- tonic boundaries. This was recorded at a workshop for middle-school Earth- science teachers in 2006. Other short video lectures by Dr. But- ler can be downloaded from his TOTLE page.
Animations and videos are made in partnership with Earthscope, USGS, and Volcano Video & Graphics.
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