- published: 07 Jun 2011
- views: 112567
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge. Regions where this process occurs are known as subduction zones. Rates of subduction are typically centimetres per year, with the average rate of convergence being approximately two to eight centimetres per year.
Plates include both oceanic crust and continental crust. Stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental lithosphere or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the subducted lithosphere is always oceanic while the over-riding lithosphere may or may not be oceanic. Subduction zones are sites that have a high rate of volcanism, earthquakes, and mountain building.
Orogenesis, or mountain-building, occurs when large pieces of material on the subducting plate (such as island arcs) are pressed into the over-riding plate or when subhorizontal contraction occurs in the over-riding plate. These areas are subject to many earthquakes, which are caused by the interactions between the subducting slab and the mantle, the volcanoes, and (when applicable) the mountain-building related to island arc collisions.
In this video an introduction to seafloor spreading, subduction and megathrust earthquakes are animated to allow for easier understanding of the topics. The Cascadia Subduction Zone is used as the example. An area where the Juan de Fuca plate is being subducted under the North American Plate. We use images that can be found on our World Satellite Map. and please comment if you like the video and its useful ;-) For an up-to-date map of the Earth's tectonic plates goto: http://www.science-story.com/satellite-world-map-up-to-date-large-poster.php For more videos and information goto www.science-story.com
This replaces previous subduction animation. www.iris.edu/educate In this animation, we are showing an ocean/continent convergent boundary. We see the denser thinner oceanic plate diving beneath the continental plate. The down-going oceanic plate eventually melts and gets absorbed into the mantle. Such destruction (recycling) of crust takes place along convergent boundaries where plates collide and a 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.) More info at: http://www.iris.edu/hq/programs/education_and_outreach/aotm/11 Uploader Comments ( IRISEnO ) This animation doesn't show magma formation, which would be at depth off th...
We find that oceanic crust subducted to the lowermost mantle is viscously dragged toward upwelling regions, where primordial reservoirs are hypothesized to exist. While most oceanic crust avoids interaction with a reservoir itself and is entrained into thermal plumes that form along the tops of reservoirs, some crust accumulates at the base of the plumes, along reservoir tops. Eventually the volume of accumulated crust at the base of a plume gains enough negative buoyancy such that it is flushed into the reservoir below, through the reservoir's top margin. These three panels are temperature, viscosity and composition (blue for primordial reservoir and yellow for oceanic crust).
For more, visit http://science.discovery.com | Just outside New Zealand, White Island sits at the junction of the Pacific and Australian tectonic plates. At this point, the floor of the Pacific Ocean dives down deep below the Australian plate.
The results of our numerical melding shows that, under present-day Earth-like conditions, it is difficult for the subducted oceanic crust to accumulate into large thermochemical piles at the core-mantle boundary. The three panels are temperature, viscosity and composition respectively. We see that the major parts of the subducted oceanic crust are carried up by upwelling plumes and mixed with ambient mantle, instead of settle at the core-mantle boundary.
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