The Nazca plate is moving eastwards, towards the southern American Plate, at about 79mm every year.

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Where the two plates meet, the denser oceanic lithosphere of the Nazca bowl is compelled down and under the much more buoyant continental lithosphere of the southern American Plate, descending in ~ an angle right into the mantle in a procedure called subduction. This is significant on the s surface by the visibility of the Peru-Chile (or Atacama) Trench.

The friction between the plates stays clear of the subducting oceanic key from slide smoothly. As it descends, it drags versus the overlying plate, bring about both come fracture and also deform. This results in regular shallow focus earthquakes that gain deeperas the s plate descends further, specifying a zone of earthquake foci well-known as a Benioff zone.


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As subduction the the Nazca key continues, some of the sediments that gathered on the s floor (together with few of the s crust) space scraped off and forced (accreted) onto the southern American bowl in a process called “obduction”. This forms an accretionary wedge (or ‘prism’), where layers that the deformed and also metamorphosed sediments and ocean crust are thrust onto the south American Plate along faults – or thrust airplane – adding to the size of the continent.


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Cross ar of an accretionary wedge

Image: Fromwww.searchanddiscovery.com ‘Deepwater Fold-Thrust Belts: no All the Beasts are Equal’, Ana Krueger and Ed Gilbert, 2009

The result of the collision of the 2 plates deforms the top edge that the south American key by urgently the rocks. This crustal shortening rises the vertical thickness whilst to reduce the broad of the lithosphere in the collision ar (imagine a vehicle hitting a hard wall) and also so to produce the fold hills of the Andes.

Continued subduction the the Nazca Plate bring sea water, locked in the s crust, deep right into the mantle. Together the bowl heats up the water is liberated, lowering the melting suggest of the mantle and causing partial melting. This producesmagma, which rises and maybe erupted explosively as andesite at the surface.

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Andesitic magma is less thick than the neighboring material, and also can have a temperature that 1000oC. The is viscous, trapping gases as it rises. The water and gases in andesitic magma account because that the explosive activity of andesitic volcanoes, which typically lie dormant for numerous hundreds or thousands of years. This volcanoes commonly produce ash and pyroclastic flows, too as small amounts that andesitic lava.

Andean volcanoes such as the stratovolcanoLáscar, in north Chile, area an excellent example the this type of activity. Láscar erupted ash and also pyroclastic operation in 1993 and also was still active in 2012.