PLATE TECTONICS 1


The heavy, oceanic crust of the Nazca Plate pushes under the lighter continental crust – a process called subduction. Where the oceanic crust descends, a deep ocean trench (the Peru–Chile Trench) is formed. Such trenches are the deepest parts of our oceans.


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The oceanic crust begins to melt and is destroyed as it sinks into the earth’s hot mantle. When the crustal material melts it forms batholiths, which are huge underground masses of molten rock or magma. Some of this magma may force its way to the surface to form explosive volcanic mountains.


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Friction between the moving plates causes underground rock to bend and snap. This results in earthquakes.


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The lighter continental crust of the South American Plate is arched and folded (buckled). This causes the great fold mountains of the Andes to form.


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As the heavier plate sinks into the mantle, parts of its upper layers are scraped off by the advancing continental plate. These slabs of scraped crust are called terranes. They pile up against the edge of the fold mountains.


Faultingis another process associated with destructive plate boundaries. Great pressure caused by folding sometimes causes the earth’s crust to split or crack. These splits, such as the one shown in the photograph, are called faults. They are sometimes the routes by which magma makes its way to the earth’s surface. (You will learn more about faulting on page 33.)


Licancabur, a volcanic mountain near the west coast of South America. How did plate tectonics lead to the formation of this mountain?


The results of an earthquake in the Andes. How were tectonic plate movements responsible for this earthquake?


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