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13

As you said, the Andean belt is divided into four segments, usually called the northern, central, southern, and austral volcanic zones (NVZ, CVZ, SVZ and AVZ, respectively; your map lacks the AVZ). This has been interpreted as a difference in the angle of subduction. Under the active zones, the subducting plate (called "slab") sinks into the mantle, ...


5

So, this is the setting. A relatively young plate plate is subducted under the south American continent. The subducting oceanic plate contains water that is squeezed out under pressure and starts to rise. Water (fluids) generally lower the melting point, so hot asthenosphere above the colder subducting plate partially melts, the magma, being more mobile, ...


-1

When an oceanic plate is subducted below a continental plate, it dives into the mantle, taking water with it and producing frictional heat which melts some of the rock (rock with a high water content melts more easily). This produces plumes of magma beneath the continental plate margins. As the magma is lighter than the mantle material, it rises until it ...


4

It is continental crust which hs the greater buoyancy, so when it meets another plate of continental crust neither can subduct. Instead, they collide, crumple and fold, making them thicker and higher. An example of this is the collision between the Indo-Australian plate and the Eurasian plate, which has formed the Himalayas. Had the Indo-Australian plate ...


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