Question

Which type of material becomes molten rock at subduction zones?

light plates
heavy plates
continental crust
new oceanic crust

Answer 1

Continental crust

Step-by-step explanation:

The main mechanism of formation of the molten rock is by partial fusion of the rocks that form the upper portion of the terrestrial mantle. This fusion of the solid rocks to form the magma is controlled by three physical parameters: (1) its temperature; (2) its pressure; and (3) its composition.

At any given pressure and for any rock composition, an increase in temperature after the solidus point will cause melting. Inside the solid continental crust, the temperature of a rock is controlled by the geothermal gradient and the radioactive decay within the rock. The average values ​​of the geothermal gradient range around 25 ° C / km, with a wide range ranging from a minimum of 5-10 ° C / km in the ocean trenches and in the subduction zones, to a maximum of 30- 80 ° C / km under the ocean ridges and in volcanic arc environments.

The pressure is the other of the factors that determine the fusion, and by this way the formation of the magmas. When the heated material rises by convection which induces flotation and crosses the solidus-liquidus barrier, its temperature is reduced by adiabatic cooling. When this happens, the rock liquefies by melting, turning into molten rock when it reaches the surface. The melt may also result from the reduction of the pressure, in a phenomenon known as decompression fusion.

Answer 2

The correct answer is C.

Subduction zones are convergent ( moving) boundaries between two of the earth's tectonic plates. One of the plates is the oceanic crust. The plates are pieces of crust that slowly move towards each other across the planet's surface. This happens over a period of million years.

When two tectonic plates meet, subduction areas develop. A continental crust converges with an oceanic crust. The oceanic crust is heavier than the continental so it bends and moves downward towards the upper mantle.

The edge of the continental crust gets soaked and begins to melt, moving deeper into the earth. This creates molten rock that accumulates in the magma chamber ( large pool of liquid rock beneath the surface of the earth). The molten rock (magma) is under such great pressure that it can fracture the rock around it and move upward. If it reaches the surface, a volcanic eruption takes place.