The diagram is a cross section showing the Nazca Plate (an oceanic plate) subducting beneath the South American Plate (a continental plate). This region is an example of oceanic-continental convergence. Nazca Plate South American Plate Volcanic arc Oceanic crust Continental crust Lithosphere Asthenosphere Why does oceanic-continental convergence produce a volcanic arc? A. Continental crust is heavier than oceanic crust, so the continental crust sinks, melts, and forms a volcanic arc. B. Oceanic crust is less dense than continental crust, so the two plates slide sideways past each other and form a volcanic arc. OC. Continental crust has the same density as oceanic crust, so the two plates collide, buckle under pressure, and form a volcanic arc. D. Oceanic crust is denser than continental crust, so the oceanic crust sinks and melts, and the magma produced rises up to form a volcanic arc.

In the case of oceanic-continental convergence, the denser oceanic crust of the Nazca Plate is subducting beneath the less dense continental crust of the South American Plate. As the oceanic crust sinks, it is subjected to increasing temperature and pressure, causing it to partially melt. This melting of the subducting oceanic crust generates magma, which then rises to the surface, forming a volcanic arc on the overriding continental plate.

The key reasons why oceanic-continental convergence produces a volcanic arc are:

1. Density difference: Oceanic crust is denser than continental crust, so the oceanic crust sinks beneath the continental crust when the two plates converge.

2. Melting of subducting oceanic crust: As the oceanic crust is subducted, the increase in temperature and pressure causes it to partially melt, generating magma.

3. Magma rise and eruption: The less dense magma rises through the overlying continental crust and erupts at the surface, forming a volcanic arc.

The other options are incorrect:

A. Continental crust is not heavier than oceanic crust, so it does not sink and melt to form a volcanic arc.

B. Oceanic and continental crust do not slide past each other in oceanic-continental convergence; the oceanic crust subducts beneath the continental crust.

C. Continental and oceanic crust do not have the same density, and the collision does not directly cause the formation of a volcanic arc.