When two continental plates collide, neither is easily subducted due to their relatively low density compared to the mantle. Instead, the crustal material is compressed and forced upward, resulting in the formation of fold mountains. This process of folding is a fundamental mechanism in mountain building, as seen in the formation of the Himalayas through the collision of the Indian and Eurasian plates.

Continental crust is significantly thicker than oceanic crust. Continental crust typically ranges from 30 to 50 kilometers in thickness, composed primarily of granitic rocks, whereas oceanic crust is much thinner, usually averaging about 5 to 10 kilometers, and is composed primarily of denser basaltic rocks.

A destructive plate boundary, also known as a convergent boundary, occurs where two tectonic plates move toward each other. In cases involving oceanic crust, the denser plate is forced beneath the other into the mantle, where it is recycled and destroyed, a process known as subduction.

Convergent plate boundaries occur where two tectonic plates move toward one another. This interaction often results in subduction, where one plate is forced beneath the other, or the formation of mountain ranges through crustal thickening. These zones are characterized by intense seismic activity, volcanic eruptions, and significant geological deformation over geological timescales.

The Mid-Atlantic Ridge is the most prominent example of a divergent plate boundary where seafloor spreading occurs. As the North American and Eurasian plates move apart, magma rises from the mantle to form new oceanic crust. While other oceans have spreading centers, the Atlantic is characterized by a continuous, well-defined ridge system running through its center.

Continental crust is primarily composed of granitic rocks, which are less dense than the basaltic rocks that make up the oceanic crust. Because continental crust is less dense, it 'floats' higher on the mantle, making it effectively lighter in terms of buoyancy compared to the denser, thinner oceanic plates that sink during subduction processes.

When tectonic plates move apart at divergent boundaries, the pressure on the underlying mantle is reduced, causing partial melting. This results in the formation of magma, which rises to fill the gap. Upon reaching the surface or cooling beneath it, this magma solidifies to form new crust, effectively sealing the rift created by the diverging plates.

Subduction occurs at convergent plate boundaries where a denser oceanic plate sinks into the mantle beneath a less dense continental or oceanic plate. This process is a primary driver of volcanic activity, deep-sea trench formation, and seismic events, playing a crucial role in the Earth's tectonic cycle.

A transform plate boundary, often referred to in some contexts as a conservative or passive boundary, occurs where plates slide past each other. Unlike constructive (divergent) or destructive (convergent) boundaries, crust is neither created nor destroyed here. The friction between these plates often leads to significant seismic activity, such as the San Andreas Fault, as stress builds up and is released as earthquakes.

The collision between the South American Plate and the Nazca Plate is a textbook example of oceanic-continental subduction. The denser Nazca Plate is forced beneath the lighter South American Plate, leading to the formation of the Andes Mountains and significant volcanic and seismic activity along the western coast of South America.