Final answer:
The activity not commonly associated with continent-continent collisions is volcanism. These types of collisions lead to mountain building, but not to significant volcanic activity, as no plate is subducted to create magma.
Step-by-step explanation:
Continent-continent collisions, known as orogeny, are processes that form mountains through intense geological activities. The correct answer to the activity not commonly associated with continent-continent collisions is volcanism (option b). This contrasts with other listed activities such as plutonism (a), thrust faulting (c), regional metamorphism (d), and mountain building (e), which are typically involved. Volcanism is more commonly associated with oceanic-continental subduction zones rather than collisions between continental plates.
During continent-continent collisions, the two continental plates are of similar density and buoyancy, which prevents one from being subducted beneath the other. Instead, the crust is typically pushed upwards or thrust sideways, leading to mountain ranges, such as the Himalayas or the Alps, without the formation of a significant number of volcanic structures. Volcanism is more common in subduction zones where an oceanic plate, being denser, slides beneath a continental plate or another oceanic plate, leading to magma formation and volcanic activity.