Metamorphism occurs predominantly in which deformation zone?

• A. Ductile zone
• B. Brittle zone
• C. Surface zone
• D. Asthenospheric zone

Answer: (A)

Metamorphism happens when rocks are subjected to enough heat and pressure that minerals recrystallize and textures realign as the rock deforms. This process occurs best where rocks flow plastically rather than crack, which is the ductile zone. In the ductile zone, temperatures and pressures are high enough with depth to drive mineral changes and the development of metamorphic textures like foliation. Near the surface, rocks stay cool and tend to fracture (brittle behavior) rather than metamorphose, and the surface zone isn’t conducive to metamorphism. The asthenospheric zone is mantle and can deform in a ductile manner, but the typical focus for metamorphism in introductory geology is crustal rocks undergoing ductile deformation. So, metamorphism occurs predominantly in the ductile zone.