Which plate tectonic setting is most likely to promote the formation of metamorphic rocks?

Which plate tectonic setting is most likely to promote the formation of metamorphic rocks?

• A. Convergent boundary
• B. Divergent boundary
• C. Transform boundary
• D. Intraplate volcanism

Answer: (A)

Metamorphism happens where rocks are exposed to high temperatures and pressures, typically through deep burial, intense compression, or contact with hot intrusions. At convergent boundaries, crust is thickened by collision and one slab is driven down into the mantle (subduction). This creates the elevated pressures and temperatures needed for regional metamorphism, producing a progression of metamorphic rocks such as slate, phyllite, schist, and gneiss as rocks are reorganized under increasing grade. Subduction zones can even generate specific high-pressure facies like blueschist, illustrating how this setting routinely provides the conditions for metamorphism to occur on a large scale. Divergent boundaries mainly involve thinning crust and decompression melting that forms new igneous rocks, not the high P–T conditions that promote widespread metamorphism. Transform boundaries produce significant deformation from shear, which can cause some localized metamorphic textures, but not the extensive high-grade metamorphism typical of collision zones. Intraplate volcanism centers on melting within a plate away from plate boundaries and yields metamorphism only locally near intrusions, not as a dominant process shaping broad metamorphic belts.

Metamorphism happens where rocks are exposed to high temperatures and pressures, typically through deep burial, intense compression, or contact with hot intrusions. At convergent boundaries, crust is thickened by collision and one slab is driven down into the mantle (subduction). This creates the elevated pressures and temperatures needed for regional metamorphism, producing a progression of metamorphic rocks such as slate, phyllite, schist, and gneiss as rocks are reorganized under increasing grade. Subduction zones can even generate specific high-pressure facies like blueschist, illustrating how this setting routinely provides the conditions for metamorphism to occur on a large scale.

Divergent boundaries mainly involve thinning crust and decompression melting that forms new igneous rocks, not the high P–T conditions that promote widespread metamorphism. Transform boundaries produce significant deformation from shear, which can cause some localized metamorphic textures, but not the extensive high-grade metamorphism typical of collision zones. Intraplate volcanism centers on melting within a plate away from plate boundaries and yields metamorphism only locally near intrusions, not as a dominant process shaping broad metamorphic belts.