Which type of metamorphism involves large-area pressure and temperature increases, producing foliation?

• A. Regional metamorphism
• B. Contact metamorphism
• C. Shock metamorphism
• D. Burial metamorphism

Answer: (A)

Foliation in metamorphic rocks forms when minerals align and recrystallize under directed pressure at elevated temperatures. When these conditions extend over large areas due to tectonic processes like continental collision and crust thickening, regional metamorphism occurs. This widespread, high P–T setting weaves foliation across broad landscapes, producing slate, phyllite, schist, and gneiss with characteristic layered textures.

Localized heating from an igneous intrusion drives contact metamorphism, which raises temperature more than pressure and often yields non-foliated rocks like hornfels. Shock metamorphism results from meteor impacts and creates high-pressure effects with unique mineral changes rather than broad, planar foliation. Burial metamorphism involves depth-related pressure and temperature increase as sediments are buried, and while it can produce some foliation, it typically affects smaller regions and lower grades compared with regional metamorphism.