Amphibolite facies corresponds to which range of pressure and temperature?

• A. Moderate to higher temperatures, moderate to higher pressures
• B. Low temperatures, low pressures
• C. Very high temperatures, high pressures
• D. Moderate temperatures, low pressures

Answer: (A)

Amphibolite facies occur when rocks experience intermediate to relatively high temperatures together with mid-to-high pressures. The mineral assemblage of amphibole (often hornblende) and plagioclase, sometimes with garnet or biotite, forms under these conditions, signaling a P–T range hotter than greenschist but cooler than granulite. On a P–T diagram this facies sits between the lower-grade greenschist and the higher-temperature granulite, reflecting its mid-to-higher thermal and pressure environment. Roughly, you’re looking at temperatures around 500–750°C and pressures of about 2–8 kilobars (0.2–0.8 GPa), though exact numbers vary with composition. So the correct range is moderate to higher temperatures and moderate to higher pressures. Very high temperatures and pressures point toward granulite or eclogite facies, while low temperatures and pressures align with greenschist.