Greenschist facies corresponds to which P-T conditions?

• A. High pressure high temperature
• B. Low pressure high temperature
• C. Moderate pressure and low temperature
• D. Very high pressure low temperature

Answer: (C)

Greenschist facies forms during low-grade metamorphism, where temperatures are relatively low to moderate and pressures are not high. At these conditions minerals like chlorite, epidote, albite, and quartz are stable, giving rocks a greenish tint that characterizes this facies. Because the rocks aren’t subjected to extreme heat or deep burial, the P–T range is cool and light to moderate in pressure, distinguishing it from higher-grade facies. In contrast, high pressure with high temperature points to granulite or eclogite facies, very high pressure with low temperature to blueschist, and low pressure with high temperature to near-surface contact metamorphism. So, moderate pressure and low temperature best matches greenschist facies.