Sanidinite facies is characterized by which P-T conditions?

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

Answer: (B)

Metamorphic facies tell us the pressures and temperatures rocks record during metamorphism. Sanidinite facies sit at extremely high temperatures but only modest confining pressure, which happens in shallow crust where magma imports a lot of heat but burial pressure is light—classic conditions for intense heating during contact metamorphism near igneous intrusions. That combination is best described as low pressure with very high temperature.

Other options imply different environments: high pressure with low temperature would be subduction-zone metamorphism; moderate pressure and temperature align with regional metamorphism; very high pressure with high temperature points to deeper, high-P metamorphism.