Final answer:
The intensity of regional metamorphism can be recognized by indicators such as the index of recrystallization, index minerals, and index polymorphs.
he correct option from the given choices would be 3) index minerals.
Step-by-step explanation:
The intensity of regional metamorphism can be recognized by certain indicators. These indicators include:
Index of recrystallization: This refers to the extent to which minerals within the rock have undergone recrystallization, which is the process of forming new crystals with different shapes and sizes.
Index minerals: These are minerals that are typically associated with specific temperature and pressure conditions. By identifying the presence of specific index minerals, the intensity of metamorphism can be inferred.
Index polymorphs: These are different crystal structures of the same mineral that form under different metamorphic conditions. The presence of specific polymorphs can indicate the intensity of metamorphism.