Question

Coarse grain size in metamorphic rocks typically means that the rock?

1) experienced metamorphism for only a very short period of time
2) experienced low pressure
3) experienced low temperature
4) experienced relatively high pressure and temperature for a long period of time
5) protolith must also have been coarse grained

Answer 1

Coarse grain size in metamorphic rocks means that the rock has experienced high temperature and pressure for a sustained period, indicating a significant recrystallization process.

Step-by-step explanation:

Coarse grain size in metamorphic rocks typically indicates that the rock has experienced relatively high pressure and temperature for a long time during its formation. The metamorphism process includes the alteration of a pre-existing rock known as the protolith, through recrystallization of its mineral content under high-temperature and high-pressure conditions. Grain size in metamorphic rocks is a function of the conditions the rock was subjected to during metamorphism. Larger grains form under higher temperatures and pressures and usually require a longer period of time to grow. This suggests that a coarse-grained metamorphic rock has undergone significant recrystallization, pointing to option 4) experienced relatively high pressure and temperature for a long period of time.