Answer :
Final answer:
Temperatures associated with metamorphism typically range from 400°C to 1000°C. Among the options, 400°C relates to the formation of low-grade metamorphic index minerals, and 900°C to high-grade metamorphic minerals.
Explanation:
The temperature range associated with metamorphism is quite broad, typically varying from 400°C to 1000°C. Metamorphic processes occur under subsolidus conditions, which means that the temperatures are high enough for recrystallization of rocks without melting them. Among the given options, 900°C and 400°C are temperatures within this range. Specifically, 400°C is commonly associated with the formation of certain index minerals such as chlorite in low-grade metamorphic rocks, while higher temperatures, such as 900°C, are associated with high-grade metamorphic rocks, which can contain minerals like sillimanite before the rocks begin to melt into migmatites.
