Question

The assemblage staurolite + garnet + biotite + muscovite + quartz in pelites is stable in

• A. greenschist facies
• B. amphibolite facies
• C. granulite facies
• D. pyroxene hornfels facies

Hint:

In metamorphic rocks, different mineral assemblages are stable at different temperatures and pressures, with the amphibolite facies being associated with medium to high-grade conditions.

Answer 1

The Correct Option is B

Step 1: Understanding facies and mineral assemblages.
Facies are used to describe the metamorphic conditions (temperature and pressure) under which specific mineral assemblages form. The given assemblage of staurolite, garnet, biotite, muscovite, and quartz typically forms in the amphibolite facies, which corresponds to medium to high-grade metamorphism.

Step 2: Analyzing the options.
(A) greenschist facies: Greenschist facies is a lower-grade metamorphic condition and does not stabilize the mentioned assemblage.
(B) amphibolite facies: This is the correct answer. The given mineral assemblage is typical for the amphibolite facies.
(C) granulite facies: Granulite facies represents high-grade metamorphism, which would typically involve different mineral assemblages.
(D) pyroxene hornfels facies: This is incorrect, as hornfels facies involves minerals like pyroxenes and feldspars, not the mentioned assemblage.

Step 3: Conclusion.
The correct answer is (B) amphibolite facies.