Question

Which one of the following characteristic mineral assemblages represents eclogite facies metamorphism of a pelitic protolith?

• A. garnet + K-feldspar + sillimanite + cordierite
• B. talc + kyanite + phengite + garnet
• C. chlorite + muscovite + biotite + albite
• D. staurolite + chloritoid + biotite + garnet

Hint:

Eclogite facies metamorphism produces characteristic assemblages like garnet + kyanite + phengite, especially in pelitic protoliths.

Answer 1

The Correct Option is B

Step 1: Understand Eclogite Facies Metamorphism.
Eclogite facies metamorphism typically occurs at high pressure and low temperature conditions. It is known for forming garnet + pyroxene mineral assemblages, but the mineral assemblage of a pelitic protolith will also include other minerals like kyanite and phengite.
Step 2: Analyze the Given Options.
- Option A contains minerals like K-feldspar, sillimanite, and cordierite, which are more characteristic of higher-grade metamorphic facies such as granulite.
- Option B features talc, kyanite, phengite, and garnet, which is typical of eclogite facies.
- Option C features chlorite and muscovite, which are characteristic of lower-grade metamorphism.
- Option D features staurolite and chloritoid, which are associated with the amphibolite facies.
Thus, the correct answer is (B) talc + kyanite + phengite + garnet. Final Answer: \[ \boxed{\text{talc + kyanite + phengite + garnet}} \]