Question

The progressive metamorphic isograd sequence that explains Barrovian metamorphism in pelite is

• A. chlorite $\rightarrow$ staurolite $\rightarrow$ biotite $\rightarrow$ kyanite $\rightarrow$ sillimanite
• B. chlorite $\rightarrow$ andalusite $\rightarrow$ cordierite $\rightarrow$ sillimanite
• C. chlorite $\rightarrow$ biotite $\rightarrow$ garnet $\rightarrow$ staurolite $\rightarrow$ kyanite $\rightarrow$ sillimanite
• D. sillimanite $\rightarrow$ kyanite $\rightarrow$ staurolite $\rightarrow$ garnet $\rightarrow$ biotite $\rightarrow$ chlorite

Hint:

In Barrovian metamorphism, the progressive appearance of minerals such as chlorite, biotite, garnet, staurolite, kyanite, and sillimanite indicates increasing pressure and temperature.

Answer 1

The Correct Option is C

Step 1: Understanding the question.
The question asks about the sequence of isograds (lines of equal metamorphic grade) that describes the Barrovian metamorphism in pelite (fine-grained sedimentary rock).
Step 2: Analyzing the options.
(A) chlorite $\rightarrow$ staurolite $\rightarrow$ biotite $\rightarrow$ kyanite $\rightarrow$ sillimanite: This sequence is incorrect because the correct sequence includes garnet before staurolite.
(B) chlorite $\rightarrow$ andalusite $\rightarrow$ cordierite $\rightarrow$ sillimanite: This is a different type of metamorphism and not the Barrovian sequence.
(C) chlorite $\rightarrow$ biotite $\rightarrow$ garnet $\rightarrow$ staurolite $\rightarrow$ kyanite $\rightarrow$ sillimanite: Correct — This is the typical Barrovian sequence for pelite, progressing from low-grade metamorphic minerals to high-grade minerals.
(D) sillimanite $\rightarrow$ kyanite $\rightarrow$ staurolite $\rightarrow$ garnet $\rightarrow$ biotite $\rightarrow$ chlorite: This sequence is the reverse of the correct one.
Step 3: Conclusion.
The correct answer is (C) chlorite $\rightarrow$ biotite $\rightarrow$ garnet $\rightarrow$ staurolite $\rightarrow$ kyanite $\rightarrow$ sillimanite, as it is the correct Barrovian sequence for pelite.