Which of the following mineral assemblages characterizes blueschist facies metamorphism of a mafic rock?
Show Hint
- Glaucophane + lawsonite
- Hornblende + plagioclase ± epidote ± garnet
- Omphacite + garnet
- Phengite + chlorite + garnet
The Correct Option is A
Solution and Explanation
Blueschist facies is a high-pressure, low-temperature metamorphic facies typically associated with subduction zones. It is characterized by minerals like glaucophane and lawsonite, which form under these conditions.
Step 2: Analyzing the options.
(A) Glaucophane + lawsonite: Correct — These minerals are typical of the blueschist facies, which forms under high-pressure, low-temperature conditions in subduction zones.
(B) Hornblende + plagioclase ± epidote ± garnet: Incorrect — These minerals are more commonly associated with amphibolite facies, not blueschist.
(C) Omphacite + garnet: Incorrect — Omphacite and garnet are associated with eclogite facies, not blueschist.
(D) Phengite + chlorite + garnet: Incorrect — These minerals are more typical of greenschist facies.
Step 3: Conclusion.
The correct answer is (A) Glaucophane + lawsonite, as these minerals are characteristic of blueschist facies.
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