Question

The metamorphic facies series that explains oceanic subduction zone metamorphism is

• A. Prehnite-Pumpellyite → Blueschist → Eclogite
• B. Greenschist → Epidote amphibolite → Amphibolite → Granulite
• C. Albite-epidote hornfels → Hornblende hornfels → Pyroxene hornfels → Sanidinite
• D. Greenschist → Amphibolite → Granulite → Eclogite

Hint:

In oceanic subduction zones, the typical metamorphic facies series progresses from Prehnite-Pumpellyite to Blueschist to Eclogite.

Answer 1

The Correct Option is A

Step 1: Understanding metamorphic facies series.
The Prehnite-Pumpellyite to Blueschist to Eclogite facies series represents the progressive metamorphism of rocks in oceanic subduction zones, where the pressure and temperature increase with depth.

Step 2: Analyzing the options.
(A) Prehnite-Pumpellyite → Blueschist → Eclogite: Correct — This is the typical sequence of metamorphism in an oceanic subduction zone, where blueschist forms at high pressure but relatively low temperature, and eclogite forms at higher pressures.
(B) Greenschist → Epidote amphibolite → Amphibolite → Granulite: This sequence is more characteristic of regional metamorphism at moderate pressures and temperatures.
(C) Albite-epidote hornfels → Hornblende hornfels → Pyroxene hornfels → Sanidinite: This sequence relates to contact metamorphism, not subduction zones.
(D) Greenschist → Amphibolite → Granulite → Eclogite: Incorrect, as this does not follow the typical sequence for oceanic subduction zones.

Step 3: Conclusion.
The correct answer is (A) Prehnite-Pumpellyite → Blueschist → Eclogite.