Question

Which of the following rocks is/are characteristic of fossil subduction zones?

• A. Wollastonite and scapolite bearing skarn
• B. Andalusite and staurolite bearing hornfels
• C. Garnet and glaucophane bearing blueschist
• D. Garnet and omphacite bearing eclogite

Hint:

Blueschist and eclogite are key metamorphic rocks that form in subduction zones, representing high-pressure, low-temperature conditions.

Answer 1

The Correct Option is C, D

Step 1: Understanding subduction zones
Subduction zones are areas where one tectonic plate is forced beneath another. These zones are marked by high pressure and low temperature, which lead to the formation of specific types of metamorphic rocks. The minerals formed in these conditions provide important indicators of subduction-related processes.

Step 2: Rock Types and Their Association with Subduction Zones
Let's evaluate each option:

❌ Option (A) Wollastonite and scapolite bearing skarn:
Skarn forms due to contact metamorphism, which occurs when magma interacts with limestone or dolomite. This is not associated with subduction zones. Wollastonite and scapolite can form in these conditions, but they are not typical of subduction zones.

❌ Option (B) Andalusite and staurolite bearing hornfels:
Hornfels forms under conditions of contact metamorphism due to heating by an intruding magma body. It is not associated with subduction zones. Andalusite and staurolite are also high-temperature minerals, and they form under lower-pressure conditions, not typically in subduction zones.

✅ Option (C) Garnet and glaucophane bearing blueschist:
Blueschist is a rock that forms in high-pressure, low-temperature conditions, characteristic of subduction zones. The presence of garnet and glaucophane in blueschist is a classic indicator of subduction zone metamorphism.

✅ Option (D) Garnet and omphacite bearing eclogite:
Eclogite is another high-pressure rock that forms deeper than blueschist, also characteristic of subduction zones. Garnet and omphacite are common minerals found in eclogite, indicating its formation at great depths in subduction zones.

Step 3: Conclusion
The correct answers are Option (C) and Option (D), as both blueschist and eclogite are characteristic of subduction zones, with garnet and glaucophane found in blueschist and garnet and omphacite found in eclogite.