Question

Which of the following rocks occurs typically in a ductile shear zone?

• A. Gouge
• B. Breccia
• C. Pseudotachylite
• D. Mylonite

Hint:

Mylonites are characteristic of ductile shear zones, formed under conditions of high strain and low to moderate temperatures.

Answer 1

The Correct Option is D

Step 1: Understanding Ductile Shear Zones.
Ductile shear zones are zones of deformation where rocks are subjected to high strain, leading to the formation of fine-grained, deformed rocks. These rocks typically exhibit a foliated texture.
Step 2: Analyzing the options.
(A) Gouge: Incorrect — Gouge is a fine-grained material formed by the grinding and breaking of rock along faults, but it is not typical of ductile shear zones.
(B) Breccia: Incorrect — Breccia consists of angular fragments and is associated with brittle deformation, not ductile shear zones.
(C) Pseudotachylite: Incorrect — Pseudotachylite forms in frictionally heated rocks during faulting, but it is not typical of ductile shear zones.
(D) Mylonite: Correct — Mylonite forms in ductile shear zones due to intense deformation and fine-grained texture.
Step 3: Conclusion.
The correct answer is (D) Mylonite, as it is the rock typically found in ductile shear zones.