Question

Which of the following structures is/are associated with duplexes in fold-thrust belts?

• A. Roof thrust
• B. Floor thrust
• C. Imbricate fan
• D. Horses

Hint:

A duplex always consists of a \textbf{floor thrust} at the base, a \textbf{roof thrust} at the top, and a series of stacked slices called \textbf{horses}. An \textbf{imbricate fan} looks similar but is not a duplex because it lacks a roof thrust.

Answer 1

The Correct Option is A, B, D

Step 1: Understanding duplex structures.
A duplex is a stack of thrust-bounded slices (called horses) that develop between a lower bounding fault (floor thrust) and an upper bounding fault (roof thrust). Duplexes are typical in fold–thrust belts and play an important role in accommodating shortening and crustal thickening. Step 2: Evaluate each option.
- (A) Roof thrust:
The roof thrust is the upper bounding fault of a duplex system. It forms the top boundary above which the horses are stacked.
$\Rightarrow$ Correct. - (B) Floor thrust:
The floor thrust is the basal fault of the duplex, acting as the bottom boundary from which horses are sliced and stacked.
$\Rightarrow$ Correct. - (C) Imbricate fan:
An imbricate fan is a different structural geometry involving a set of parallel thrusts branching upward from a common decollement. It is not a duplex because it lacks a roof thrust and stacked horses.
$\Rightarrow$ Incorrect. - (D) Horses:
Horses are the thrust-bounded slices of rock enclosed between the floor and roof thrusts in a duplex. They are the key components of a duplex structure.
$\Rightarrow$ Correct. Step 3: Final Answer.
The structures associated with duplexes in fold–thrust belts are: \[ \boxed{\text{(A) Roof thrust, (B) Floor thrust, and (D) Horses}} \]