CPG Structural Geology & Tectonics Flashcards

In structural geology, a 'boudin' is best described as:

Answer: A sausage-shaped segment of a competent layer pulled apart by extensional strain

Boudins form when a competent (rigid) layer embedded in weaker rock is stretched and pulled apart into discrete segments under extensional stress.

On a stereonet (equal-area or equal-angle projection), a great circle represents:

Answer: A plane in three-dimensional space

A great circle on a stereonet represents the trace of a planar feature (such as a fault, bedding, or foliation plane) projected onto the hemisphere.

In structural geology, 'vergence' refers to:

Answer: The direction toward which folds and thrusts are overturned or transported

Vergence indicates the sense of asymmetry in folds and thrusts, showing the transport direction of the deforming material.

A 'klippe' in structural geology is defined as:

Answer: An erosional remnant of a thrust sheet isolated atop younger rocks

A klippe is an outlier of a nappe or thrust sheet that has been isolated by erosion, leaving older rocks surrounded by younger rocks.

The Sevier fold-and-thrust belt of the western United States formed primarily during which event?

Answer: The Sevier Orogeny (mid-Cretaceous thin-skinned thrusting)

The Sevier Orogeny produced a thin-skinned fold-and-thrust belt from Nevada to Wyoming during the mid-Cretaceous, driven by subduction of the Farallon Plate.

According to Anderson's theory of faulting, which stress condition promotes normal fault development?

Answer: Maximum principal stress (σ1) is vertical; minimum (σ3) is horizontal

Normal faults form when σ1 is vertical (gravitational load) and σ3 is horizontal, causing extensional failure along ~60° dipping fault planes.