ASBOG Structural Geology and Tectonics 3

Question 1

What does the term 'vergence' describe in fold analysis?

Accepted Answer

The direction toward which a fold or thrust is overturned or displaced

Answer

Vergence indicates the direction of tectonic transport or overturning, typically toward the foreland in fold-and-thrust belts.

Question 2

Which seismic discontinuity separates the mantle from the outer core?

Accepted Answer

Gutenberg discontinuity

Answer

The Gutenberg discontinuity at ~2,900 km depth marks the core-mantle boundary where P-wave velocity drops sharply.

Question 3

Slickensides on a fault surface provide information about what?

Accepted Answer

Direction and sense of slip

Answer

Slickensides are polished striations on fault surfaces that record the direction and often the sense of most recent slip.

Question 4

An ophiolite sequence, from bottom to top, begins with which unit?

Accepted Answer

Ultramafic peridotite

Answer

A complete ophiolite sequence begins with ultramafic peridotite (mantle rock) at the base, overlain by gabbro, sheeted dikes, pillow basalts, and sediments.

Question 5

Isostasy explains which geological observation?

Accepted Answer

Mountain roots extend deep into the mantle to achieve gravitational equilibrium

Answer

Isostasy describes how crustal blocks 'float' on the mantle; mountain belts have deep crustal roots to compensate for their elevated topography.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG Structural Geology and Tectonics 3