ASBOG Structural Geology and Tectonics 5

Question 1

Which structural feature is defined by a 180° change in dip direction over a short horizontal distance?

Accepted Answer

Monocline

Answer

A monocline is a step-like fold where strata dip in one direction, creating a flexure with a change in dip, often draping over a basement fault.

Question 2

The Himalayan mountain belt formed from collision between which two plates?

Accepted Answer

Indian and Eurasian plates

Answer

The Himalayas formed from the collision of the Indian subcontinent with the Eurasian Plate beginning ~50 Ma, creating the highest mountains on Earth.

Question 3

What does a stereonet (equal-area projection) primarily allow a structural geologist to do?

Accepted Answer

Plot and analyze orientations of planes and lines in three dimensions

Answer

Stereonets project 3D orientations of structural features (foliations, faults, fold axes) onto a 2D hemisphere for geometric analysis.

Question 4

In thin-skinned tectonics, deformation is confined to which part of the crust?

Accepted Answer

The sedimentary cover above a basal detachment

Answer

Thin-skinned tectonics involves folding and thrusting only of the sedimentary cover, detached from basement along a décollement horizon.

Question 5

Which type of fold has a horizontal or near-horizontal axial plane with one limb overturned?

Accepted Answer

Recumbent fold

Answer

Recumbent folds have essentially horizontal axial planes, causing one limb to be overturned so beds face downward.

ASBOG - Association of State Boards of Geology Practice Test