Geology Chapter 10: Rock Deformation

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What primarily determines whether a rock will undergo ductile or brittle deformation?

The age of the rock and its geological history

The temperature and pressure conditions at depth (correct)

The mineral composition and strength of the rock

The time over which forces are applied (correct)

At what depth is ductile deformation more likely to occur?

At any depth depending on the mineral composition

At medium depths with moderate pressure

At great depths where temperature and pressure are higher (correct)

At shallow depths where rocks are cooler

Which type of rocks is favored for brittle behavior?

Igneous rocks such as granite and basalt (correct)

Sedimentary rocks with a high clay content

Metamorphic rocks with strong internal bonds

Nonsilicate rich rocks like shale

What characterizes a monocline?

It features a single limb formed by vertical displacement along a fault. Signup and view all the answers

Which statement is true regarding the application of force on rocks?

Brittle deformation occurs with rapid application of forces. Signup and view all the answers

In terms of geological formations, what distinguishes a dome from a basin?

A dome exhibits circular upwarping, placing the oldest strata inside. Signup and view all the answers

What is the first step in mapping rock structure?

Identifying the rock type at a surface exposure Signup and view all the answers

Which type of fault is defined by movement parallel to the dip of the fault surface?

Dip-slip fault Signup and view all the answers

What is the distinction between a normal fault and a reverse fault?

A normal fault has downward movement of the hanging wall, while a reverse fault has upward movement. Signup and view all the answers

What occurs in subduction zones?

One tectonic plate is forced beneath another plate. Signup and view all the answers

What characterizes a reverse fault?

The hanging wall moves up relative to the footwall. Signup and view all the answers

What geological feature results from two normal faults?

A horst Signup and view all the answers

Which of the following is true regarding normal faults?

The hanging wall moves down relative to the footwall. Signup and view all the answers

Which statement accurately describes a fault scarp?

It represents the line of the fault on the surface. Signup and view all the answers

In which settings can normal faults commonly be found?

At spreading centers Signup and view all the answers

What type of fault involves horizontal movement with no vertical displacement?

Strike-slip fault Signup and view all the answers

Which process leads to the formation of columnar joints in igneous rock?

Cooling and shrinkage of the rock Signup and view all the answers

How do joints enhance the process of chemical weathering?

By providing pathways for water and chemicals Signup and view all the answers

What is a significant consequence of seepage along joints in a dam structure?

Risk of failure and erosion Signup and view all the answers

Which of the following best describes the formation of exfoliation domes?

Occurring due to unloading of overlying rock Signup and view all the answers

What is the relationship between strike and dip in geological formations?

Dip is always perpendicular to the strike. Signup and view all the answers

In a geologic map, the strike reported as N60oE indicates what?

The strike is 60 degrees east of north. Signup and view all the answers

What characterizes an anticline in geological terms?

Older rocks are found on the inside. Signup and view all the answers

Which of the following describes a syncline?

It is characterized by a trough of downfolded layers. Signup and view all the answers

What defines a plunging anticline?

Its hinge line dips into the ground. Signup and view all the answers

What is the primary force responsible for the formation of anticlines and synclines?

Compressional forces Signup and view all the answers

Which part of a folded rock refers to the imaginary surface that divides the fold as symmetrically as possible?

Axial plane Signup and view all the answers

What features differentiate symmetrical anticlines from asymmetrical ones?

Symmetrical anticlines have limbs at the same angle. Signup and view all the answers

What is the main focus of structural geology?

The study of the deformation of rocks Signup and view all the answers

Which type of stress occurs when forces push rock together and reduce its volume?

Compressive stress Signup and view all the answers

What happens to a rock experiencing elastic deformation when the stress is released?

It rebounds to its original shape Signup and view all the answers

Which type of fault is characterized by the rock above the fault plane moving down relative to the rock below?

Normal fault Signup and view all the answers

How does the orientation of folds and faults contribute to economic geology?

It can trap oil and gas deposits. Signup and view all the answers

What type of deformation occurs when a rock bends or flows without breaking?

Ductile deformation Signup and view all the answers

What is the term for the amount of force acting on the rock causing deformation?

Stress Signup and view all the answers

Which of the following describes shear stress?

Forces push toward each other but parallel Signup and view all the answers

Study Notes

Chapter 10: Deformation of Rocks

Rocks deform in response to stress, resulting in folding, flowing, and fracturing.
Folds and faults are geologic structures.
Structural geology studies the deformation of rocks.
Stress is the amount of force acting on a rock (tectonic forces).
Strain is the shape or volume changes caused by stress (deformation).

Types of Differential Stress

Compressional stress: Forces push rocks together, shortening the rock body and reducing its volume.
Tensional stress (extensional stress): Forces pull rocks apart, elongating the rock body.
Shear stress: Forces push rocks toward each other but parallel to one another.

Types of Deformation

Elastic deformation: A temporary change in shape in response to stress. The rock returns to its original shape when the stress is released.
Ductile deformation: The rock bends or flows, changing its shape without breaking. This change is permanent.
Brittle deformation (brittle failure): The rock fractures and breaks into separate pieces. This change is permanent.

Factors Affecting Ductile or Brittle Deformation

Depth: At shallower depths, rocks are cooler and under lower pressure, favoring brittle deformation. Deeper, hotter rocks under high pressure favor ductile deformation.
Rock type: Silicate-rich rocks (e.g., granite, basalt) tend to be brittle, while non-silicate rocks (e.g., shale) are more ductile due to weaker internal bonds.
Time: Quickly applied forces trigger brittle deformation, while slowly applied forces create ductile deformation.

Mapping Rock Structure

Locate outcrops (surface exposures of rocks) to identify rock types.
Measure the strike and dip of folds, faults, and rock layers.
Plot the strike, dip, and rock type data on a geologic map.

Strike

A line produced by the intersection of a horizontal plane on a rock surface.
Determined by the path a ball would take if rolled on the rock surface.
Reported as an angle relative to north.

Dip

The angle of inclination of a rock surface from the horizontal plane.
Perpendicular to the strike, representing the path a ball would roll down a rock face.
Reported as an angle and a direction (e.g., 30° East).

Parts of a Folded Rock

Limb: The two sides of the fold.
Hinge line (axis): A line drawn along the points of maximum curvature of each layer.
Axial plane: An imaginary surface that divides the fold as symmetrically as possible.

Types of Folds

Anticline: Arching of geologic layers with older rocks inside the fold.
Syncline: Trough, downfolded layers with older rocks on the outside of the fold.
Monocline: A fold with only one limb. Produced by vertical displacement along a fault rather than compression.
Dome: Circular upwarping; oldest strata within.
Basin: Circular downwarping; youngest strata within.

Faults

Faults are fractures with appreciable displacement.
Dip-slip faults: Movement parallel to the dip of the fault surface, creating vertical displacement.
- Normal fault: Hanging wall moves down relative to the footwall (extensional forces).
- Reverse fault: Hanging wall moves up relative to the footwall (compressional forces).
Strike-slip fault: Horizontal movement parallel to the strike.

Features of Faulted Terrain

Horst: Uplifted block bounded by two normal faults.
Graben: Down-dropped block bounded by two normal faults.
Fault-block mountains are produced in normally faulted terrain.

Joints

Joints are fractures with no appreciable displacement.
Common examples include columnar joints (cooling igneous rocks) and sheeting joints (unloading overlying rock).
Important because they enhance chemical weathering, influence stream directions,, and can affect construction projects (like dam failures).

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the fundamental concepts of rock deformation in this quiz based on Chapter 10. Understand the types of stresses and deformation processes, including elastic, ductile, and brittle responses to tectonic forces. Test your knowledge on geological structures and the mechanics behind the changes in rocks.