CHP 10 Crustal Deformation

Brittle Deformation FALSE

TRUE or FALSE Rocks subjected to heat will be more likely to go through brittle deformation when stressed.

a fold that is tilted down into Earth

What does the term plunging fold mean?

Domes have the oldest layers in the middle, not the youngest.

You are sitting in class when your professor begins talking about a dome with the inner layers dating back to the Tertiary and its outer layers dating back to the Permian. You immediately know this professor is wrong. What is your evidence?

Rocks would be oldest on the edges and youngest in the middle.

Imagine a syncline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Oldest on the inside of the fold, youngest on the outside

Which of the following best describes the age relationship of the layers in an anticline?

Deformation Study of rock deformation in response to tectonic forces

Which of the following is the best description for structural geology?

Brittle Deformation

rocks will shatter due to pressure.

Folds High - High

Folds form in ________ temperature-________ pressure environments.

Elastic Deformation

Part complete A rubber band being stretched in preparation to fire across the room is an example of what kind of deformation?

Ductile Deformation

Unbending a paper clip wire is an example of what kind of deformation?

Synclines and Anticlines

Which two features are typically found associated with each other? Hint 1. These features are the result of compressional stresses folding the rock units.

strike-slip fault

Which type of fault has NO vertical motion of rocks associated with it?

Fault Tranform Fault

Which type of fault was responsible for the devastation associated with the 1906 earthquake in San Francisco?

Deformation

________ refers to the changes in shape or position of a rock body in response to differential stress.

Fault Reverse Fault

A ________ fault is created when the hanging wall moves up relative to the footwall.

Basin

A ________ is a circular fold where the youngest layers are in the middle and the oldest layers are on the outside.

Dome

A map view of a region shows a circular rock pattern with the oldest rocks in the center of the pattern. What structure would create such a pattern on the surface? Hint 1. Broad upwarping of sedimentary strata, followed by surface erosion, can produce a circular rock pattern on the surface.

Fold

A monocline is a type of a(n) ____ Hint 1. What you need to focus on Think about rock structures formed by ductile deformation.

Monocline A large steplike fold in otherwise flat-lying sedimentary rocks

Choose the correct definition of a monocline: Hint 1. Decoding the term "monocline" Recall that mono = one, and kleinen = incline.

See print out page 24

Deformation - Strain: Types and Depth 24 of 34 Deformation refers to the changes in the original shape, size, or volume of a rock. There are three types of deformation. The first, elastic deformation, is when rock deforms but can still rebound to its original shape. Once the elastic limit of the rock is reached, however, the rock will deform, or fail, in one of two ways: brittle deformation or ductile deformation. Brittle deformation is often referred to as brittle failure because the structure of the rock "fails" and breaks under pressure. Brittle deformation often occurs near Earth's surface and results in faults and fractures. Ductile deformation occurs when the rock is able to bend and flow almost like bread dough, creating complex shapes. This form of deformation typically occurs at great depths within Earth's crust. These three types of deformation can be expressed in folds, faults, and joints. Part A - The types of deformation Identify the type of deformation the rock has been exposed to. Drag the appropriate labels to their respective targets. Hint 1. The characteristics of elastic rebound Elastic rebound cannot be observed in real time and is purely a state of pressure. It can be visualized as a rock bending under pressure, and then snapping back to its original state.

Compressional When compressional stress is exerted on rocks at depth, they can be bent (ductile deformation) and folds are formed.

During deformation of sedimentary rocks, which type of stress produces folds? Hint 1. Recall the different types of stress exerted on rocks. Which type produces folds in rocks?

Divergent Boundaries Because rocks at divergent boundaries experience tensional stresses, the likelihood of folds forming there is low.

Folded rocks are uncommon in which tectonic setting? Hint 1. Recall the various types of stress associated with rock interaction at plate boundaries. Which of these stresses would not produce folds?

Ductile As stress is applied to rocks at depth, ductile deformation induces folds.

Folds exhibit which type of deformation? Hint 1. Recall the different types of deformation that occur in rock. Which type occurs in folds?

Monocline Reactivation of steeply-dipping faults in basement rocks

Formation of a Monocline Which of the following is required for a monocline to form? Hint 1. The uniqueness of monoclines Focus on the specific components of this unique fold. Consider what causes this type of fold to be different from others.

Compression Force Shorten & Thicken the Rock

How will compressional force change a rock body?

Stretch and thin the rock.

How will tensional force change a rock body?

Non-plunging folds look like straight lines at the surface, and plunging folds look like wavy lines.

Imagine a fold has been eroded to a flat surface. In general, how would you know whether this fold is plunging?

Rocks would be youngest on the edges and oldest in the middle.

Imagine an anticline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?

Compressional Force

Part complete Which type of force causes folding?

Dome Because the limbs of the structure associated with the Black Hills all dip away from the center of the hills, the feature is known as a dome.

The Black Hills of South Dakota are a good example of which feature? Hint 1. The limbs of the fold associated with the Black Hills all dip away from the center. Which kind of fold is typified by this structure?

the footwall below and the hanging wall above

What are rocks below and above a fault called?

Factual fractures along which rocks move

What is a fault?

Fault A fracture in a rock along which motion has occurred...

What is a fault?

Syncline a fold shaped like a right-side-up U

What is a syncline?

Anticline - a fold shaped like an upside-down U

What is an anticline?

a fold shaped like an upside-down U

What is an anticline?

a combination of folding and tilting

What produces plunging folds?

Valleys form where rock layers are easily erodible (soft).

Where do valleys tend to form in a landscape? Hint 1. Valleys are low areas, usually between ridges.

Aa Aa is a feature that occurs in lava when it is cooling and the surface is brittle, while it is in the process of flowing.

Which feature is not considered a rock structure? Hint 1. Rocks often undergo brittle and/or ductile deformation to produce a wide variety of structural features.

Compressional Stress The crust is shortened and thickened.

Which of the following is an example of strain produced by compressional stress? Hint 1. Compressional stress results in a rock mass being squeezed, as if in a vise.

Erosion Erosion varies from place to place.

Which of the following statements is true about erosion?

Compressional Stress Convergent

Which tectonic boundary is associated with compressional stress?

Divergent

Which tectonic boundary would have many normal faults associated with it?

Overturned When compressional stress is applied to rocks and one of the limbs is pushed far beyond the vertical, it results in the formation of an overturned fold.

Which term is used to describe a fold in which one limb has been tilted far beyond the vertical? Hint 1. The orientation of this fold would seem to place the layers in one limb atop the same layers on the other limb as you move up through the stratigraphic section.

compressional force

Which type of force causes folding?

Fault Formation tensional force

Which type of force is responsible for normal fault formation?

Normal Strike - Slip Formation shear force

Which type of force is responsible for normal strike-slip formation?

Fault Formation -Reverse compressional force

Which type of force is responsible for reverse fault formation?

Confining Pressure In situations such as deep burial, confining pressure exerts uniform stress in all directions.

Which type of stress on rock is uniform in all directions? Hint 1. Uniform stress can be thought of as many equal forces all acting in the same direction (all inward, all outward, etc).

Differential Stress The influence of stress in a single direction via tension, compression, or shearing produces the most deformation of crustal rocks.

Which type of stress produces most crustal deformation? Hint 1. Think about what causes deformation. Would a rock deform if all the stresses acting on it were in balance?

Tension Where two plates are moving away from each other at a divergent boundary, you would observe tensional stress being exerted on the rocks. This would result in relatively thinner crust along the boundary.

Which type of stress would you expect to find at a divergent boundary? Hint 1. Crustal thinning occurs at divergent boundaries.

Shear Where two plates are sliding horizontally past each other at a transform boundary, you would observe shear stress being exerted on the rocks. Because there is no vertical motion of the plates, the crustal thickness is unchanged.

Which type of stress would you expect to find at a transform boundary? Hint 1. Transform boundaries are "conservative" with respect to crustal thickness, meaning the crust is neither thickened nor thinned at a transform boundary.

Ductile Deformation

causes a permanent change in shape or causes a change of shape that does not return to its original shape after the stress is released.

Elastic Deformation

rocks will change shape due to pressure but return to their original state when pressure is released.