Ch. 10 Physical Geo Crustal Deformation

Match the fault with the appropriate stress that caused it.

Normal Fault - Tension Reverse Fault - Compression Strike-slip fault - Shear

Match the type of stress to the correct definition.

Tension - forces pull apart from each other Compression - forces move toward each other Shear - forces slide past each other

Look again at the Gigapan image and examine each zone below, then label them with the correct strike & dip symbol. Assume that we are looking towards the north in the image.

Zone 1 - left Zone 2 - right Zone 3 - left Zone 4 - right

The limbs of an anticline will have dip angles pointing ____.

away from each other

The Black Hills of South Dakota is a good example of which type of geologic structure?

dome

Which of the following images is correct for a strike-and-dip symbol for a rock layer trending N 45º W and dipping 23° SW?

23 pointing NW

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

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

________ is the compass direction of the line produced by the intersection of an inclined rock layer with a horizontal plane.

Strike

Which of the diagrams below corresponds to the faulting style you observed in the chalk outcrop?

The hanging wall block in the chalk outcrop is on the right side of the fault plane in the image.

Where are the youngest rocks in a structural basin found?

The youngest rocks of a basin are on top of all the other rock layers In top view, the youngest rocks of a basin are near the center of the basin

What are rocks below and above a fault called?

the footwall below and the hanging wall above

Assume the dolls are each 4 centimeters tall. Measure the extent of displacement by using the height of one of the dolls as your scale. How much displacement (in meters) has occurred? Note that: 1 doll = 4 cm 1 meter = 100 centimeters

0.4 meters

How are reverse faults different from thrust faults? In what way are they similar?

A reverse fault is steeper than a thrust fault; thrust faults have dips that are lower than 45 degrees. Both reverse and thrust faults result from compressional stress.

Interpretation of the folds of this outcrop can provide the geological history of this region. They tell a story about what happened years ago. What is the order of events and the result of stress and deformation? Note that a rock layer is a single layer, which could be overlain or underlain by another layer, but anticlines and synclines are a series of rock layers.

Anticline Younger rock layer on top Older rock layer on bottom Syncline

Refer to the drawing below to review the different types of folds. Now, examine the outcrop in the Gigapan image again. Observe each side, or limb, of each fold. Compare the steepness of each limb's dip to determine whether the fold is symmetrical or asymmetrical. Next, review the statements below, and indicate which are correct for the style of folding present in the Gigapan image.

At least one of the folds in this outcrop is asymmetrical. One side of the anticline dips more steeply than the other.

Which or statement or statements correctly describe brittle deformation and ductile deformation?

Both brittle deformation and ductile deformation are permanent. Brittle deformation describes a rock breaking as a result of stress, whereas ductile deformation describes a rock bending or folding as a result of stress.

________ is the angle of inclination of the surface of a rock unit measured from a horizontal plane.

Dip

Which of the following statements is true about erosion?

Erosion varies from place to place.

Movements along normal faults can produce alternating upthrown and down-dropped fault blocks. What are the names associated with these blocks, respectively?

Horsts and grabens

Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.

Large rifts or valleys, which can often have very large normal faults, are created tensional forces. If a rock undergoes folding and is compressed to form an upward arch, this is a(n) anticline type fold. A trough, or downward fold, called a(n) syncline is formed when a rock is deformed through folding. When a rock is under undue stress and fractures but there is no movement to either side of the fracture, the feature is called a joint. If, however, there is movement, it is called a fault.

How does a monocline form?

Movement along a steep fault in basement rock pushes up a portion of the ductile rock layers above it.

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

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

Rank the following events in order from OLDEST to YOUNGEST in age.

Oldest Sediments are deposited in a horizontal orientation. The sediments are buried and lifted into sedimentary rock. Compressional forces cause the sedimentary rocks to bend into an anticline. Processes of weathering and erosion expose the interior of the anticline. Youngest

What are slickensides?

Polished and striated surfaces made on fault blocks

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

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

Imagine you are out in the field and have to sketch and label the view below. Based on observations from the previous photo, which of the following sketches is the most accurate?

Sketch 5

Assume that this square is a rock that is being subjected to confining pressure. Also assume that the length of the arrows reflects the amount of force in each direction, so the longer the arrow, the more force affecting the rock. How will the size or shape of the square change? Select the choice that best reflects this change.

Square got smaller but stayed the same shape

How does strain differ from stress?

Strain is the change in rock shape that results from stress, which is the force that deforms the rock.

Determine whether each geologic feature is being caused by tensional, compressional, or shear stresses by analyzing the directions of the forces being applied.

Tensional - Normal Fault Compressional - Thrust fault dip angle < 45 deg, Reverse fault dip angle > 45 deg, Folded rocks Shear - Strike-slip fault

Which of the descriptions below accurately describe the three various types of differential stress and the changes they can impart to rock bodies?

Tensional stress, which pulls rock apart in opposite directions, horizontally stretches and lengthens rock bodies Shear stress, which moves one part of a rock body past another, changes rock shape and can break rocks apart Compressional stress, which squeezes rock, generally shortens rocks horizontally and thickens them

Look at the list of terms below regarding anticline and syncline and match them to the sentences they best complete.

The axial plane is the location where a bedrock layer is folded. The sides of a folded bedrock layer are the limbs. The two sides of a fold in a syncline dip toward one another. The two sides of a fold in a anticline dip away one another. The dip will point in the direction in which the rock layer slants. The strike is parallel to the direction of a fold crest and trough.

What is the relative movement along a strike-slip fault? SELECT ALL THAT APPLY.

The dominant displacement is parallel to the strike of the fault. Both blocks of rock move horizontally past each other.

Where do valleys tend to form in a landscape?

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

What produces plunging folds?

a combination of folding and tilting

What is a syncline?

a fold shaped like a right-side-up U

What is an anticline?

a fold shaped like an upside-down U

What does the term plunging fold mean?

a fold that is tilted down into Earth

Which type of force causes folding?

compressional force

Which type of force is responsible for reverse fault formation?

compressional force

What type of deformation is shown in the Gigapan image?

ductile

What is a fault?

fractures along which rocks move

Folds form in ________ temperature-________ pressure environments.

high-; high-

Faults form in ________ temperature-________ pressure environments.

low-; high-

Faults that exhibit both dip-slip and strike-slip movement are called ________ faults.

oblique-slip

The same type of stress that creates anticlines and syncline in some rocks will create ____ faults in rocks that exhibit brittle deformation.

reverse and thrust

____ rock units are most useful when mapping structures like anticlines and synclines.

sedimentary

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

shear force

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

strike-slip fault

From the list of terms below, choose the ones associated with the fault you observed in the Gigapan image.

tensional environment normal fault extension of the crust

Which type of force is responsible for normal fault formation?

tensional force