Folds, Faults: Stratigraphy, continued

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Assignments	Chernicoff, Folds, Faults and Mountains, ch. 9 (all).
Reminders	Review notes for ch. 8 on stratigraphy, knowledge of which is assumed for this chapter. Check out the new information posted in the hallway exhibit.... Can you identify the "Bert" of the month?

Lesson Outline

Read the assigned portions of each chapter. Study the illustrations. Focus your attention on the vocabulary terms found in the following notes.

I. Stressing and Straining Rocks

1. Introduction
   1. The force applied to a rock per unit area is called "Stress."
      1. "Compression" is a type of stress caused by the pushing together of rocks.
      2. Stress caused by the pulling apart of rocks is called "tension."
      3. The stress on rocks forced past one another in parallel but opposite directions is known as "shearing."
   2. The change in the shape of a rock due to stress is called "Strain."
2. Types of deformation (model with Silly Putty)
   1. Temporary:
      1. In "Elastic deformation," a strained rock regains its original shape after stress is removed.
   2. Permanent:
      1. "Brittle failure" is when a rock ruptures when it exceeds its yield point.
      2. "Plastic deformation" is an irreversible change in shape or volume when a rock is stressed past its yield point.
3. Deformed rocks in the field
   1. Most apparent in sedimentary rocks
   2. Importance:
      1. Determines other past geological events
      2. Locates specific natural resources
   3. Rock orientation:
      1. The compass direction of the imaginary line forming the intersection between a rock structure and the Earth's surface is called the rock's "strike."
      2. The angle at which a rock structure is inclined relative to the horizontal plane is referred to as the "dip."

II. Folds

1. Longitudinal
   1. Caused by compression
   2. "Synclines" are concave, troughlike folds in rock strata.
   3. "Anticlines" are convex, archlike folds in rock strata.
   4. The "Axial plane" is an imaginary plane that divides a fold into two nearly equal halves.
   5. Symmetrical vs. asymmetrical
   6. overturned
   7. recumbent
   8. plunging
2. Nonlinear
   1. A structural "Dome" is a round or oval-shaped bulge on the Earth's surface that, in cross-section, resembles an anticline.
   2. A structural "Basin" is a bedrock depression that, in cross-section, resembles a syncline.
   3. Occur within plates, result from vertical forces such as upwelling magma
   4. Geographic examples

III. Faults

1. Introduction
   1. Fractures caused by a variety of stresses
   2. "Faults" are rock fractures along which marked relative movement has occurred.
      1. Fault blocks
      2. Fault plane
2. Types of faults
   1. In "Strike-slip" faults, fault-block movement is relatively horizontal, parallel to the strike of the fault plane.
      1. Caused by shearing stress
      2. Example: San Andreas fault
   2. In "Dip-slip" faults, fault-block movement is relatively vertical, parallel to the dip of the fault plane, causing steps in the landscape.
      1. Hanging wall
      2. Foot wall
      3. Normal faults
         1. Hanging wall moves downward
         2. Caused by tension
         3. Occurs at mid-ocean ridges and continental rifts
         4. Grabens are depressions formed when a fault-block drops in between normal faults.
         5. Horsts are the blocks that remain above on either side of a graben.
      4. Reverse faults
         1. Hanging wall moves upward
         2. Caused by compression
         3. Occurs at convergent plate boundaries
         4. Thrust faults if at low, nearly horizontal angles

IV. Building Mountains

1. Mountain building is called "orogenesis."
2. Types and processes of mountain-building
   1. Volcanic mountains
   2. "Fault-block" mountains are bounded on at least one side by high-angle normal faults.
      1. Description
      2. Basin and Range province
   3. "Fold and thrust" mountains form where continental collisions cause exceptionally high mountain systems.
      1. Description
      2. Examples
   4. "Upwarped mountains" are formed when a large area of the Earth's crust is gently bent into broad regional uplifts without much apparent rock deformation.
      1. Description
      2. Adirondack mountains
3. Remnants of eroded and weathered mountains are called continental ____________.
4. Mountain building on other planets
   1. Lunar mountains caused by meteoritic impacts
   2. Martian mountains caused by volcanism
   3. Venetian mountains caused by Earth-like processes

Reading Focus Questions

Be prepared to answer any of these questions should they occur on a quiz or on the final exam.

1. In geology, stress refers to
   1. how you feel right now
   2. stretching of a rock unit
   3. compression of a rock unit
   4. any deformation of a rock unit
   5. forces that might cause deformation of a rock unit
2. In geology, strain refers to
   1. forces that might cause deformation of rock
   2. temporary deformation of rock due to stress
   3. permanent deformation of rock due to stress
   4. deformation of rock due to stress, either temporary or permanent
3. Rocks in which elastic deformation occurs:
   1. return to their original shape when the stress is released
   2. remain in their deformed shape when the stress is released
   3. become fractured but retain their original shape
   4. show no response to stress
4. Rocks in which plastic deformation occurs:
   1. return to their original shape when the stress is released
   2. remain in their deformed shape when the stress is released
   3. become fractured but retain their original shape
   4. show no response to stress
5. The strike and dip of a rock refer to:
   1. the directions in which a rock points
   2. the orientation of a rock unit in relation to neighboring rock units
   3. the orientation of a rock unit in relation to the surface of the Earth
   4. the orientation of only the exposed surface of a rock
6. Mapping the strike and dip of all the rock units in a region is important because:
   1. it shows the location, elevation, and slope gradient of all the hills and valleys.
   2. it shows the three-dimensional subsurface form of rock units barely visible at the surface.
   3. it shows the locations of all the outcroppings of rocks.
   4. it shows the points at which stress was applied to each of the rock units.
7. Which of the following pairs of statements about anticlines and synclines are both true?
   1. Anticlines are caused by compressive stress, while synclines are caused by tensional stress.
   2. In anticlines, the oldest rocks are in the center; in synclines, the youngest rocks are in the center.
   3. An anticline is present wherever there is a hill; a syncline is present wherever there is a valley.
   4. Anticlines are a result of plastic deformation, whereas synclines are a result of elastic deformation.
8. A fold in which the axial plane is horizontal with the surface of the Earth is a(n):
   1. asymmetrical fold
   2. overturned fold
   3. recumbent fold
   4. plunging fold
9. The San Andreas fault is an examle of a:
   1. strike-slip fault
   2. thrust fault
   3. normal fault
   4. none of the above
10. A normal fault occurs as a result of:
    1. tensional stress, and the hanging wall moves down relative to the footwall.
    2. tensional stress, and the hanging wall moves up relative to the footwall
    3. compressive stress, and the hanging wall moves down relative to the footwall
    4. compressive stress, and the hanging wall moves up relative to the footwall
11. A thrust fault is the result of:
    1. tensional stress, and the hanging wall moves down relative to the footwall.
    2. tensional stress, and the hanging wall moves up relative to the footwall
    3. compressive stress, and the hanging wall moves down relative to the footwall
    4. compressive stress, and the hanging wall moves up relative to the footwall
12. The rocks of which mountains are composed are older than the mountains themselves in all types of mountains EXCEPT:
    1. fault-block mountains
    2. fold-and-thrust mountains
    3. volcanic mountains
    4. upwarped mountains
13. Which of the following statements about specific mountainous areas is NOT true?
    1. The island of Hawaii, the largest mountain on Earth, is a fold-and-thrust mountain.
    2. The Basin and Range province of western United States consists of fault-block mountains.
    3. The Cascade Mountains of Washington and Oregon are volcanic mountains.
    4. The Adirondacks of New York are upwarped mountains.
14. Fault-block mountains are characterized by:
    1. vast upwarped regions
    2. distinctive reverse or thrust faults
    3. high-angle normal faults
    4. thrust faulted and folded marine sediments
15. Upwarped mountains are characterized by:
    1. intense folding and faulting
    2. rugged and extremely high mountain peaks
    3. numerous series of synclines and anticlines
    4. almost no rock deformation
16. Mountains on the Moon probably formed as a result of:
    1. meteoroid impacts
    2. volcanism
    3. differences in crustal density
    4. crustal stretching resulting in fault-block mountains
17. Mountains on Mars probably formed as a result of:
    1. meteoroid impacts
    2. volcanism
    3. differences in crustal density
    4. crustal stretching resulting in fault-block mountains