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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
Chapter 10
Deformation, Mountain Building, and the Continents
Table of Contents
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Chapter Outline
Learning Outcomes
Chapter Summary
Lecture Suggestions
Enrichment Topics
Common Misconceptions
Consider This
Key Terms
Internet Sites, Videos, Software, and Demonstration Aids
Chapter Outline
Introduction
LO1 Rock Deformation: How Does It Occur?
LO2 Strike and Dip: The Orientation of Deformed Rock Layers
LO3 Deformation and Geologic Structures
LO4 Deformation and the Origin of Mountains
LO5 Earth’s Continental Crust
Learning Outcomes
After reading this unit, the students should be able to do the following:
LO1 Explain how rock deformation occurs
LO2 Understand strike and dip—the orientation of deformed rock layers
LO3 Identify the types of deformation and geologic structures
LO4 Understand deformation and the origin of mountains
LO5 Describe Earth’s continental crust
Chapter Summary
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Folded and fractured rocks have been deformed or strained by applied stresses.
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Stress is compression, tension, or shear. Elastic strain is not permanent, but plastic strain
and fracture are, meaning that rocks do not return to their original shape or volume when
the deforming forces are removed.
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Strike and dip are used to define the orientation of deformed rock layers. This same
concept applies to other planar features, such as fault planes.
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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
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Anticlines and synclines are up- and down-arched folds, respectively. They are identified
by strike and dip of the folded rocks and the relative ages of rocks in these folds.
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Domes and basins are the circular to oval equivalents of anticlines and synclines, but they
are commonly much larger structures.
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The two structures that result from fracture are joints and faults. Joints may open up, but
they show no movement parallel with the fracture surface, whereas faults do show
movement parallel with the fracture surface.
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Joints are very common and form in response to compression, tension, and shear.
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On dip-slip faults, all movement is up or down the dip of the fault. If the hanging wall
moves relatively down, it is a normal fault, but if the hanging wall moves up, it is a
reverse fault. Normal faults result from tension; reverse faults result from compression.
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In strike-slip faults, all movement is along the strike of the fault. These faults are either
right-lateral or left-lateral, depending on the apparent direction of offset of one block
relative to the other.
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Oblique-slip faults show components of both dip-slip and strike-slip movement.
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A variety of processes account for the origin of mountains. Some involve little or no
deformation, but the large mountain systems on the continents resulted from deformation
at convergent plate boundaries.
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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
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A volcanic island arc, deformation, igneous activity, and metamorphism characterize
orogenies at oceanic–oceanic plate boundaries, whereas orogeny at an oceanic–
continental plate boundary is a result of subduction.
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Some mountain systems are within continents far from a present-day plate boundary.
These mountains formed when two continental plates collided and became sutured.
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Geologists now realize that orogenies also involve collisions of terranes with continents.
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Continental crust is characterized as granitic, and it is much thicker and less dense than
oceanic crust that is composed of basalt and gabbro.
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According to the principle of isostasy, Earth’s crust floats in equilibrium in the denser
mantle below. Continental crust stands higher than oceanic crust because it is thicker and
less dense.
Lecture Suggestions
1. A large sample of “silly putty” can be used to illustrate how a given material can respond
differently to different stresses, or stresses applied at different rates. If a ball of the
material is dropped from a short distance onto a table top, it will bounce, and although a
small amount of the stress, resulting from the impact of the ball with the surface, is
accommodated in a plastic manner (leaving a flat spot on the ball), most of the stress has
been accommodated in an elastic fashion. The material can then be deformed plastically
by squeezing it (compression) or stretching it out (tension), or simply by letting gravity
pull on the ball as it sits on the table. Fracture can result, of course, if the material is
pulled (by tension or shearing) too fast. Point out that even though “silly putty” is not a
rock, rocks can respond in similar fashion under the right circumstances.
2. Strike and dip are difficult to visualize and need to be demonstrated in class. To illustrate
strike, as well as apparent and true dip, stack some books and prop them at an angle. Let
the binding’s trace be the strike and the cover be the bed’s dip surface. Take a pencil and
orient it on the dip surface (cover), so it is parallel to strike (the binding). Now, slowly
rotate the pencil, so its eraser end remains fixed on the dip surface and its point moves
away from the dip surface in a horizontal plane, until it lies perpendicular to the strike
(binding edge). Notice that the distance between the pencil point and the dip surface
(book cover) increases from zero (when the pencil is parallel to strike) to a maximum
value, when it is perpendicular to the strike. The angle between the eraser and the
pencil’s projection (or its shadow from an overhead light) on the cover will increase from
zero to some maximum value. These are dip or inclination angles, and the maximum
value is that of the true dip.
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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
3. Students are likely to remember hanging wall and footwall if they are told that the
hanging wall is characterized as that wall from which a geologist could only hang (as
opposed to walk) and the footwall as that wall that would be beneath a geologist’s feet.
4. Once they can recognize the hanging wall and footwall, it may help the students
remember the types of dip-slip faults from the acronym FUN. This stands for “Footwall
(moved) Up, = Normal” fault. Obviously, the other type is HUR (“Hanging Wall Up =
Reverse”).
5. Ask students to compare and contrast the types of geologic features, structures, and
activity that occur on continental–continental, continental–oceanic, and oceanic–oceanic
convergent plate boundaries. Also, compare and contrast the geologic features, structures,
and activity along divergent, convergent, and transform plate boundaries.
6. The terms and structures of anticlines and synclines can be more readily understood if it
is noted that cline means slope and anti means opposite or away from, while syn means
together or toward.
7. A three-layered peanut butter and jelly sandwich, cut so as to illustrate a fault, can be
used to demonstrate the types of forces and resulting structures that form along
convergent, divergent, and transform boundaries.
Enrichment Topics
Topic 1. Devastating Indian Earthquakes. Plate tectonics is responsible for earthquakes in
India in which tens of thousands of people die. In January 2001, more than 10,000 people were
killed in an intraplate earthquake on the Indian subcontinent. The Indian subcontinent is
driving ever northward into Asia, so even where the plates don’t meet, weak spots are prone to
earthquakes. India has suffered five such earthquakes since 1965; the January 2001 quake was
on an ancient rift that originated when India separated from Gondwana 150 million years ago.
At even more risk is the northeastern edge of the plate, where it is colliding with Asia and the
strain is building very fast. ScienceNOW, January 29, 2001.
Topic 2. Birth of a Mountain Range, But When? There are two camps in the debate on
when the Sierra Nevada Mountains rose: One says that it was between 60 and 40 million years
ago when a subducted ocean plate slid beneath the continent and raised it up. The other thinks
that it occurred between 5 and 3 million years ago when a large chunk of crust broke off from
beneath the continent, melted, became buoyant, and caused the range to rise. One way of
trying to determine when the range rose is to look at hydrogen isotopes of ancient raindrops to
distinguish the height of the cloud from which the drop fell. This technique favors the first
explanation, that the Sierra Nevada Mountains rose about 50 million years ago, but the results
are still controversial. ScienceNOW, July 6, 2006.
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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
Common Misconceptions
Misconception: Rocks are solid, permanent, unmovable, and undeformable, as shown in such
expressions as “solid/hard as a rock,” “like a rock,” “I am a rock,” etc.
Fact: Rocks respond to stresses just as other solid objects do, and given sufficient stress
conditions, which may include a long enough interval of time, rocks will deform like a
plastic, taking on new orientations, shapes, and dimensions.
Consider This
1. What will happen to the western coast of California in 30 or 40 million years as the result
of movements along the San Andreas Fault Zone?
2. Locate the shield areas of each of the continents.
3. If orogenesis is typically associated with the active margins of continents and the Rocky
Mountains are relatively young and not the product of suturing of two continents, how
can the mid-continent location of the Rocky Mountains be explained by plate tectonic
theory?
4. What type of forces and geologic structures dominate the northern Rocky Mountains?
Which dominate the middle Rocky Mountains?
Key Terms
anticline
basin
compression
continental accretion
deformation
dip
dip-slip fault
dome
elastic strain
fault
fault plane
fold
footwall block
fracture
geologic structure
gravity anomaly
hanging wall block
isostatic rebound
joint
monocline
normal fault
oblique-slip fault
orogeny
plastic strain
principle of isostasy
reverse fault
shear stress
strain
stress
strike
strike-slip fault
syncline
tension
terrane
thrust fault
Internet Sites, Videos, Software, and Demonstration Aids
Internet Sites
1. Himalayas: Where the Earth Meets Sky: library.thinkquest.org/10131/
The formation of the Himalaya Mountains.
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Instructor’s Manual
GEOL
Chapter 10
Deformation, Mountain Building, and the Continents
Videos
1. Natural Landscapes of North America. Insight Media (1999, 21 min.)
The eight major geologic regions of North America with descriptions of the natural
forces that created and continue to shape them.
2. Mountain Building and Continents. Insight Media (1999, 18 min.)
The evolution of the continents and major mountain belts.
3. Mountains and Mountain-Building Processes. Insight Media (2000, 23 min.)
Mountain-building processes in several mountain ranges around the world depicted by
graphics and live-action footage.
4. Earth Revealed. Annenberg Media: http://www.learner.org/resources/series78.html
(1992, 30 min., free video):
 #7: Mountain Building. Animations reveal how mountains are built and how they
erode with emphasis on plate tectonics, the rock cycle, and other processes.
5. Before the Mountains. AAPG Bookstore DVD (1987, 29 min.)
The sedimentary rocks that came before the Rocky Mountains.
6. Birth of the Rockies. AAPG Bookstore DVD (1987, 28 min.)
The thrust sheets that form the Rockies.
Slides
1. GeoPhoto Publishing, 35 mm transparencies or digital images:
http://geophotopublishing.com/
 Crustal Deformation
2. Educational Images Slide Sets: http://www.educationalimages.com/cg120001.htm
 Sediments, Faults, Unconformities
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