Geology Ch. 11 Notes – Mountain Building
Objectives:
1. Identify the factors that determine the strength of a rock and how it will deform.
2. Explain how rocks permanently deform.
3. Distinguish among the types of stresses that affect rocks.
4. List the three main types of folds.
5. Identify the main types of faults.
6. Explain how mountains are classified
7. Compare folded mountains and fault-block mountains
8. Describe the formation of a dome.
9. Identify the type of mountains associated with convergent plate boundaries
10. Distinguish between mountains formed by ocean-ocean convergence and
mountains formed by ocean-continental convergence.
11. Identify the type of mountains associated with divergent plate boundaries
12. Explain how isostatic adjustment is involved in mountain formation
11.1 Rock Deformation
1. Factors Affecting Deformation
 Factors that influence the strength of a rock and how it will deform include
temperature, confining pressure, rock type, and time.
• __________________is a general term that refers to all changes in the original
shape and/or size of a rock body.
- Most crustal deformation occurs along plate margins.
• ___________is the force per unit area acting on a solid.
• _________is the change in shape or volume of a body of rock as a result of stress.
 Temperature and Pressure
• Rocks deform permanently in two ways: brittle deformation and ductile
deformation.
- ________deformation is the fracturing of an object once its strength is
exceeded
- ________deformation is a type of solid state flow that produces a
change in the size and shape of an object without fracturing the object.
 Rock Type
• Mineral _____________of a rock also greatly affect how it will deform.
 Time
• Forces that are unable to deform rock when first applied may cause rock to flow if
the force is maintained over a ________________of time.
2. Types of Stress
 The three types of stresses that rocks commonly undergo are tensional stress,
compressional stress, and _________________________
3. Folds
 Anticlines
•
________________are most commonly formed by the upfolding, or arching, of
rock layers.
 Synclines
• __________________are linear downfolds in sedimentary strata.
• Synclines are often found in association with anticlines.
 Monoclines
• __________________are large step-like folds in otherwise horizontal
sedimentary strata.
4. Faults
 Normal Faults
• _______________occur when the hanging wall block moves down relative to the
footwall block.
 Reverse Faults and Thrust Faults
• _______________are faults in which the hanging wall block moves up relative to
the footwall block.
-_________________ are reverse faults with dips less than 45o.
5. Folds
 Strike-Slip Fault
• ________________are faults in which the movement is horizontal and parallel to
the trend, or strike, of the fault surface.
 Joints
- Joints are fractures along which_______ appreciable movement has occurred.
11.2 Types of Mountains
1. Folded Mountains
 Mountains are classified by the dominant processes that have formed them.
• _________________is the collection of processes that result in the forming of
mountains.
 Folded Mountains
• Mountains that are formed primarily by folding are called _____________
2. Fault-Block Mountains
 Large-scale normal faults are associated with structures called fault-block
mountains.
• ____________________are formed as large blocks of crust are uplifted
and tilted along normal faults.
• ______________are formed by the downward displacement of faultbounded blocks.
• ________________are elongated, uplifted blocks of crust bounded by
faults.
3. Domes and Basins
 When upwarping produces a circular or elongated structure, the feature is called a
dome.
• _________________are circular or elongated structures formed by uplifting of
the underlying basement rock.
11.3 Mountain Formation
1. Mountain Building at Convergent Boundaries
 Most mountain building occurs at convergent plate boundaries. Colliding plates
provide the compressional forces that fold, fault, and metamorphose the thick layers of
sediments deposited at the edges of landmasses.
 Ocean-Ocean Convergence
• Ocean-ocean convergence mainly produces_____________________.
 Ocean-Continental Convergence
• The types of mountains formed by ocean-continental convergence are volcanic
mountains and ____________________________
• An __________________________is the accumulation of different sedimentary
and metamorphic rocks with some scraps of ocean crust.
 Continental-Continental Convergence
• At a convergent boundary between two plates carrying continental crust, a
collision between the continental fragments will result and form
___________________
2. Mountain Building at Divergent Boundaries
 The mountains that form along ocean ridges at divergent plate boundaries are
___________________________________
3. Non-Boundary Mountains
 Not all mountains are formed by plate boundaries. Some are formed by hot
spots or regional extension or stretching.
4. Continental Accretion
 ________________is a process that occurs when crustal fragments collide with
and stay connected to a continental plate.
 Terranes
• _________________are any crustal fragments that have a geologic history
distinct from that of the adjoining fragments.
-Terranes occur along the Pacific Coast.
5. Principles of Isostasy
 Isostatic Adjustment for Mountains
• _______________is the concept that Earth’s crust is floating in gravitational
balance upon the material of the mantle.
• Because of isostasy, deformed and thickened crust will undergo regional uplift
both during mountain building and for a long period afterward.
• _________________is the process of establishing a new level of gravitational
equilibrium.
Definitions:
1. deformation: general term for the process of folding, faulting, shearing,
compression, or extension of rocks as a result of various natural forces.
2. stress: the force per unit area acting on a solid.
3. strain: the change in shape or volume of a body of rock as a result of stress.
4. anticline: a fold in sedimentary strata resembling an arch
5. syncline: a downfold in sedimentary strata, the opposite of an anticline
6. monocline: a large step-like fold in otherwise horizontal sedimentary strata
7. normal fault: a fault in which the rock above the fault plane has moved down
relative to the rock below as a result of tensional forces.
8. reverse fault: a fault in which the material above the fault plane moves up in
relation to the material below as a result of compression
9. thrust fault: a reverse fault with a dip less than 450, normally about 100 - 150
10. strike-slip fault: a fault along which the movement is horizontal and parallel o the
trend of a fault
11. orogenesis: the process of building mountains
12. folded mountain: a mountain created primarily by compressional stresses, which
create folds in the rock
13. fault-block mountain: a mountain formed when large blocks of crust are tilted,
uplifted, or dropped between large normal faults
14. graben: a valley formed by the downward displacement of a fault-bounded block
15. horst: an elongated uplifted block of crust bounded by faults
16. accretionary wedge: a large wedge-shaped mass of sediment that accumulates in
subduction zones; here sediment is scraped from the subducting oceanic plate and
accreted to the overriding crustal block
17. accretion: process that occurs when crustal fragments collide with and stay
connected to a continental plate
18. terrane: a crustal block bounded by faults, whose geologic history is distinct from
the histories of the surrounding rock
19. isostasy: the concept that Earth’s crust is floating in gravitational balance upon the
material of the mantle
20. isostatic adjustment: process of establishing a new level of gravitational
equilibrium
21. dip: the angle that fold or fault makes with the horizontal; flat rock layers have a
dip of 00
22. compressional stress: squeezing rock together causing the material to shorten
23. tensional stress: pulling rock apart causing the rock to lengthen
24. shear stress: material is distorted with no change in volume