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Chapter 20
Mountain building & the evolution of
continents
1. Mountain belts
2. Mountain building
3. Continental accretion
4. Uplift, Basin and Range , Southern
Rocky mountains
Study questions
What is the geologic history of the Basin and Range
province and southern Rocky mountains?
What is an accreted terrane and where do they originate?
What is the connection with plate tectonics?
What is the geologic history of the Himalayas and
Appalachians?
1) Mountain belts
“Orogeny” = mountain building
Mountain belts = continuous mountain ranges
 Huge horizontal forces in the crust build mountains
 Signs of such forces: folding, faulting, metamorphism,
igneous activity
1) Mountain belts
 many “young” mountain
belts ( < 100 million years
- Western Americas
old)
- Himalayas (45 million yrs ago)
- NW Pacific, etc
Paleozoic and
Precambrian-age
mountains (> 250 million
Yrs old) - Appalachians
- Urals
 mountain belts usually
parallel folded/faulted
ridges
 sedimentary or volcanic
rocks, usually intruded by
igneous
bodies
Fig. 20.1+19
2) Mountain building
Convergent Boundaries
Ocean-ocean boundaries (Aleutian-type)
Generates a
volcanic arc
Ocean-continent boundaries (Andean-type)
1st: a passive continental margin (like east coast of US)
2nd: turns into an active margin, subduction initiates
3rd: deformation, metamorphism: 2 parallel zones:
accretionary wedge and volcanic arc
2) Mountain building
Subduction zones (convergent plate boundaries)
Continental collisions (examples: Himalayas, Appalachians)
Himalayas
Fig. 20.13,14,15
2) Mountain building
Subduction zones (convergent plate boundaries)
Continental collisions (examples: Himalayas, Appalachians)
Himalayas
Fig. 20.15
2) Mountain building
Subduction zones (convergent plate boundaries)
Continental collisions
Appalachians
Valley and Ridge
Province in
Pennsylvania
Fig. 20.4
Formation of the Appalachians
3) Continental accretion
“Continental accretion”
Small island arcs or “mini-continents”
can be added to continents
Accreted crustal blocks= terranes
Example: Western N. America
Fig. 20.11
Fig. 20.12
4. Uplift, Basin and Range, Southern Rockies
Fig. 20.5
See Fig. 20.6
Northern Rocky Mountains, British Columbia
Deformed sedimentary rock from continental shelf deposits displaced by
low angle thrust faults toward the interior of Canada.
Basin and Range
Fault-block mountain ranges and
rift valleys
4. Uplift, Basin and Range, Southern Rockies
Current uplift or subsidence in the U.S.
Sample MC
Where are the oldest rocks in North America located?
A.
B.
C.
D.
in the Appalachian Mountains
in the Basin and Range province
in the Canadian Shield
in the Rocky Mountains
Sample MC
In which of the following settings were most of the rocks of the interior platform of
North America deposited?
A.
B.
C.
D.
in a continental rift
in a deep ocean basin
in an extensive shallow sea
in a volcanic island arc
Sample MC
Why is the North American Cordillera topographically higher than the
Appalachians?
A. because the Appalachians have undergone less erosion
B. because the Cordillera formed by continent-continent collision
C. because the main orogeny in the Cordillera was more recent
D. because the spreading rate of the East Pacific Rise is greater than the
spreading rate of the Mid-Atlantic Ridge
Sample MC
Which of the following processes is responsible for the topography of the Basin and
Range province in western North America?
A.
B.
C.
D.
normal faulting
strike-slip faulting
thrust faulting
upwarping
Sample MC
In which of the following regions is new material currently being added
to the crust?
A.
B.
C.
D.
Appalachian Mountains
Canadian Shield
Cascade Range
Rocky Mountains
Sample MC
Which of the following mountain belts formed as a result of a collision between two
continents?
A.
B.
C.
D.
Appalachians
Himalayas
Urals
all of these
Sample MC
What type of faults are depicted in the cross section?
A.
B.
C.
D.
normal faults
strike-slip faults
thrust faults
cannot tell from the information given
B
A
C