Mountain building & Mountain building & the evolution of the evolution of continentscontinents

Chapter 20Chapter 20

1. Mountain belts2. Mountain building3. Continental accretion4. Uplift, Basin and Range , Southern

Rocky mountains

Study questionsStudy 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 belts1) Mountain belts

““OrogenyOrogeny”” = mountain building = mountain building

Mountain beltsMountain belts = continuous mountain ranges= continuous mountain ranges

Huge horizontal forces in the crust build mountainsHuge horizontal forces in the crust build mountains

Signs of such forces: folding, faulting, metamorphism, Signs of such forces: folding, faulting, metamorphism, igneous activityigneous activity

Huge horizontal forces in the crust build mountainsHuge horizontal forces in the crust build mountains

Signs of such forces: folding, faulting, metamorphism, Signs of such forces: folding, faulting, metamorphism, igneous activityigneous activity

many “young” mountain belts ( < 100 million years old)

Paleozoic and Precambrian-age mountains (> 250 millionYrs old)

mountain belts usually parallel folded/faulted ridges

sedimentary or volcanic rocks, usually intruded by igneous bodies

- Western Americas- Himalayas (45 million yrs ago)- NW Pacific, etc

- Appalachians- Urals

Fig. 20.1+19

1) Mountain belts1) Mountain belts

2) Mountain building2) Mountain building

Convergent Boundaries

Ocean-ocean boundaries (Aleutian-type)

Ocean-continent boundaries (Andean-type)

Generates avolcanic arc

1st: a passive continental margin (like east coast of US)2nd: turns into an active margin, subduction initiates3rd: deformation, metamorphism: 2 parallel zones: accretionary wedge and volcanic arc

2) Mountain building2) Mountain building

Subduction zones (convergent plate boundaries)

Continental collisions (examples: Himalayas, Appalachians)

Himalayas

Fig. 20.13,14,15

2) Mountain building2) Mountain building

Subduction zones (convergent plate boundaries)

Continental collisions (examples: Himalayas, Appalachians)

Himalayas

Fig. 20.15

2) Mountain building2) Mountain building

Subduction zonesSubduction zones (convergent plate boundaries) (convergent plate boundaries)

Continental collisionsContinental collisions

AppalachiansValley and Ridge Province in Pennsylvania

Fig. 20.4

Formation of the AppalachiansFormation of the Appalachians

3) Continental accretion3) Continental accretion

““Continental accretion”Continental accretion”

Small island arcs or “mini-continents”can be added to continents

Example: Western N. America

Accreted crustal blocks= terranes

Fig. 20.11Fig. 20.12

4. Uplift, Basin and Range, Southern Rockies4. 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.

Fault-block mountain ranges and rift valleys

Basin and RangeBasin and Range

Current uplift or subsidence in the U.S.Current uplift or subsidence in the U.S.

4. Uplift, Basin and Range, Southern Rockies4. Uplift, Basin and Range, Southern Rockies

Sample MCSample MC

Where are the oldest rocks in North America located?

A. in the Appalachian MountainsB. in the Basin and Range provinceC. in the Canadian ShieldD. in the Rocky Mountains

Sample MCSample MC

In which of the following settings were most of the rocks of the interior platform of North America deposited?

A. in a continental riftB. in a deep ocean basinC. in an extensive shallow seaD. in a volcanic island arc

Sample MCSample MC

Why is the North American Cordillera topographically higher than the Appalachians?

A. because the Appalachians have undergone less erosionB. because the Cordillera formed by continent-continent collisionC. because the main orogeny in the Cordillera was more recentD. because the spreading rate of the East Pacific Rise is greater than the spreading rate of the Mid-Atlantic Ridge

Sample MCSample MC

 Which of the following processes is responsible for the topography of the Basin and Range province in western North America?

A. normal faultingB. strike-slip faultingC. thrust faultingD. upwarping

Sample MCSample MC

In which of the following regions is new material currently being added to the crust?

A. Appalachian MountainsB. Canadian ShieldC. Cascade RangeD. Rocky Mountains

Sample MCSample MC

Which of the following mountain belts formed as a result of a collision between two continents?

A. AppalachiansB. HimalayasC. UralsD. all of these

Sample MCSample MC

What type of faults are depicted in the cross section?

A. normal faultsB. strike-slip faultsC. thrust faultsD. cannot tell from the information given

A

B

C