Chapter 14 Convergent Boundaries: Origin of MountainsEarth: An Introduction to Physical Geology

14.1

Multiple-Choice Questions1)

The concept that rocks of the crust and upper mantle are floating in gravitational balance is known as ________.

A)

isotropy B)

isostasy C)

isobration D)

isomonism Answer :

B

2)

According to the crustal, gravitational balance idea, which of the following statements is true?

A)

A mountain range undergoing erosion should uplift slowly. B)

As a continental ice sheet thickens, the land beneath should uplift slowly. C)

A basin being filled with sediments should uplift slowly. D)

The crust is thicker under a low lying plain than under a high standing plateau or mountain range.

Answer :

A

3)

The Valley and Ridge Province of the Appalachian Mountains is characterized by ________. A)

sedimentary strata folded in late Paleozoic time B)

deeply eroded, late Paleozoic, fault-block mountains and valleys C)

stratovolcanoes above a volcanic arc D)

crustal stretching as Africa and Eurasia migrated away from North America Answer :

A

4)

Which of the following best describes the geology of the Pacific coastal regions of western North America including Alaska?

A)

An earlier, continental margin broke apart and the geologically similar fragments were tectonically reassembled.

B)

Geologically different, microcontinent-sized fragments and terranes, formed elsewhere, were tectonically accreted to North America.

C)

A massive subcontinent of old igneous and metamorphic rocks (similar to India) was accreted during late Proterozoic time.

D)

Tightly folded, continental shelf strata were squeezed between North America and the convergent, Bering-Siberian subcontinent.

Answer :

B

5)

A(n) ________ is a thick accumulation of sediments and small, tectonic blocks formed of material scraped off a descending, lithospheric plate.

A)

mass movement complex B)

continental shelf, terrain complex C)

accretionary-wedge complex D)

subterranean-accumulation complex Answer :

C

6)

How were the Ural Mountains (Russia) formed? A)

Large, fault blocks of Archean igneous and metamorphic rocks rose as the former Asian and European plates joined to form Eurasia.

B)

Marine strata in a basin between the former Asian and European plates were squeezed, folded, and uplifted as the two joined to form the Eurasian plate.

C)

Active, normal faulting is elevating large, mountain blocks above the level of the vast plains on both sides of the range.

D)

An active volcanic arc, similar to the present-day Aleutian Islands, rose along the southern edge of the Eurasian plate.

Answer :

B

7)

The ranges of the central and southern Rocky Mountains ________. A)

generally contain thick sections of highly folded, Paleozoic, marine strata B)

developed in response to a continent-continent collision C)

are uplifted, blocks that typically have cores of Proterozoic igneous and metamorphic rocks D)

the Paleozoic and Mesozoic sedimentary rocks were elevated and compressed into tight folds; but the deeper, harder rocks of the continental crust were pulled apart by tensional stresses

Answer :

C

8)

During late Paleozoic time, the tectonic configuration of the Appalachian region in eastern North America was most similar to the ________.

A)

Andean (west) edge of the South American plate B)

areas of Africa and Arabia bordering on the Red Sea C)

Pacific coastal region from southern California to Alaska D)

Tibetan Plateau and the Himalayan Range Answer :

B

9)

Which of the following best characterizes the tectonic development of fault-block mountains?

A)

normal faults; crustal stretching and brittle failure of the upper crust B)

reverse faults; crustal stretching and brittle failure of the lower crust C)

normal faults; crustal shortening and plastic flowage of the upper crust D)

reverse faults; crustal shortening and plastic flowage of the lower crust Answer :

A

10)

The Sierra Nevada, CA, and Teton, WY ranges are examples of ________. A)

fault blocks uplifted by late Tertiary to Quaternary normal faulting B)

folding, compression, and thickening of Paleozoic strata in Jurassic time C)

isostatic uplift of crust overthickened in early Paleozoic time D)

uplifted blocks bounded by Quaternary reverse faults Answer :

A

11)

A good example of a present-day, passive, trailing, continental margin is the ________. A)

north flank of the East Pacific Rise B)

west coast of South America C)

east coast of the Japanese Islands D)

west coast of Africa Answer :

D

12)

An exotic terrane created by a seamount accreted to a continental margin would be composed ________.

A)

of folded, quartz sandstone and shallow water, marine limestone B)

exclusively of granite batholiths and rhyolite welded tuffs C)

mainly of organic-rich, black shales and beach-type sandstones D)

mainly of basaltic lava flows and minor, coralline limestone Answer :

D

13)

The ________ are a geologically old mountain range folded and deformed during the Paleozoic.

A)

Cascades in the northwestern United States B)

Rockies in the western United States C)

Appalachians in the eastern United States D)

Alps in Europe Answer :

C

14)

The ________ have crust about twice as thick as normal. A)

Coast Ranges and Sierra Nevada in California B)

Blue Ridge Mountains in the southeastern United States C)

Himalayan Range and Tibetan Plateau in northern India and southwestern China D)

Basin and Range Province in Arizona and Nevada Answer :

C

15)

The ________ of the Appalachian orogen consists of North American, continental shelf strata deposited prior to the late Paleozoic collision with Africa.

A)

metamorphic and igneous rocks of the Blue Ridge B)

igneous and regionally metamorphosed rocks of the Piedmont C)

Cretaceous and Tertiary strata of the coastal plain and continental shelf D)

folded, sedimentary rocks of the Valley and Ridge Province Answer :

D

16)

The Chulitna terrane, Alaska, is a ________ that consists of interbedded, basaltic, lava flows and deep-water, marine limestones.

A)

piece of the Cenozoic, Alaskan, continental margin volcanic arc B)

piece of the ancient Pacific Ocean floor C)

tectonically deformed and strongly metamorphosed accretionary wedge D)

piece of a batholith and its time-equivalent, stratovolcano complex Answer :

B

17)

The ________ is (are) characterized by terrane accretion that has been active throughout most of Mesozoic and Cenozoic time.

A)

western margin of Africa B)

southern margins of India and Australia C)

western margin of North America D)

western margin of the Mid-Atlantic Ridge Answer :

C

18)

Topographically high-standing, mountainous areas generally ________. A)

are underlain by greater than average thicknesses of lower density, crustal rocks B)

subside rapidly to compensate for erosion C)

have thicker, higher density, mantle rocks beneath them at shallow depths D)

experience rapid erosion that thins the crust and causes the area to subside Answer :

A

19)

Which one of the following is an example of an isostatic movement? A)

stream downcutting following a drop in sea level B)

arching of strata at the center of a dome C)

numerous aftershocks associated with deep-focus earthquakes D)

uplift of areas recently covered by thick, continental ice sheets Answer :

D

20)

Folded limestones that occur high in the Himalayas were originally deposited as sediments in a ________.

A)

marine basin between India and Eurasia B)

Cenozoic fault basin between Africa and Arabia C)

deep ocean trench along the southern margin of India D)

late Paleozoic syncline north of the Tibetan Plateau Answer :

A

21)

Since the early Mesozoic, the ________ has been passive tectonically. A)

western margin of North America B)

western margin of South America C)

southern margin of Eurasia D)

eastern margin in the United States Answer :

D

22)

Accretionary wedges are formed ________. A)

at the edge of the overriding plate facing a subduction zone B)

at the base of a passive continental margin C)

on the oceanic plate side of a transform fault D)

around oceanic plate volcanoes fed by long-lived hot spots in the mantle Answer :

A

23)

The severed, upper part of a Jurassic seamount might occur as a distinctive, small terrane ________.

A)

on a passive-margin continental shelf B)

in an arc of stratovolcanoes far inland from a convergent margin C)

along the boundary between two Precambrian shield areas D)

in an accretionary wedge shoved onto an active, continental margin Answer :

D

24)

The term ________ refers specifically to geologic mountain building. A)

orogneisses B)

orogeny C)

orthogeny D)

orthogonal Answer :

B

25)

Subduction zones include all of the following except for ________. A)

deep ocean trenches B)

forearc basins C)

suture zones D)

volcanic arcs Answer :

C

26)

Backarc regions are characterized by ________. A)

compression B)

shearing C)

uplift D)

extension Answer :

D

27)

Volcanism along a continental arc is dominated by the eruption of ________. A)

basaltic lava flows B)

andesitic lavas and pyroclastic materials C)

rhyolitic pyroclastic materials and lavas D)

all of the above Answer :

B

28)

________ basins are characterized by thick sequences of relatively undeformed sedimentary rocks.

A)

Forearc B)

Backarc C)

Transform fault D)

Evaporite Answer :

A

29)

A(n) ________ is a zone where two continents collide, often preserving slivers of oceanic lithosphere between the colliding plates.

A)

passive margin B)

ophiolite C)

suture D)

terrane Answer :

C

14.2

Word Analysis QuestionsExamine the words and/or phrases for each question below and determine the relationship among the majority of words/phrases. Choose the option which does not fit the pattern.

1)

A) Himalayas B) Andes C) Appalachians D) Alps Answer :

Andes

2)

A) seamount B) deep-ocean trench C) volcanic arc D) forearc Answer :

seamount

3)

A) compression B) fold-and-thrust-belt C) suture D) island arc Answer :

island arc

4)

A) Japan B) Andes C) Appalachians D) Sierra Nevada Answer :

Appalachians

14.3

True/False Questions1)

Folds and thrust faults in the rocks of the Appalachian region formed in late Paleozoic time when Africa collided with North America.

Answer :

TRUE

2)

The Himalayan Mountains and Tibetan Plateau are still rising today as Eurasia slides beneath the Indian subcontinent.

Answer :

FALSE

3)

As the Pleistocene ice sheets in Canada grew and thickened, the crust beneath the ice gradually subsided.

Answer :

TRUE

4)

Uplift generally accompanies erosion of mountain ranges composed of overthickened, low density, crustal rocks.

Answer :

TRUE

5)

Terrane accretion generally occurs along a divergent boundary between a continental plate and an oceanic plate.

Answer :

FALSE

6)

Adjacent terranes accreted to a continent will generally show similar geologic histories for the time before joining and different geologic histories thereafter.

Answer :

FALSE

7)

Accretionary wedges develop along subduction zones where sediments and other rocks are scraped off a descending plate and piled against the leading edge of the overriding plate.

Answer :

TRUE

8)

Volcanic island arcs and granitic, batholithic zones develop along convergent margins on the overriding plate above an oceanic plate sinking into the mantle.

Answer :

TRUE

9)

Soft, easily eroded strata high in a mountain range would suggest that the mountain building occurred long ago, geologically speaking, like that in the Appalachian region along the eastern margin of North America.

Answer :

FALSE

10)

An ophiolite-complex terrane would contain abundant, rhyolitic, volcanic rocks and sandstone.

Answer :

FALSE

11)

Passive, trailing, continental margins typically exhibit normal faults that were active when the original, single continent was rifted.

Answer :

TRUE

12)

Turbidite sandstones with graded bedding would be common on continental shelves associated with trailing, passive, continental margins.

Answer :

FALSE

13)

Overthickened crust continues to slowly rise, even though its thickness is gradually being reduced by erosion.

Answer :

TRUE

14)

Fold-and-thrust-belts are commonly associated with fault-block mountains Answer :

FALSE

14.4

Short Answer Questions1)

The east coast of North America is a good example of a ________ tectonic margin. Answer :

passive

2)

An ________ is a thick accumulation of sediments and small, tectonic blocks composed of material scraped off a descending, lithospheric plate.

Answer :

accretionary wedge

3)

The ________ mountains in North America were formed by a continent-continent collision in the Paleozoic.

Answer :

Appalachian

4)

________ refers to the floatational balance achieved between rocks of the crust, lithosphere, and deeper mantle.

Answer :

Isostasy

5)

The ________ are a young, currently rising mountain range that resulted from continental collision.

Answer :

Himalayas

6)

The ________ mountains in North America are, in large part, a product of the Laramide orogeny.

Answer :

Rocky

7)

Fault-block mountains occur in regions dominated by ________ faulting. Answer :

normal

8)

Any accreted crustal fragment that has a geologic history distinct from that of the adjoining fragments is termed a ________.

Answer :

terrane

14.5

Critical Thinking QuestionsUse complete sentences, correct spelling, and the information presented in Chapter 14 to answer the questions below

1)

Considering the dynamics at convergent plate boundaries where subduction is occurring, how would the angle of the subducting plate (as measured from horizontal) influence the geographic location of the associated volcanic arc? Also, if the angle of a subducting plate changed over time, how would this be expressed by the spatial distribution and ages of volcanic rocks produced by the subduction zoned?

2)

Why would geologic mapping be particularly difficult in a region characterized by accreted terranes? Also, why would the recognition of such terranes in older, deeply eroded areas such as continental shields be important in understanding the geologic history of an area?

3)

Describe the characteristics of regions dominated by fault-block mountains such as the Basin & Range. What is their relationship to plate tectonics and why don't they create large-scale areas of orogenesis like Andean-Type margins or continental collisions?