Deck 4: Volcanoes and Volcanic Processes

Question 1

Accretionary wedges are formed .

A) at the base of a passive continental margin
B) at the edge of the overriding plate against a subduction zone
C) on the oceanic plate side of a transform fault
D) around submarine volcanoes fed by long- lived hot spots in the mantle

Answer 1

B

Question 2

What mechanism is proposed for Cretaceous subsidence of the Canadian and American prairies?

A) A subducting slab detaches from the trailing lithosphere, creating a downward flow that drags the base of the overriding continent with it.
B) An underlying mantle plume suddenly quit, cooled, and subsided.
C) A former broad monocline under the prairies eventually flattened out.
D) A large Cretaceous meteorite impacted the prairies, the evidence for which has yet to be found.

Answer 2

A

Question 3

Thick blocks of crust carried toward a subduction zone .

A) can get sliced off the descending slab and transferred to the accretionary continental margin as an accreted terrane
B) get eroded, contributing a greater than usual volume of sediments to the trench at that point
C) get uplifted to become an island on the oceanward side of the trench
D) cause the subduction zone to stop or reverse and begin subducting the other way

Answer 3

A

Question 4

What supercontinent drifted apart in the Proterozoic to form the first extensional phase of the Appalachian orogen?

A) Pangaea
B) Laurasia
C) Gondwanaland
D) Rodinia

Question 5

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

A) along the boundary between two Precambrian shield areas
B) in an accretionary wedge shoved onto an active, continental margin
C) on a passive- margin continental shelf
D) in an arc of composite cone volcanoes far inland from a convergent margin

Question 6

Mountains without active volcanic arcs are associated with a(n) margin.

A) continent- continent
B) divergent
C) ocean- ocean
D) continent- ocean

Question 7

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

A) Dunnage Zone (Taconic phase)
B) Avalonia bock (Acadian phase)
C) Humber Zone (Valley and Ridge in USA) of folded sedimentary rocks on the eastern edge
D) Meguma Zone

Question 8

Compared to normal continental crust in the middle of a stable craton, the crust under mountain belts can be .

A) about five times as thick at more than 160 km
B) about twice as thick at more than 70 km
C) about three times as thick at more than 100 km
D) about half as thick at less than 18 km

Question 9

How were the Ural Mountains (Russia) formed?

A) An active fold and thrust belt is forming as Asia and Europe continue to converge and buckle the crust along an old tectonic suture zone.
B) Kilometres of marine strata, originally deposited in a basin between the former Asian and European plates, were squeezed, folded, and uplifted as the two collided and joined to form the Eurasian plate.
C) Normal faulting from a modern continental rift is elevating large mountain blocks above the level of the vast plains on both sides of the range and giving rise to a volcanic mountain chain.
D) A large dome of Archean igneous and metamorphic rocks rose up as the Eurasian plate became situated over a mantle plume.

Question 10

What happens as the crust isostatically rises during or following a mountain building episode?

A) The deformed strata experience regional uplift.
B) The mantle flows out of the way to compensate for the rising crust.
C) The root continues to grow to compensate for the increasing elevation.
D) Folding and thrusting continue, to accommodate the increased uplift.

Question 11

What did the earliest continental crust resemble?

A) foreland and intracratonic basins with mature quartz- rich sandstones
B) giant protocontinents of silica- rich magmas formed from the early differentiation of Earth into crust, mantle, and core
C) basaltic rift zones like East Africa
D) andesitic island arcs like the Aleutians

Question 12

When a subduction zone is established under the edge of a continent, this gives rise to an accretionary wedge, a volcanic arc, and compressional features farther inland that is called

A) a passive
B) an Andean
C) an Aleutian
D) a Himalayan

Question 13

Mountain belts formed from folded marine sediments by continent- continent collision, include

A) NE edge of Indian Ocean
B) Appalachians and Caledonians
C) East African rift
D) European Alps

Question 14

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

A) continental shelf, terrain complex
B) accretionary- wedge complex
C) subterranean- accumulation complex
D) mass movement complex

Question 15

What is the evidence that the interior of North America experienced major subsidence during the Cretaceous?

A) Petrified walrus tusks were discovered under Calgary.
B) Ophiolite sequences are found in the Canadian prairies.
C) Failed mid- ocean rifts occur in southern Alberta.
D) Sea water invaded much of the continent in which marine sedimentary rocks formed.

Question 16

Which statement best describes an intracratonic basin?

A) synonymous with meteorite crater
B) a circular syncline that developed in the Canadian Rockies
C) a sag pond in the Fraser delta
D) circular bowl- shaped depressions that develop well within continental interiors

Question 17

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

A) A mountain range undergoing erosion should uplift slowly.
B) The crust is thicker under a low lying plain than under a high standing plateau or mountain range.
C) As a continental ice sheet thickens, the land beneath should uplift slowly.
D) A basin being filled with sediments should uplift slowly.

Question 18

The world's highest mountain belts result from convergent plate margins.

A) ocean- ocean
B) accretionary
C) continent- continent
D) transform

Question 19

As new layers of sedimentary or volcanic rock are added to the crust the .

A) thickness increases faster than the elevation
B) elevation stays the same but the thickness increases
C) elevation increases by an equal amount to the thickness
D) elevation increases faster than the thickness

Question 20

The concept of includes the idea that crustal rocks are floating in a kind of gravitational balance and that their elevation depends on their density contrast to the underlying upper mantle.

A) isostasy
B) subsidency
C) isotropy
D) orogeny

Question 21

Prolonged convergence across Aleutian- type margins can result in the .

A) subduction of the volcanic arc
B) complete destruction of both oceanic plates
C) thinning of the lithosphere under the arc
D) development of thick, continental- type crust

Question 22

The is the global tectonic cycle that rifts supercontinents, developes extensive passive margins, opens ocean basins, closes ocean basins, creates new island arc or Andean crustal orogens, and finally builds new collisional mountain belts as the ocean completely closes to make a new supercontinent.

A) Wilson Cycle
B) Seafloor Shake Up
C) Wegnerian Break Up
D) Convective Conga

Question 23

What is the explanation for the rugged mountain and valley topography of the Basin and Range, some 1600 km inland of a plate boundary?

A) Recent terrane accretion moved the coastline westwards from the Colorado- Utah border as the ranges formed.
B) Doubling of the crustal thickness in the past few million years has occurred due to intense thrusting and folding inboard of the San Andreas Fault.
C) A series of multiple subduction zones were all active and closed up about the same time.
D) Low density hot mantle rock has upwelled to hold up ordinary crust to greater than normal elevations.

Question 24

A(n) plate margin commonly evolves from a divergent one.

A) passive
B) transform
C) offshore
D) shallow ramped

Question 25

Most of mainland Alaska, over half of B.C. and the Yukon, and most of Washington, Oregon, Nevada and California are .

A) the geologic equivalents of cratonic stratigraphy found all across North America, but these have been intensively deformed by episodes of convergent margin mountain building in Mesozoic and Cenozoic time
B) an Andean style arc complex, of intermediate and felsic plutonics and volcanics, that formed in Cenozoic time by subduction of Pacific plates beneath North America
C) accreted terranes transported to the north from more equatorial regions, including: Paleozoic through Mesozoic seafloor, island arcs, submarine deposits, and displaced continental fragments
D) tectonically deformed and strongly metamorphosed Early Precambrian accretionary wedge deposits from the earliest, west coast, active margin

Question 26

What observation or interpretation concerning the Himalayas did not ultimately lead to our current understanding about the structure of mountains belts?

A) George Airy's hypothesis that lighter, thicker mountain roots displace denser mantle rocks
B) J. H. Pratt's estimate that, for a flat lower crustal boundary (Moho), the mountains should have deflected the plumb bob 3 times as much as was actually observed
C) Sir George Everest's topographic triangulation survey that placed two towns 150 metres too close together because of the deflection of the vertical "plumb line" by the mass of the mountains
D) The original GPS survey by Nicola Tesla that showed the convergence of India against the Tibetan Plateau was less than expected for seafloor spreading rates.

Question 27

Which of the following geologic products or processes is not a result of mountain building?

A) subsided sedimentary basins in the middle of continental cratons
B) building of a deep sea fan of turbidites offshore from a convergent continent- ocean margin
C) downdropped extensional grabens with playa lakes
D) exposure of belts of high pressure, Precambrian, igneous and metamorphic rocks within continental shield areas

Question 28

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

A) Cascades in the northwestern U.S. and southwestern B.C.
B) Alps in Europe
C) Appalachians of eastern North America
D) Canadian Rockies

Question 29

The rock sequences and mountainous topography of the northern portion of the Appalachian Mountains .

A) is made up of extinct composite cone volcanoes and massive intrusions formed above a Late Precambrian subduction zone
B) were barged across the Atlantic by homesick Scottish immigrants during the Highland Clearances
C) was made up mainly of Late Proterozoic, passive margin sedimentary strata that weren't deformed until the break up of Pangaea in the Late Carboniferous
D) consist of up to six different accretionary sequences, plastered onto the eastern margin of North America during the closing of the Iapetus Ocean over several stages of tectonic convergence between the Cambrian and Carboniferous

Question 30

Between the original Proterozoic rifting of Rodinia and the Late Paleozoic rifting or Pangaea, how much "real estate" was added to the North American continent?

A) the width of Iapetus Ocean, thousands of km
B) the entire width of the Appalachian Orogen, St. Lawrence Seaway through Nova Scotia, 600- 800 km
C) only Newfoundland and Labrador
D) everything from Ontario to Alberta

Question 31

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

A) arching of strata at the centre of a dome
B) stream downcutting following a drop in sea level
C) numerous aftershocks associated with deep- focus earthquakes
D) uplift of areas recently covered by thick, continental ice sheets

Question 32

One piece of evidence for the substantial compression accompanying terrane accretion in B.C. and the Yukon is .

A) Paleozoic subsidence in the Williston Basin of Saskatchewan and Manitoba
B) Pleistocene folds in the offshore crust of the Pacific plate
C) Pleistocene uplift and erosion in the Canadian Shield of the Northwest Territories
D) Jurassic and Cretaceous deformations in the fold and thrust belt of the Canadian Rockies in

Question 33

Folded, fine grained turbidites that occur high in the Himalayas were originally deposited as sediments .

A) in a massive, Late Paleozoic syncline north of the Tibetan Plateau
B) in the accretionary wedge along the southern edge of Asia
C) along the shallow shoreline and continental shelf north of India
D) on the deep ocean abyssal plain south of India

Question 34

The oldest rocks are about and found in .

A) 1.6 b.y.; compressional mountain belts on continental margins
B) 3 b.y.; continental shield areas, deep within continents
C) < 5000 years; Ireland and Israel
D) 1.7- 1.9 b.y.; island arcs within the western Pacific

Question 35

Which mountain belt did not have a stage of continent- continent collision as it formed?

A) Himalayas
B) Urals
C) Appalachians
D) Andes

Question 36

As an inactive mountain belt ages, what happens to the adjacent crustal areas?

A) They uplift along with the mountains.
B) They subside in response to the added load of sediments eroded off of the mountains.
C) They are subducted.
D) They slide into the sea along transform faults.

Question 37

The Western Canada Foreland Basin and the Appalachian Foreland Basin both formed .

A) in Paleozoic time from the break up of Pangaea
B) by passive marginal subsidence in the Early Precambrian
C) in response to crustal thickening and mountain building from terrane accretion
D) from broad regions of down- flowing cool mantle

Question 38

Mountain belts formed in several stages by the opening and closing of the Iapetus Ocean in the Paleozoic, include the .

A) NE edge of Indian Ocean
B) East African rift
C) Appalachians and Caledonians
D) European Alps

Question 39

Rugged elevations are due to crustal extension, related to underlying mantle heat or convective upwelling, in the .

A) European Alps
B) NE edge of Indian Ocean
C) East African rift
D) Appalachians and Caledonians

Question 40

Low elevation rounded mountains and hogbacks underlain by thrusts and folds in easily- eroded Mesozoic and Cenozoic strata are found in this part of the Rockies.

A) Front Ranges
B) Foothills
C) Western Ranges
D) Main Ranges

Question 41

Which statement comes closest to describing the isostatic compensation under convergent continental mountain belts?

A) The extra elevation of mountains is maintained by active elastic compression supplied by earthquake cycles and crustal convergence.
B) The extra elevation of mountains is maintained almost entirely by rising mantle plumes.
C) The extra elevation of mountains, like that of icebergs above the sea, is held up by the weight of the denser material that their lower portions displace.
D) The extra elevation of mountains is accounted for by the missing mass from adjacent eroded valleys and flanking lowland areas.

Question 42

On an Andean- type convergent margin, the continental block contains the .

A) rotated block faults
B) accretionary wedge and high pressure- low temperature metasediments and metavolcanics
C) batholiths, volcanic arc, and high temperature- moderate pressure metamorphics
D) deep ocean trench and batholiths

Question 43

The have crust about twice as thick as normal.

A) Himalayan Range and Tibetan Plateau in northern India and southwestern China
B) Coast Ranges of British Columbia
C) Basin and Range Province in Arizona and Nevada
D) Appalachians of eastern Canada

Question 44

Subduction ceases in a(n) _ type of convergent plate margin.

A) continent- continent
B) continent- ocean
C) ocean- ocean
D) accretionary

Question 45

Active volcanic arcs above a young oceanic plate are associated with a(n) margin.

A) continent- continent
B) divergent
C) continent- ocean
D) ocean- ocean

Question 46

During the Late Paleozoic (Devonian through Carboniferous), the tectonic and topographic configuration of the Appalachian region in eastern North America was most similar to the

A) Afar Rift
B) western California
C) Andes
D) Himalayas and Tibetan Plateau

Question 47

Thick thrust sheets of massive Proterozoic and Paleozoic carbonates from glaciated peaks with steep cliffs on all sides like Castle Mountain in western Alberta are found in this part of the Rockies.

A) Foothills
B) Western Ranges
C) Main Ranges
D) Front Ranges

Question 48

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) terrane
D) suture

Question 49

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

A) exclusively of granite batholiths and rhyolite welded tuffs
B) mainly of organic-rich, black shales and beach-type sandstones
C) mainly of basaltic lava flows and minor, coralline limestone
D) of folded, quartz sandstone and shallow water, marine limestone

Question 50

The term refers specifically to the collection of all geologic processes and tectonic events that are responsible for building mountain belts.

A) erogenesis
B) orthogneisses
C) orogenesis
D) rifting

Question 51

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) experience rapid erosion that thins the crust and causes the area to subside
D) have thicker, higher- density mantle rocks beneath them at shallow depths

Question 52

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

A) east coast of the Japanese Islands
B) west coast of South America
C) north flank of the East Pacific Rise
D) west coast of Africa

Question 53

A(n) convergent plate margin is associated with an accretionary wedge.

A) Aleutian
B) Andean
C) collisional
D) accretionary

Question 54

Subduction zones include all of the following except for .

A) volcanic arcs
B) deep ocean trenches
C) magma generation
D) suture zones

Question 55

The Humber Zone (Valley and Ridge Province in USA) of the Appalachian Mountains is characterized by .

A) crustal stretching as Africa and Eurasia migrated away from North America
B) composite cone volcanoes above a volcanic arc
C) deeply eroded, late Paleozoic, fault- block mountains and valleys
D) sedimentary strata folded in late Paleozoic time

Question 56

Well defined linear mountain ridges with southwesterly- dipping slopes, steep upturned bounding thrusts and intervening linear strike valleys are found in this part of the Rockies.

A) Western Ranges
B) Main Ranges
C) Front Ranges
D) Foothills

Question 57

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

A) western margin of North America
B) southern margins of India and Australia
C) western margin of the mid- Atlantic ridge
D) western margin of Africa

Question 58

The have crust about twice as thick as normal.

A) northern end of the Appalachian mountains on Cape Breton Island
B) Sierra Nevada mountains in California
C) Cypress Hills in Alberta
D) Himalayan Range and Tibetan Plateau in northern India and SW China

Question 59

Rift valleys with mafic volcanics are _ margins.

A) ocean- ocean
B) continent- ocean
C) extensional
D) continent- continent

Question 60

In general, which of the following statements about elevated, compressive orogens is true?

A) Crust was thickened by previous mountain building; as isostatic uplift and erosion proceed, the crust is gradually reduced in thickness.
B) Crust is sucked into the mantle by increased convection under mountain belts.
C) Crust was thinned by extensional faulting in the past; isostatic uplift and erosion cause the crustal root to gradually thicken.
D) Crust is flattened by increased atmospheric pressure over mountain belts.

Question 61

Mountainous relief is due to the rotation and sinking of lithospheric blocks in a tectonic setting.

A) convergent continent- ocean
B) extensional
C) convergent continent- ocean
D) convergent ocean- ocean

Question 62

A(n) convergent plate margin is associated with a volcanic island arc.

A) accretionary
B) collisional
C) Aleutian
D) Andean

Question 63

How much downwarping of the crust of the Canadian shield occurred during the maximum of the last ice age?

A) 300- 400 m
B) 50- 100 m
C) <10 m
D) > several kilometres

Question 64

Obducted ophiolite and island arc sequences are part of a margin.

A) continent- ocean
B) ocean- ocean
C) divergent
D) continent- continent

Question 65

A is a ridge of steeply inclined, resistant strata exposed along the edges of an uplifted block of older rock.

A) shellback
B) hoodoo
C) monotreme
D) hogback

Question 66

What is the Meguma Zone in Nova Scotia (and similar rocks beneath the more southerly, continental shelf off the US eastern seaboard) thought to represent?

A) passive margin sequence from Gondwanaland as the Iapetus Ocean closed
B) Cretaceous and Tertiary shallow continental shelf deposits from North America's passive margin
C) passive margin sequence from Rodinia's rifted margin
D) Ordovician accretionary melange from the Taconic orogeny

Question 67

What is similar about the tectonic cause for the Western Canada Foreland Basin and the Appalachian Foreland Basin?

Question 68

Which would the Andean- type margin not have more of, in comparison to an Aleutian- type margin?

A) subaqueous mafic pyroclastics close to the volcanoes
B) felsic pyroclastics
C) deformed high pressure/low temperature accretionary wedge rocks
D) complicated crustal compressional structures

Question 69

Since the early Mesozoic, the has been passive tectonically.

A) western margin of North America
B) eastern margin of North America
C) western margin of South America
D) southern margin of Eurasia

Question 70

What are two broad ideas on the pace of evolution of continents?

Question 71

What kind of crust was the Avalon Terrane prior to its accretion to the Appalachians in the Acadian Orogeny in the Silurian and Devonian?

A) supracrustal Iapetus seafloor sediments and Gondwanaland passive margin succession
B) ophiolite- Iapetus Ocean crustal sequence
C) island arc sequence
D) microcontinental fragment rifted off Rodinia or Gondwanaland

Question 72

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) Tightly folded, continental shelf strata were squeezed between North America and the convergent, Bering- Siberian subcontinent.
D) A massive subcontinent of old igneous and metamorphic rocks (similar to India) was accreted during late Proterozoic time.

Question 73

What ocean basin was destroyed and finally had its last sliver obducted to make the ophiolite between the Humber Zone and the Gander Terrane?

A) Fundy
B) Arctic
C) Iapetus
D) Atlantic

Question 74

What unique geologic event happened to the Canadian and American prairies during the Cretaceous?

Question 75

Under what terrane would you look to find the original rift zone tensional faults from the Proterozoic break up of Rodinia?

A) Humber Zone (Valley and Ridge Province in USA) of folded, sedimentary rocks on the eastern edge of the Appalachians
B) Avalonia block (Acadian phase)
C) Meguma Zone
D) Dunnage Zone (Taconic phase)

Question 76

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

A) rhyolitic pyroclastic materials and lavas
B) andesitic lavas and pyroclastic materials
C) basaltic lava flows
D) ophiolites

Question 77

Intensely folded, thinly bedded, Paleozoic shales and carbonates cause this part of the Canadian Rockies to appear the most jagged and rough due to the easily- eroded shale interbeds.

A) Front Ranges
B) Foothills
C) Western Ranges
D) Main Ranges

Question 78

Despite the repetitive nature of Wilson cycles, give three reasons or variables that make each mountain belt unique.

Question 79

Southern Africa has been has been slowly rising for million years above a super plume.

A) 1500
B) 100
C) 400
D) 1000