Deck 12: Plate Tectonics: The Framework for Modern Geology

Question 1

Which one of the following is an important fundamental assumption underlying the plate tectonic theory?

A)Earth's magnetic field originates in the outer core.
B)Earth's diameter has been essentially constant over time.
C)Radioactive decay slows down at the extreme pressures of the inner core.
D)Earth's ocean basins are very old and stable features.

Answer 1

B

Question 2

________ was never proposed as evidence supporting the existence of Pangaea.

A)Geometric fit between South America and Africa
B)Islands of Proterozoic rocks along the Mid-Atlantic Ridge
C)Late Paleozoic glacial features
D)The Glossopteris flora

Answer 2

B

Question 3

Following technologic advances in ocean mapping that came from the Cold War in the 1950s and 1960s the new data from the ocean basins led ________ to propose the first model for seafloor spreading.

A)Sir Edward Bullard
B)Harry Hess
C)Keith Runcorn
D)Alfred Wegener

Answer 3

B

Question 4

Linear, magnetic patterns associated with mid-ocean ridges are configured as ________.

A)concentric circles about a rising plume of hot, mantle magma
B)reversed magnetizations along the present day rift valleys and normal magnetizations along the adjacent ridge
C)normal and reversed magnetized stripes roughly parallel to the ridge
D)normal and reversed magnetized stripes roughly perpendicular to the ridge axis

Question 5

What does the plate reconstruction, with the Atlantic Ocean closed up, do to the apparent polar wandering paths for Eurasia and North America, and what can we infer from this?

A)It makes them coincide, demonstrating that the opening of the Atlantic was the cause for the divergence seen today.
B)It makes them overlap but they are still strangely curved, implying the poles have still shifted so continental drift doesn't solve anything.
C)It indicates that the poles drift counterclockwise with time, implying Earth used to revolve the other way.
D)It really indicates that, because opposite polarities attract, the curves became stuck together.

Question 6

Wegener's supercontinent that began to break up about 200 million years ago was named ________.

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

Question 7

What was the unexpected contribution of Keith Runcorn and his students to the continental drift controversy?

A)Apparent polar wander paths for rocks of various ages in Europe demonstrated that either the magnetic pole, or the continent's position, had wandered with time.
B)Discordance of the Earth and Moon's magnetic pole orientations proved that the poles of one or both had drifted with the lithosphere since they were formed.
C)Magnetic stripes on the seafloor demonstrated magnetic reversals and seafloor spreading.
D)Reversed magnetic north directions preserved in rocks demonstrated that the location of Earth's axis had changed markedly throughout time, implying periodic cataclysms that shifted the continents during pole reversals.

Question 8

________ first related the symmetrical magnetic patterns in seafloor basalts to seafloor spreading at a mid-ocean ridge.

A)Evans, Smith, and Novak
B)Morley, Vine, and Matthews
C)Rodgers, Gershwin, and Hammerstein
D)Wegener, Holmes, and Wilson

Question 9

New oceanic crust and lithosphere are formed at ________.

A)divergent boundaries by submarine eruptions and intrusions of felsic magma
B)convergent boundaries by submarine eruptions and intrusions of felsic magma
C)divergent boundaries by submarine eruptions and intrusions of mafic magma
D)convergent boundaries by submarine eruptions and intrusions of mafic magma

Question 10

________ discovered transform faults and first proposed that Earth's outer shell comprises several rigid plates.

A)J)Tuzo Wilson
B)Charles Darwin
C)James Hutton
D)Harry Hess

Question 11

The top of the asthenosphere is closest to the surface ________.

A)along a mid-ocean ridge
B)along the length of a deep mantle plume
C)along a transform fault
D)along a subduction zone

Question 12

What is the inclination of Earth's magnetic field as recorded in a recent lava flow on a volcano in northern Peru?

A)nearly horizontal and pointing north
B)nearly vertical and pointing north
C)nearly horizontal and pointing south
D)nearly vertical and pointing south

Question 13

How can you tell from the apparent polar wandering curves for Eurasia and North America, when they were last together and had just started to drift apart?

A)about 200 million years ago because, for times older than that, their curves remain parallel and about the same distance apart
B)just recently, when the curves came together
C)more than 500 million years ago, because the curves are separated then
D)about 300 million years ago, because the curves really bend before that

Question 14

The former, late Paleozoic super continent is known as ________.

A)Pandemonia
B)Pancakea
C)Pangaea
D)Panatopia

Question 15

What is the inclination of Earth's magnetic field as recorded in a recent lava flow near 59 degrees north in Yukon?

A)steeply inclined and pointing north
B)nearly vertical and pointing south
C)nearly horizontal and pointing north
D)nearly horizontal and pointing south

Question 16

In the early part of the 20th century, ________ argued forcefully for continental drift.

A)Karl Wagner
B)Peter Rommel
C)Alfred Wegener
D)Bill Kohl

Question 17

Where is the inclination of Earth's magnetic field the steepest?

A)at the north and south poles
B)at the equator
C)latitudes between 45 and 50 degrees
D)in the Bermuda triangle

Question 18

How does the polar wander curve for Eurasia confirm Wegener's hypothesis that the Carboniferous (300 million years ago)coal beds were originally deposited when that land mass was near the equator?

A)To restore the 300 million year paleopole to today's north magnetic pole pushes Eurasia about 40 degrees of latitude farther south than it is today.
B)To have that pole position, the 300 million year coal beds must have had a steep magnetic inclination.
C)This means that Eurasia used to sit in the middle of the north Pacific Ocean 300 million year ago where the climate is warmer.
D)300 million years ago, the equator and magnetic poles had switched positions, so Eurasia was tropical then.

Question 19

Where is the inclination of Earth's magnetic field horizontal?

A)at the equator
B)at the north and south poles
C)latitudes between 45 and 50 degrees
D)in the Bermuda triangle

Question 20

What do the data points signify on the apparent polar wandering curves for Eurasia and North America?

A)the apparent positions for the north magnetic pole at various times in the past, from paleomagnetic measurements on different rock sequences in Eurasia and North America
B)where the north magnetic pole appears to be located as viewed from various locations on different continents of the northern hemisphere today
C)where the north magnetic pole will be at various times in the future if North America keeps moving east and Eurasia keeps moving west
D)laboratory locations where Eurasian and North America rock samples were taken to be tested

Question 21

New oceanic crust and lithosphere are formed at ________.

A)divergent boundaries by submarine eruptions and intrusions of rhyolitic magma
B)convergent boundaries by submarine eruptions and intrusions of rhyolitic magma
C)divergent boundaries by submarine eruptions and intrusions of basaltic magma
D)convergent boundaries by submarine eruptions and intrusions of basaltic magma

Question 22

Plates are moving apart from one another with a ________ plate boundary.

A)divergent
B)transform
C)convergent
D)strike-slip

Question 23

Why were Wegener's continental drift ideas rejected by many contemporary and later scientists?

A)His drift mechanism seemed impossible on the basis of known physical processes.
B)Land bridges were proven to have aided in animal and plant migrations.
C)The ocean basins were well known to be geologically young, Mesozoic and Cenozoic features.
D)The gravitational attractions of the Sun and Moon were not strong enough to move the continents from the southern to the northern hemisphere.

Question 24

The west coast of South America is associated with a ________ plate boundary.

A)convergent
B)transform
C)divergent
D)strike-slip

Question 25

Where lithosphere is sinking into the mantle, it is a ________ plate boundary.

A)convergent
B)transform
C)divergent
D)strike-slip

Question 26

________ plate boundary is characterized by arcs of explosive composite cone volcanoes and deep-ocean trenches.

A)Convergent
B)Transform
C)Divergent
D)Subduction

Question 27

The lithospheric plates in modern plate tectonic theory differ significantly from Wegener's continental drift hypothesis in that ________.

A)they are significantly thinner
B)several of the largest plates include both continental and oceanic crust
C)it is the oceans that do all of the moving, not the continents
D)we now know that the plate motions are driven by massive magnetic reversals

Question 28

A typical rate of seafloor spreading in the Atlantic Ocean is ________.

A)2 kilometres per year
B)2 metres per year
C)20 metres per year
D)2 centimetres per year

Question 29

What is the tectonic environment for the volcanoes Kilimanjaro and Mt.Kenya?

A)continental margin volcanic arc
B)continental rift
C)within-plate hot spot type
D)mid-ocean ridge seamounts

Question 30

Pangaea was ________.

A)a large, ocean basin that opened in the Triassic and closed in the Paleocene
B)a large, Precambrian shield area in Africa and South America that broke apart late in the Proterozoic Eon
C)a huge mountain range formed when Africa pushed northward into Europe in Eocene time
D)a super continent that formed in the late Paleozoic and broke apart in Triassic time

Question 31

The volcanoes and deep valleys of east Africa are related to a ________.

A)continental rift along which parts of the African continent are beginning to slowly separate
B)fault allowing Arabia to slip westward past east Africa and penetrate into Turkey
C)transform fault aligned with the Red Sea carrying the Arabian and African blocks in opposite directions
D)continental collision zone between Africa and the Zagros Mountains along the southern margin of Eurasia

Question 32

Why is so much mafic magma erupted along mid-ocean ridges?

A)Basaltic mantle under the ridge is hot enough to completely melt if seawater is added.
B)Lowered pressures decrease the temperatures at which mafic magma can partially melt from massive, extensive, rising plumes of mantle peridotite.
C)The subducting, oceanic slab sinks so deep that eventually it melts, producing massive quantities of mafic magma.
D)The mantle beneath the ridges is enriched in thorium, uranium, and potassium, causing strong heating due to energy from radioactive decay.

Question 33

Pull-apart, rift zones are generally associated with a ________ plate boundary.

A)divergent
B)transform
C)convergent
D)subduction

Question 34

If the North Atlantic began to rift about 200 million years ago, initiating the break up of Pangaea, where are the Jurassic basalts from that initial rifting?

A)as outcrops and as basement to the continental shelves' sediment sequences along the eastern seaboard of North America and along the western coast of north Africa
B)There aren't any left; they all got recycled back into the mantle along subduction zones underneath western Europe and Brazil.
C)on the Mid-Atlantic Ridge under Iceland
D)subducted beneath the Bermuda triangle

Question 35

The ________ is (are)a logical evolutionary analog of the African Rift Valleys ten million years from now.

A)Ural Mountains
B)San Andreas fault
C)Peru-Chile trench
D)Red Sea

Question 36

The modern-day Red Sea is explained by plate tectonics theory because it is ________.

A)a tiny remnant of a once immense ocean that was closed as Africa moved into Asia
B)the site of a transform fault along which Arabia is moving away from Africa
C)a rift zone that may eventually open into a major ocean if Arabia and Africa continue to separate
D)a rare example of a two continent subduction zone where both the African and Arabian continental plates are both sinking under the Red Sea plate

Question 37

Approximately ________ major lithospheric plates exist today.

A)11
B)2
C)7
D)4

Question 38

The distance between Halifax and London UK ________ each year due to plate movements.

A)increases two metres
B)increases two centimetres
C)decreases two centimetres
D)decreases eight meters

Question 39

The largest mostly oceanic plate is the ________.

A)Atlantic
B)Antarctic
C)Pacific
D)Scotian

Question 40

The mid-Atlantic ridge is a ________ plate boundary.

A)divergent
B)transform
C)convergent
D)strike-slip

Question 41

Mount St.Helens and the other Cascade volcanoes from Mt.Shasta in northern California to Mt.Garibaldi in southwestern B.C.are ________.

A)young, active composite volcanoes built on a continental margin above a sinking slab of oceanic lithosphere
B)a row of young, active, shield volcanoes built as western North America moved over a hot spot deep in the mantle
C)old, deeply eroded composite cones built before the Pacific Ocean existed
D)old, deeply eroded, basaltic shield volcanoes built when western North America was over the present-day site of the Hawaiian hot spot

Question 42

A curved line of volcanic islands spaced about 80 kilometres apart along the edge of one plate where two oceanic plates meet is called a(n)________.

A)hot spot track
B)oceanic volcanic rift zone
C)volcanic island arc
D)subsided and failed continental rift

Question 43

What important physical and chemical process occurs to subducted seafloor as it reaches a depth of 100 kilometres depth in the upper mantle?

A)It experiences nearly a doubling in its density as the subducted basalt recrystallizes to peridotite.
B)The subducted seafloor entirely melts generating a line of explosive volcanoes.
C)Heat from the surrounding mantle drives off water and other volatiles from the slab, which escape upwards, lowering the melting point of the overlying asthenospheric mantle.
D)The cooling of the ocean crust from the cold, deep ocean water of the trenches causes the subducted crust to freeze the mantle, cracking and freezing it to generate the largest earthquakes.

Question 44

What do the Appalachians have in common tectonically with the Himalayas?

A)They are both active, convergent, continental-margin arc systems.
B)They both formed by continental rifting.
C)They both formed by continent-continent collision.
D)They are both unusual places where ocean crust overrode the continent.

Question 45

Deep-hypocentre earthquakes, those between 300 and 700 km below the surface, occur only in association with ________.

A)subduction zones
B)mid-ocean ridges
C)transform faults
D)hot spots

Question 46

________ plate boundaries are characterized by arcs of explosive composite cones and deep-ocean trenches.

A)Convergent
B)Transform
C)Divergent
D)Strike-slip

Question 47

Deep-oceanic trenches are most abundant around the rim of the ________ ocean basin.

A)Atlantic
B)Indian
C)Arctic
D)Pacific

Question 48

Deep ocean trenches are surficial evidence for ________.

A)rifting beneath a continental plate and the beginning of continental drift
B)sinking of oceanic lithosphere into the mantle at subduction zones
C)rising of hot asthenosphere from deep in the mantle
D)transform faulting between an oceanic plate and a continental plate

Question 49

From the list below, which contribution did J.Tuzo Wilson make to Plate Tectonic theory?

A)the existence of mid-ocean ridges and the correlation of magnetic stripes to seafloor spreading
B)the existence of fracture zones in the ocean crust, rigid lithospheric plates, and intraplate hot spots
C)that the largest earthquake zones were over dipping oceanic plates
D)the rifting of continents like Pangaea and Gondwanaland

Question 50

Cooler, older, oceanic lithosphere sinks into the mantle at ________.

A)subduction zones along convergent plate boundaries
B)transform fault zones along divergent plate boundaries
C)rift zones along mid-ocean ridges
D)sites of long-lived, hot spot volcanism in the ocean basins

Question 51

The ________ is an example of an active, continent-continent collision.

A)Arabian Peninsula slamming into North Africa under the Red Sea
B)westward movement of the South American plate over the Nazca plate
C)northern movement of Haida Gwaii toward the Aleutian Trench
D)northward movement of India under Eurasia

Question 52

This plate boundary has the least amount of volcanism.

A)transform
B)convergent
C)divergent
D)subduction

Question 53

Deep-hypocentre earthquakes are associated with ________ plate boundaries.

A)divergent
B)convergent
C)transform
D)lateral

Question 54

The ________ were formed in the late Paleozoic when sediments in a marine basin were squeezed and crumpled between the converging continents of Europe and Asia.

A)Alps in Europe
B)northern Canadian Rockies
C)Andes in South America
D)Urals in Russia

Question 55

Most transform faults are located ________.

A)along the crests of mountain ranges like the Alpine fault in New Zealand
B)at ridge-ridge-ridge triple junctions
C)in the ocean basins connecting offsets along the oceanic ridge system
D)within continents at old continental sutures or along continental margins

Question 56

The chaotic accumulation of deformed oceanic sediments, and scraps of ocean crust found plastered onto a convergent continental margins, like that where the Cocos plate subducts beneath western Mexico, is called ________.

A)an accretionary wedge
B)a continental margin arc
C)the scrapie
D)a wedgie

Question 57

The Aleutian Islands occur at ________.

A)an ocean-ocean convergent boundary on a volcanic arc above a northward-subducting Pacific plate
B)a transform boundary where North America has moved towards Alaska
C)a divergent boundary where shield volcanoes are forming
D)a convergent, continental margin with uplifted fault blocks, much like those of the Basin and Range Province

Question 58

A transform plate boundary is characterized by ________.

A)composite volcanoes on the edge of a plate and shield volcanoes on the adjacent plate
B)two, converging, oceanic plates meeting head-on and piling up into a mid-ocean ridge
C)a divergent boundary where the continental plate changes to an oceanic plate
D)a deep, vertical strike-slip fault along which two plates slide past one another in opposite directions

Question 59

Plates are sliding past one another horizontally along a ________ plate boundary.

A)transform
B)convergent
C)divergent
D)subduction

Question 60

________ plate boundaries have the largest magnitude earthquakes.

A)Divergent and transform
B)Transform and convergent
C)Divergent and convergent
D)All plate boundaries have large magnitude earthquakes.

Question 61

The magnetic orientation and age of different regions of the seafloor is inferred from the total field intensity using towed magnetometers.

Question 62

In detail, there is no geologic evidence that mid-ocean ridges spread at uniform rates or even symmetrically.

Question 63

Which of the following most accurately describes the volcanoes of the Hawaiian Islands?

A)shield volcanoes fed by a long-lived hot spot below the Pacific plate
B)composite volcanoes associated with subduction and a convergent plate boundary
C)shield volcanoes associated with a mid-Pacific ridge and spreading centre
D)composite volcanoes associated with a mid-Pacific transform fault

Question 64

Which of the following energy sources is thought to directly drive the lateral motions of Earth's lithospheric plates?

A)tidal gravitational attractive forces of the Sun and Moon
B)electric and magnetic fields generated in and radiating from the inner core
C)export of heat from deep in the mantle to the top of the asthenosphere and descending cold material in a solid state convective flow
D)rotational spinning of the Earth, with the plates dragging behind

Question 65

Early results of the Deep Sea Drilling Program clearly justified the conclusion that ________.

A)the oceans have not always contained most of Earth's water
B)the ocean basins are relatively young; most ocean basin rocks and sediments are Cretaceous or younger in age
C)proterozoic rocks are found only as seamounts in the deepest parts of the ocean basins
D)the youngest sediments were deposited directly on the oldest seafloor basalts

Question 66

Early results of the Deep Sea Drilling Project clearly justified the conclusion that ________.

A)the oceans have not always contained most of Earth's water
B)the ocean basins are geologically young (C)Proterozoic rocks are found only as seamounts in the deepest parts of the ocean basins
D)the youngest sediments were deposited directly on the oldest seafloor basalts

Question 67

What span of seafloor motion is recorded by the hot spot track of the Hawaii-Emperor seamount chain?

A)0-65 million years
B)0-5 million years
C)0-27 million years
D)65-180 million years

Question 68

All of the following are evidence supporting the theory of plate tectonics except for ________.

A)changes in the Moon's orbit due to shifting plates
B)ocean floor drilling
C)hot spots
D)measurements of plate motions

Question 69

During various times in the geologic past, the polarity of Earth's magnetic field has been reversed.

Question 70

In the nomenclature of J.Tuzo Wilson, a very long-lived magma source rising from deep in the mantle is called a(n)________.

A)hot spot
B)old flame
C)basalt fount
D)melt welt

Question 71

Wegener's continental drift hypothesis was unanimously accepted by the international scientific community when he proposed it.

Question 72

What is the cause of the magmas currently erupting in the Hawaiian Islands?

A)shallow decompression melting of a fixed mantle plume, with magmas rising through the NW-moving Pacific plate
B)flux-melting associated with subduction and a convergence between two sub-plates in the Pacific basin
C)shallow decompression melting along a mid-Pacific ridge, spreading NE-SW
D)shear melting associated with a mid-Pacific transform fault

Question 73

The "big bend" in the Hawaii-Emperor seamount chain occurred at about 45 million years ago.What is the most likely explanation for this change in the orientation of the hot spot track across the Pacific plate?

A)From Cretaceous through 45 million years (Eocene), the Pacific seafloor used to move northwards as it subducted down a trench near the present Aleutians.Since then the Kurile-Kamchatka trench began subducting and the Pacific plate began moving NW instead.
B)The hot spot abruptly changed its direction.It used to move straight south, and since 45 million years ago it has been moving SE through the upper mantle.
C)They are two unrelated hot spot tracks that intersect.Originally there was an Emperor hot spot, then it died while the Hawaiian hot spot started up and moved in a new direction.
D)The Devil put this line of volcanoes here to confuse us and subvert us from the true path.Everyone knows Earth isn't really that old.

Question 74

What kind of geologic studies were the primary focus of the Glomar Challenger and JOIDES Resolution's international investigations?

A)conducting swath multi-beam bathymentry and other underway geophysical surveys to map the ocean basins
B)drilling the seafloor sediments and underlying ocean crust to determine the history and development of different oceanic regions
C)satellite mapping of the sea surface and spectroscopic analysis of surface currents for global current circulation and geochemistry
D)resource mapping on the continental shelves of Canada and other contributing member nations

Question 75

Which of the following is not part of the accepted driving mechanism of plate tectonic motions?

A)All of the heat for the mantle convection comes from small amounts of radioactive elements in the inner core.
B)The Earth's unequal distribution of internal heat is what drives the mantle convection and provides the heat engine.
C)Oceanic plates descend and constitute the downward-moving portion of Earth's internal convective flow.
D)Solid state convective flow in the rocky mantle, warm regions rising and cold regions sinking, is the basic driving force for plate motions.

Question 76

Anywhere in the world, ________ most effectively outline the edges of the lithospheric plates.

A)lines of active composite volcanoes
B)margins of the continental shelves
C)the locations of deep mantle hot spots
D)lines of earthquake epicentres

Question 77

Evidence for the supercontinent Pangaea includes fit of continents, matching fossils and mountain chains separated by ocean basins, and ancient glaciated rocks in the southern hemisphere.

Question 78

Deep-hypocentre earthquakes are associated with ________ plate boundaries.

A)divergent
B)convergent (subducting)
C)transform
D)strike-slip

Question 79

What is the most likely explanation for why there are no islands, only deep seamounts and guyots NW of Kauai towards Midway?

A)The seafloor farther from the current hot spot has aged and cooled off, so the volcanoes eroded and sank below sea level.
B)The hot spot was less vigorous from 27 to 65 million years than subsequently.
C)The Pacific plate moved much faster during the period in question and there wasn't time to build tall volcanoes over the Hawaiian hot spot.
D)The intervening seafloor is thinner so it sat higher and eroded off all the volcanoes.

Question 80

The magnetic inclination of a lava flow that originally cooled near the equator is shallow.