Deck 12: Plate Tectonics and the Formation of the Earths Oceans

Question 1

The mechanisms for all of the following plate motions are somewhat understood EXCEPT:

A) motions of the continental lithosphere.
B) Pacific- style plate subduction.
C) lateral motion of oceanic plates.
D) Atlantic- style mid- ocean plate divergence.

Answer 1

A

Question 2

Which of the following statements about marine magnetic anomalies is NOT true?

A) The distance of a specific anomaly from a subduction zone is useful in determining plate velocity.
B) They are often symmetrical about mid- ocean ridges.
C) They represent alternating periods of time when the magnetic polarity of the Earth was reversed.
D) They are alternating bands of stronger and weaker magnetism in the rocks of the ocean floor.

Answer 2

A

Question 3

The breadth of an arc- trench gap at a subduction zone is determined by:

A) the angle at which the subducting plate descends.
B) the width of the volcanic arc.
C) the amount of material in the accretionary wedge.
D) the amount of material eroded from the adjacent continent and volcanic arc.

Answer 3

A

Question 4

The speed of tectonic plate movement varies from plate to plate in the range of:

A) 1 to 10 feet per year.
B) 1 to 10 millimeters per year.
C) 1 to 10 centimeters per year.
D) 1 to 10 inches per year.

Question 5

Which of the following is NOT a driving mechanism of plate tectonics?

A) Gravity- induced sliding.
B) Slab pull.
C) Upper- mantle convection.
D) Ridge push.

Question 6

The correct sequence of subduction- zone features from land seaward is:

A) continent, backarc basin, accretionary wedge, volcanic arc, forearc basin, trench.
B) continent, backarc basin, volcanic arc, forearc basin, accretionary wedge, trench.
C) continent, accretionary wedge, backarc basin, trench, forearc basin, trench, volcanic arc.
D) continent, forearc basin, accretionary wedge, volcanic arc, backarc basin, trench.

Question 7

All of the following are examples of rivers that follow the course of ancient failed rift EXCEPT:

A) North America's Mississippi River.
B) Yukon River in Alaska.
C) South America's Amazon River.
D) Africa's Niger River.

Question 8

Old, cold oceanic lithosphere is more dense than which of the following?

A) The underlying warm asthenosphere of the upper mantle.
B) Younger oceanic lithosphere.
C) The continental lithosphere.
D) All of the above.

Question 9

Unconsolidated sediments atop the oceanic lithosphere contain all of the following EXCEPT:

A) fine- grained, reddish brown clays.
B) calcareous microscopic marine organisms.
C) pillowed basaltic lavas.
D) siliceous microscopic marine organisms.

Question 10

A failed rift is:

A) any continental rifting in which a three- branched fracture has developed.
B) the two active arms of a three- branched fracture that forms after the initial stages of continental rifting.
C) the inactive arm of a three- branched fracture.
D) the juncture of a three- branched fracture in the initial stages of continental rifting.

Question 11

Which of the following mapping method studies layers beneath the ocean floor?

A) SEASAT.
B) Echo- sounding sonar.
C) Seismic profiling.
D) None of the above.

Question 12

Which of the following statements about suture zones is NOT true?

A) The suture zone may contain large masses of ophiolite rocks.
B) When the forward edges of two continental plates converge, neither subducts.
C) Thickening of the continental crust occurs because one plate is thrust slightly beneath the other.
D) Suture zones are likely zones of future rifting.

Question 13

A me´lange is a:

A) composite metamorphic rock formation formed at continental collision zones.
B) metamorphosed sequence of rocks that formerly constituted a vertical column of oceanic lithosphere.
C) sequence of rocks produced by subduction- zone volcanism.
D) composite mixture of rock and sediment pressed against the inner wall of a subduction trench.

Question 14

Guyots are flat primarily because:

A) they are volcanic and have been covered by horizontal basalt flows.
B) they are covered by horizontal layers of sediment.
C) they have been planed off by weathering, stream erosion, and ocean waves.
D) they are the tops of submarine horsts, fault blocks that have been raised from the sea floor.

Question 15

An ophiolite suite is:

A) the sequence of rocks that makes up a subduction zone.
B) the sequence of rocks that makes up oceanic lithosphere.
C) the sequence of rocks that makes up the mid- ocean ridge.
D) the sequence of rocks that makes up a continental suture zone.

Question 16

The Hawai'ian Islands and the Emperor Seamount chain were formed by:

A) a hot spot that migrates to the northwest beneath the Pacific plate.
B) the Pacific plate, which is moving in a northwest direction over a stationary hot spot.
C) the Pacific plate, which is moving in a southeast direction over a stationary hot spot.
D) a hot spot that migrates to the southeast beneath the Pacific plate.

Question 17

Which of the following methods uses gravity anomalies to create maps of the ocean floor?

A) SEASAT.
B) Seismic profiling.
C) Deep Sea Drilling Project.
D) Echo- sounding sonar.

Question 18

Which of the following are conclusions that can be drawn about a plate's speed and direction of movement from a seamount chain?

A) The youngest seamount will be the farthest from the hot spot, and an arrow from the seamount to the hot spot indicates the direction of plate movement.
B) The oldest seamount will be the farthest from the hot spot, and an arrow from the seamount to the hot spot indicates the direction of plate movement.
C) The oldest seamount will be the farthest from the hot spot, and an arrow from the hot spot to the seamount indicates the direction of plate movement.
D) The youngest seamount will be the farthest from the hot spot, and an arrow from the hot spot to the seamount indicates the direction of plate movement.

Question 19

Me´langes typically contain all of the following EXCEPT:

A) siliceous and carbonate oozes.
B) basalts and serpentinized gabbros and peridotites.
C) submarine granites and andesites.
D) clastic sediments derived from the adjacent continent.

Question 20

Hot spots can be used as "fixed" reference points for determining plate speed and direction because:

A) they move more slowly than the overlying plates.
B) they do not move at all.
C) they move in an opposite direction to the moving plate.
D) they move more rapidly than the overlying plates.

Question 21

List the factors that drive plate tectonic. .

Question 22

The correct sequence of an ophiolite suite, from top to bottom, is:

A) unconsolidated sediments, basalt layer, gabbro, peridotite.
B) unconsolidated sediments, basalt layer, peridotite, gabbro.
C) unconsolidated sediments, gabbro, peridotite, basalt layer.
D) basalt layer, unconsolidated sediments, gabbro, peridotite.

Question 23

All of the following are examples of a particular stage of rifting EXCEPT:

A) the Great Rift valley of East Africa, which may be a failed arm of a three- branched rift.
B) the Red Sea, which is an active arm of continuing divergence.
C) the Rio Grande region of Colorado and New Mexico, which is an area of initial crustal stretching and thinning.
D) the northeast coast of the United States, which shows evidence of future rifting.

Question 24

Which of the following methods of studying the sea floor incorporates energy waves generated by small targeted explosions?

A) Laser imaging.
B) Echo- sounding sonar.
C) Seismic profiling.
D) Microwave reflection.

Question 25

All of the following are useful in determining the plate velocity EXCEPT:

A) changes in the time it takes ships to cross the ocean.
B) the distance of a marine magnetic anomaly from a mid- ocean ridge.
C) changes in the time it takes for a laser beam to return from a satellite.
D) radiometric dating of seamount chains.

Question 26

The chimney- like structures around the "black smokers" are encrusted with:

A) mineral precipitates rich in metals.
B) basaltic flows.
C) giant clams and exotic tubeworms.
D) copper, iron, zinc, and silver deposits.

Question 27

What is a suture zone? Describe the geologic materials that might be included in the folded and faulted mountains that result from continental collisions.

Question 28

How do oceanic hot spots and continental hot spots differ?

Question 29

What are some of the basic assumptions of the theory of plate tectonics?

Question 30

At divergent zones, earthquakes commonly occur:

A) between offset segments, where segments move in opposite directions.
B) beyond the ridge segments, where segments move in the same direction.
C) at the ridge itself, where magma rises to the surface.
D) at the ridge itself, where normal faulting occurs.

Question 31

All of the following are evidence of forces that drive plate movement EXCEPT:

A) oceanic lithosphere moves laterally away from elevated mid- ocean ridges.
B) tears and fissures occur in axial rift valleys.
C) plates that are undergoing subduction are moving faster than plates that lack subducting margins.
D) magma rising between diverging oceanic plates causes folding in the newly formed lithosphere.

Question 32

Rifting sometimes stops after an initial period of faulting and volcanism:

A) because the asthenosphere convection current ceases.
B) but it is not known why such rifting ceases.
C) because the position of other plates stops further movement.
D) because the asthenosphere convection current is too weak to move the plates further.

Question 33

All of the following statements describe the effects of plate tectonics on Earth Systems EXCEPT:

A) rifting and associated volcanic activity may have contributed to extinctions.
B) gas emissions from subduction- zone volcanoes may alter the Earth's climate.
C) pieces of old subducted plates are recycled in the deep mantle.
D) convergent zones may have been the site where complex organic molecules formed.

Question 34

The LAGEOS satellite is used to:

A) determine plate movement by staying in orbit over the plate that is being measured.
B) determine directional plate movements as the satellite changes latitudinal directions.
C) determine the rate of plate movement by providing a fixed reference point.
D) determine plate velocity by changing speeds until there is a fixed mathematical ratio.

Question 35

In which stage of the rifting process are plate edges considered to be passive continental margins?

A) After rifting has been completed.
B) As basalts begin to fill the rift to form new ocean crust.
C) In the initial stages of continental rifting.
D) When seawater from an adjacent ocean inundates a young rift.

Question 36

What is the process of backarc spreading?

Question 37

The process of backarc spreading occurs as a result of:

A) extensive sedimentation into the backarc basin from both the continent and the volcanic arc.
B) the rifting of the overriding plate and the extrusion of basaltic magma.
C) movement of the continental plate away from the subduction zone.
D) seaward migration of the volcanic arc as it is pulled toward the trench by the subducting plate.

Question 38

List geographic examples of each stage of rifting, from the initial thinning of the crust to the closing of an ocean.