Chapter 04 Plate Techtonics

The rate of motion of a lithospheric plate with respect to a stationary hot spot is termed ____________. a. absolute plate velocity b. relative plate velocity

a. absolute plate velocity

Large, thick, nonvolcanic mountain belts, like the Himalayas, have features associated with ____________ plate boundaries. a. convergent b. divergent c. transform

a. convergent

The volcanoes of the Cascades Mountains are related to melting of rock associated with a ____________ plate boundary. a. convergent b. divergent c. transform

a. convergent

Under the theory of plate tectonics, the plates themselves are ____________. a. discrete pieces of lithosphere at the surface of the solid Earth that move with respect to one another b. composed only of continental rocks that plow through the weaker oceanic rocks c. very thick (approximately one-quarter of Earth's radius) d. discrete layers of lithosphere that are vertically stacked one atop the other

a. discrete pieces of lithosphere at the surface of the solid Earth that move with respect to one another

At transform plate boundaries ____________. a. earthquakes are common but volcanoes are absent b. volcanoes are common but earthquakes do not occur c. both earthquakes and volcanoes are common

a. earthquakes are common but volcanoes are absent

All portions of the mid-ocean ridge system have a well-defined axial trough (central rift). a. false b. true

a. false

The only igneous rocks produced at the mid-ocean ridges consist of basalt. a. false b. true

a. false

Hawaii is an example of ____________. a. hot-spot volcanism b. volcanic island arc c. transform margin d. mid-ocean ridge volcanism

a. hot-spot volcanism

At a divergent plate boundary (shown below), two opposed plates ____________. a. move away from one another b. move toward one another c. slide past one another

a. move away from one another

Continental coastlines that occur within the interior of a tectonic plate are called ____________. a. passive margins b. inert margins c. active margins d. internal margins

a. passive margins

Hot-spot tracks result from moving _____________. a. plates b. asthenosphere c. mantle plumes d. hot spots

a. plates

At a transform plate boundary (shown below), two opposed plates ____________. a. slide past one another b. move toward one another c. move away from one another

a. slide past one another

The primary difference between lithospheric and asthenospheric mantle that gives rise to numerous divergent patterns of physical behavior, is ____________. a. temperature (the lithosphere is cooler than the asthenosphere) b. physical state (the lithosphere is solid; the asthenosphere is liquid) c. chemical composition (the lithosphere is mafic; the asthenosphere is felsic) d. chemical composition (the lithosphere is felsic; the asthenosphere is mafic)

a. temperature (the lithosphere is cooler than the asthenosphere)

The number of lithospheric plates on the Earth has been variable through geologic time. Hundreds of millions of years ago, there were plates that no longer exist today. a. true b. false

a. true

As compared to a slowly spreading mid-ocean ridge, a rapidly spreading ridge is ____________. a. wider b. more silicic in lava composition c. narrower

a. wider

Hot spots can occur ____________. a. within either continental or oceanic plates b. only within continental plates c. only when the thickness of the crust is less than 10 km d. only within oceanic plates

a. within either continental or oceanic plates

Tectonic plates move at rates that are approximately ____________. a. 10 to 100 m/year b. 1 to 15 cm/year c. 1 to 5 cm every 1,000 years d. 1 to 15 m/year

b. 1 to 15 cm/year

The average thickness of continental lithosphere is about ____________. a. 60 km b. 150 km c. 30 km d. 10,000 km

b. 150 km

The Wadati-Benioff zone extends down within the mantle to a maximum depth of ____________. a. 990 km b. 670 km c. 30 km d. 150 km

b. 670 km

______________ is an example of a continental rift and the ______________ is/are the result of collision. a. The Basin and Range Province; mid-ocean ridge b. The Basin and Range Province; Himalayan Mountains c. A mid-ocean ridge; Himalayan Mountains d. The San Andreas Fault; Himalayan Mountains

b. The Basin and Range Province; Himalayan Mountains

A guyot is ____________. a. an extinct oceanic hot-spot volcano that has not yet subsided below sea level b. an extinct oceanic hot-spot volcano that has subsided below sea level c. any portion of the ocean floor that is topographically higher than surrounding sea floor d. synonymous with the term hot spot

b. an extinct oceanic hot-spot volcano that has subsided below sea level

A volcanic island arc forms when _______________. a. an oceanic plate subducts beneath continental lithosphere b. an oceanic plate subducts beneath another oceanic plate c. continental lithosphere subducts beneath an oceanic plate d. two oceanic plates collide

b. an oceanic plate subducts beneath another oceanic plate

When two bodies of continental lithosphere are pulled together at a convergent boundary, the result is ____________. a. subduction b. collision and mountain formation

b. collision and mountain formation

Deep oceanic trenches are features of ____________ plate boundaries. a. transform b. convergent c. divergent

b. convergent

The lithosphere of the Earth is generally thickest at and near ____________ plate boundaries. a. divergent b. convergent c. transform

b. convergent

Slab pull occurs because subducting slabs are ____________. a. hotter, and therefore more dense, than surrounding asthenosphere b. cooler, and therefore more dense, than surrounding asthenosphere c. cooler, and therefore less dense, than surrounding asthenosphere d. less mafic, and therefore less dense, than surrounding asthenosphere

b. cooler, and therefore more dense, than surrounding asthenosphere

Iceland is one of the few places in the world that is both above sea level and situated atop a ____________ plate boundary. a. convergent b. divergent c. transform

b. divergent

The lithosphere of the Earth is generally thinnest at and near ____________ plate boundaries. a. transform b. divergent c. convergent

b. divergent

Mid-ocean ridges are ____________. a. convergent plate boundaries b. divergent plate boundaries c. transform plate boundaries

b. divergent plate boundaries

All lithospheric plates are approximately the same size and contain a combination of oceanic and continental crust. a. true b. false

b. false

In a hot-spot volcanic island chain, such as the Hawaiian Islands, all islands possess active volcanoes simultaneously and therefore the risks of volcanic hazards are about the same for all islands. a. true b. false

b. false

Sliding motion along transform faults caused the segments of the mid-ocean ridges to become dislocated with respect to one another. a. true b. false

b. false

Virtually all of the sediment atop a downgoing plate becomes subducted into the mantle along with the plate. a. true b. false

b. false

Unlike the lithosphere, the asthenosphere ____________. a. has a density similar to the core b. is able to flow over long periods of time c. is relatively cool d. varies in thickness from place to place

b. is able to flow over long periods of time

At a convergent plate boundary (shown below), two opposed plates ____________. a. slide past one another b. move toward one another c. move away from one another

b. move toward one another

Broad, sediment-covered continental shelves are found along ____________. a. active margins b. passive margins

b. passive margins

Deformed (bent, stretched, or cracked) lithosphere occurs ____________. a. randomly over the surface of Earth b. primarily on the margins of tectonic plates c. primarily within the interiors of tectonic plates

b. primarily on the margins of tectonic plates

Summed over the entire surface of Earth, ____________. a. the rate of lithospheric production at ridges is greater than the rate of lithospheric consumption at subduction zones b. rates of lithospheric production and consumption are equal c. the rate of lithospheric consumption at subduction zones is greater than the rate of lithospheric production at ridges

b. rates of lithospheric production and consumption are equal

The mid-ocean ridges are elevated above the surrounding sea floor because ____________. a. the lithospheric plates are thickest at the ridges so they stand up taller b. ridge rocks are hot and therefore of relatively low density c. ridge rocks are mafic, whereas the ocean basin crust consists of ultramafic rock d. rising ocean currents leave a vacuum above the ridge

b. ridge rocks are hot and therefore of relatively low density

As lithosphere cools to the sides of a mid-ocean ridge, it begins to ____________. a. rise with respect to material located closer to the ridge axis b. sink with respect to material located closer to the ridge axis

b. sink with respect to material located closer to the ridge axis

According to the figure below, every plate boundary can be recognized by ____________. a. the presence of active volcanoes b. the presence of an earthquake belt c. a deep chasm that can be seen from space d. None of the above are correct.

b. the presence of an earthquake belt

The San Andreas Fault zone in southern California is an example of a ____________ plate boundary. a. convergent b. transform c. divergent

b. transform

Subducted slabs have never been detected below the Wadati-Benioff zone. a. false b. true

b. true

Within the terminology of plate tectonics, an active margin is ____________. a. anywhere on Earth where earthquakes are especially frequent b. synonymous with "subduction zone" c. a continental coastline that coincides with a plate boundary d. a 5-mile radius surrounding an active volcano

c. a continental coastline that coincides with a plate boundary

The youngest sea floor occurs ____________. a. along passive margins b. randomly over the entire ocean basin c. along mid-ocean ridges d. along active margins

c. along mid-ocean ridges

Most of the pushing force driving plate motion is produced ____________. a. at collision zones b. in the interiors of continental plates c. at mid-ocean ridges d. at subduction zones

c. at mid-ocean ridges

Most of the pulling force driving plate motion is produced ____________. a. in the interiors of continental plates b. at mid-ocean ridges c. at subduction zones d. at collision zones

c. at subduction zones

Subduction zones are ____________. a. divergent plate boundaries b. transform plate boundaries c. convergent plate boundaries

c. convergent plate boundaries

The theory of plate tectonics ____________. a. incorporates continental drift but not sea-floor spreading b. incorporates sea-floor spreading but not continental drift c. incorporates and explains both sea-floor spreading and continental drift d. does not incorporate sea-floor spreading or continental drift

c. incorporates and explains both sea-floor spreading and continental drift

At a subduction zone, the downgoing (subducting) plate ____________. a. may be composed or either oceanic or continental lithosphere b. is always composed of continental lithosphere c. is always composed of oceanic lithosphere

c. is always composed of oceanic lithosphere

Continental lithosphere ____________. a. contains no crustal material, consisting solely of lithified upper mantle b. is denser than oceanic lithosphere c. is thicker than oceanic lithosphere d. contains more mafic rocks than oceanic lithosphere

c. is thicker than oceanic lithosphere

The lithosphere of Earth can be bent and broken, but will not flow because it ____________. a. contains radioactive elements b. is too dense c. is too cool d. is too old

c. is too cool

At a subduction zone, the overriding plate ____________. a. is always composed of continental lithosphere b. is always composed of oceanic lithosphere c. may be composed of either oceanic or continental lithosphere

c. may be composed of either oceanic or continental lithosphere

Tectonic plates might consist of ____________. a. continental lithosphere only b. oceanic lithosphere only c. oceanic or continental lithosphere or a combination of both d. either oceanic or continental lithosphere, but not both

c. oceanic or continental lithosphere or a combination of both

A triple junction, like the one shown below, is a place on Earth's surface where ____________. a. three volcanoes form a tight, triangular cluster b. the boundaries of three lithospheric plates meet to form an elongate surface c. the boundaries of three lithospheric plates meet at a single point d. glacial ice, continental rocks, and the ocean can be found together

c. the boundaries of three lithospheric plates meet at a single point

Segments of the mid-ocean ridge system are offset. Between the offset segments we observe ____________. a. a second series of ridges, perpendicular to the main set b. deep ocean trenches c. transform faults d. None of the above are correct.

c. transform faults

Earthquakes are most frequent near coastlines that are termed ____________. a. geodesic margins b. passive margins c. aseismic margins d. active margins

d. active margins

Hot spots are caused by ____________. a. factors that remain completely unknown at this time b. unusually dense concentrations of radioactive isotopes at various points in the crust c. friction due to the lithosphere sliding atop the asthenosphere d. hot plumes of mantle material that rises up through cooler, denser surrounding rock

d. hot plumes of mantle material that rises up through cooler, denser surrounding rock

As compared to the density of the asthenosphere, the oceanic lithosphere is ____________. a. always more dense b. always less dense c. initially more dense at the age of formation, but eventually becomes less dense d. initially less dense at the age of formation, but eventually becomes more dense

d. initially less dense at the age of formation, but eventually becomes more dense

The thickness of oceanic lithosphere is ____________. a. greatest near the mid-ocean ridges and thins out away from the ridges b. uniformly 100 km c. greatest at the geographic poles and least near the equator d. least near the mid-ocean ridges and thickens away from the ridges

d. least near the mid-ocean ridges and thickens away from the ridges

The pulling forces that produce the most rapid plate velocities are concentrated at ____________. a. stable continental interiors b. mid-ocean ridges c. continental collision zones d. ocean trenches

d. ocean trenches

Oceanic lithosphere thickens away from the mid-ocean ridge primarily due to ____________. a. the addition of new crust due to sedimentation b. the addition of new crust due to hot-spot volcanism c. reasons that geologists cannot determine at present d. the addition of new lithospheric mantle as a result of cooling

d. the addition of new lithospheric mantle as a result of cooling

According to Archimedes' principle of buoyancy, an iceberg sinks until _____________. a. the total mass of the water displaced equals 80% of the mass of the iceberg b. about 60% of the iceberg is underwater c. the total mass of the iceberg is underwater d. the total mass of the water displaced equals the total mass of the whole iceberg

d. the total mass of the water displaced equals the total mass of the whole iceberg

The Wadati-Benioff zone is a belt of earthquakes found ____________. a. within an otherwise stable continental interior b. within an overriding plate at a subduction zone c. along mid-ocean ridges d. within a downgoing plate at a subduction zone

d. within a downgoing plate at a subduction zone