Continental Drift and Plate Tectonics

Question 1

• (tekto = to build) are those that deform Earth’s crust to create major structural features, such as mountains, continents, and ocean basins.

Answer 1

Tectonic processes

Question 2

Wegener suggested that a single supercontinent named * consists all Earth’s landmasses once

Answer 2

Pangaea (“all lands”)

Question 3

According to the plate tectonics model, the crust and

the uppermost part of the mantle constitute Earth’s strong outer layer, the *

Answer 3

lithosphere (lithos = stone).

Question 4

Oceanic crust is composed of * and rich in dense iron and magnesium, whereas continental crust is composed largely of less dense * rocks.

Answer 4

basalt, granitic (mafic)

Question 5

The * is a hotter, weaker region in the mantle that lies below the lithosphere

Answer 5

asthenosphere (asthenos = weak)

Question 6

Although these rocks in asthenosphere are solid, they are quite *and respond to forces acting on them by exhibiting a slow * . By contrast, the comparatively cool and strong lithosphere tends to respond to forces acting on it by * . These differences result in Earth’s rigid outer shell being effectively detached from the underlying asthenosphere, which allows it to move independently of the layers below

Answer 6

ductile, fluid-like flow

bending or breaking

Question 7

where two plates move
apart, resulting in upwelling and partial melting of
hot material from the mantle to create new seafloor

Answer 7

Divergent plate boundaries

Question 8

where two plates move together, resulting either in oceanic lithosphere descending beneath an overriding plate, eventually to be reabsorbed into the mantle, or possibly in the collision of two continental blocks to createa mountain belt

Answer 8

Convergent plate boundaries

Question 9

where two plates grind past each other without the production or destruction of lithosphere

Answer 9

Transform plate boundaries

Question 10

Most divergent plate boundaries (di = apart, vergere =
to move) are located along the crests of * and can be thought of as constructive plate margins because this is where new ocean floor is generated
Two adjacent plates move away from each other,
producing long, narrow fractures in the ocean crust. As
a result, hot molten rock from the mantle below migrates upward to fill the voids left as the crust is being ripped apart.

Answer 10

oceanic ridges

Question 11

Divergent plate boundaries are also called *

Answer 11

spreading centers.

Question 12

• are elevated areas of the seafloor characterized by high heat flow and volcanism.
  The * is the longest
  topographic feature on Earth’s surface, exceeding
  70,000 kilometers (43,000 miles) in length.

Answer 12

Oceanic ridges, global oceanic ridge system

Question 13

any of several vast submarine regions that collectively cover nearly three-quarters of Earth’s surface. This includes the continental shelf, abyssal plain, mid-ocean ridge, etc.

Answer 13

Ocean basin

Question 14

Further, along the crest of some ridge segments is a deep Canyon-like structure called a *

Answer 14

rift valley

Question 15

The mechanism that operates along the oceanic ridge system to create new seafloor is appropriately called *

Answer 15

seafloor spreading.

Question 16

Spreading typically averages around *

Answer 16

5 centimeters (2
inches) per year

Question 17

As the tectonic forces continue to pull apart the crust,

the broken crustal fragments sink, generating an elongated depression called a

Answer 17

continental rift

Question 18

where two plates move toward each other and the leading edge of one is bent downward as it slides beneath the other.

Answer 18

convergent plate boundaries

Question 19

Convergent boundaries are also called * because they are sites where lithosphere is descending (being subducted) into the mantle.

Answer 19

subduction zones

Question 20

• occurs because the density of the descending lithospheric plate is greater than the density of the underlying asthenosphere

Answer 20

Subduction

Question 21

are long, linear depressions
in the seafloor that are generally located only a few hundred kilometers offshore of either a continent or a chain of volcanic islands such as the Aleutian chain

Answer 21

Deep-ocean trenches

Question 22

At a depth of roughly 100 kilometers (60 miles), the wedge of mantle rock is sufficiently hot that the introduction of water from the slab below leads to some melting called * . Being less dense than the surrounding mantle, this hot mobile material gradually rises toward the surface. Depending on the environment, these mantle-derived masses of molten rock may ascend through the crust and give rise to a volcanic eruption. However, much of this material never reaches the surface but solidifies at depth—a process that thickens the crust.

Answer 22

partial melting

Question 23

Where two oceanic slabs converge, one descends beneath the other, initiating volcanic activity by the same mechanism that operates at all subduction zones. The newly formed land, consisting of an arc-shaped chain of volcanic islands, is called a *

Answer 23

volcanic / island arc

Question 24

One landmass moves toward the margin of another. Because of subduction of the intervening seafloor, the buoyancy of continental material inhibits it from being subducted. The result is the formation of a new * composed of deformed sedimentary and metamorphic rocks that often contain slivers of oceanic lithosphere

Answer 24

mountain belt

Question 25

The subcontinent of * “rammed” into Asia, producing the * —the most spectacular mountain range on Earth

Answer 25

India, Himalayas

Question 26

Along a * , plates slide horizontally past one another without the production or destruction of lithosphere.

Answer 26

transform plate boundary, also called a transform fault

Question 27

Seafloor-spreading hypothesis predicted that the youngest oceanic crust would be found at the * , the site of seafloor production, and the oldest oceanic crust would be located * . Sediment thickness and age increases with * distance from the ridge

Answer 27

ridge crest, adjacent to the continents

increasing

Question 28

are areas where heat and/or rocks in the mantle are rising towards the surface. The surface manifestation of this activity is a *, an area of volcanism, high heat flow, and crustal uplifting that is a few hundred kilometers across.

Answer 28

Mantle plumes, hot spot

Question 29

Naturally occurring minerals are magnetic and are influenced by Earth’s magnetic field. One of the most common is the iron-rich mineral *, which is abundant in lava flows of * composition. The magnetite grains in molten lava are nonmagnetic. However, as the lava cools, these iron-rich grains become magnetized and align themselves in the direction of the existing magnetic lines of force.

Answer 29

magnetite, basaltic

Question 30

During a * , the magnetic north pole becomes the magnetic south pole and vice versa. When rocks exhibit the same magnetism as the present magnetic field, they are said to possess * polarity, whereas rocks exhibiting the opposite magnetism are said to have * polarity.

Answer 30

magnetic reversal

normal, reverse

Question 31

Earth has a * is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal.

Answer 31

magnetic field

Question 32

The flow of liquid iron in Earth’s core creates * , which in turn create the *

Answer 32

electric currents, magnetic field.