Chapter 2: Plate Tectonics: The Unifying Theory

Question 1

continental drift

Answer 1

The large-scale motion of continents across Earth’s surface driven by plate tectonics.

Question 2

geodesy

Answer 2

The ancient science of measuring the shape of the Earth and locating points on its surface.

Question 3

island arc

Answer 3

A linear or arc-shaped chain of volcanic islands formed on the seafloor at a convergent plate boundary. The islands are formed in the overriding plate from rising melt derived from fluid-induced melting of the mantle wedge above the downgoing lithospheric slab.

Question 4

isochron

Answer 4

A contour that connects rocks of equal age on the world’s ocean floors as determined by magnetic reversal data and fossils from deep-sea drilling.

Question 5

magnetic anomaly

Answer 5

A pattern of long, narrow bands of high and low magnetic fields on the seafloor that are parallel to and almost perfectly symmetrical with respect to the crest of a mid-ocean ridge.

Question 6

magnetic time scale

Answer 6

The detailed history of Earth’s magnetic-field reversals going back into geologic time, as determined by measuring the thermoremanent magnetization of rock samples.

Question 7

Pangaea

Answer 7

A supercontinent that coalesced in the latest Paleozoic era and comprised all present continents, then began to break up in the Mesozoic era.

Question 8

plate tectonics

Answer 8

The theory proposing that the lithosphere is broken into about a dozen large plates that move over Earth’s surface.(From the Greek tekton, meaning “builder.”)

Question 9

relative plate velocity

Answer 9

The velocity at which one plate moves relative to another plate

Question 10

Rodinia

Answer 10

A supercontinent older than Pangaea that formed about 1.1 billion years ago and began to break up about 750 million years ago.

Question 11

seafloor spreading

Answer 11

The mechanism by which new oceanic crust is formed at a spreading center on the crest of a mid-ocean ridge. As two plates move apart, magma wells up into the rift between them to form new crust, which spreads laterally away from the rift and is replaced continually by newer crust

Question 12

spreading center

Answer 12

A divergent boundary, marked by a rift at the crest of a mid-ocean ridge, where new oceanic crust is formed by seafloor spreading.

Question 13

subduction

Answer 13

The sinking of an oceanic plate (lithosphere) beneath an overriding oceanic or continental plate at a convergent plate boundary.

Question 14

transform fault

Answer 14

A plate margin at which the plates slide past each other and lithosphere is neither created nor destroyed. Relative displacement occurs along the fault as horizontal slip between the adjacent plates.

Question 15

convergent boundary

Answer 15

A boundary between lithospheric plates where the plates move toward each other and one plate is recycled into the mantle (Compare divergent boundary; transform fault)

Question 16

divergent boundary

Answer 16

A boundary between lithospheric plates where two plates move apart and new lithosphere is created (Compare convergent boundary; transform fault)

Question 17

mid-ocean ridge

Answer 17

An undersea mountain chain at a divergent boundary, characterized by earthquakes, volcanism, and rifting, all caused by the tensional forces of mantle convection that are pulling the two plates apart

Question 18

mantle plume

Answer 18

A narrow, cylindrical jet of hot, solid material rising from deep within the mantle, thought to be responsible for intraplate volcanism.

Question 19

Evidence for a supercontinent

Answer 19

• Fit of the continents
• Fossil evidence
• Evidence from rocks
• Paleoclimatic evidence

Question 20

Curie Point

Answer 20

580 degrees C. When iron grains in lava cool below this temperature, they become magnetized in the direction of the earth’s existing magnetic field

Question 21

Henry Hess

Answer 21

Proposed the hypothesis of seafloor spreading

Question 22

Number and names of the major plates

Answer 22

13: 7 largest are South American, North American, Pacific, Australian, Antarctic, Eurasian, African; remaining 6 are Indian, Arabian, Philippine, Nazca, Cocos, Caribbean (Juan de Fuca is a smaller plate off west coast of US/Canada)

Question 23

Rate that new oceanic crust is being generated

Answer 23

5 cm (2 in) per year

Question 24

Accretionary wedge

Answer 24

An accumulation of sediments and scraps of oceanic crust that are plastered to the leading edge of a contintental block

Question 25

backarc basin

Answer 25

a relatively small marginal sea

Question 26

terranes

Answer 26

Accreted crustal blocks (composes all of Alaska and western coastline of Canada and US.

Question 27

J Tuzo Wilson

Answer 27

First described transform faults

Question 28

Active zone

Answer 28

Between 2 separate ridge systems actively producing oceanic crust. In the active zone, the adjacent plate slabs grind past each other.

Question 29

Inactive zone

Answer 29

Outside the boundaries defined by the parallel ridge crests. At this point, beyond the ridges, the plate segments move in the same direction.

Question 30

hot spot

Answer 30

A region of intense, localized volcanism found far from a plate boundary; hypothesized to be the surface expression of a mantle plume

Question 31

Vine and Mathews

Answer 31

Associated magnetic reversals with seafloor spreading

Question 32

Ridge push

Answer 32

Tectonic force that moves earth’s plates: Gravity-driven force as new lithosphere slides down the flanks of oceanic ridge

Question 33

Slab suction

Answer 33

Tectonic force that moves earth’s plates: Induced mantle circulation that pulls the subducting and overriding plates towards the trench

Question 34

Slab pull

Answer 34

Tectonic force that moves earth’s plates: Gravity-driven, weight of subducting slab pulling the trailing lithosphere after it (primary force of plate motions)