Chapter 02 Vocab

Question 1

absolute plate velocity

Answer 1

The movement of a plate relative to a fixed point in the mantle.

Question 2

abyssal plain

Answer 2

A broad, relatively flat region of the ocean that lies at least 4.5 km below sea level.

Question 3

accretionary prism

Answer 3

A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate at a convergent plate margin.

Question 4

active margin

Answer 4

A continental margin that coincides with a plate boundary.

Question 5

apparent polar-wander path

Answer 5

A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly fixed.

Question 6

asthenosphere

Answer 6

The layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.

Question 7

bathymetry

Answer 7

Variation in depth.

Question 8

black smoke

Answer 8

The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools.

Question 9

collision

Answer 9

The process of two buoyant pieces of lithosphere converging and squashing together.

Question 10

continental drift

Answer 10

The idea that continents have moved and are still moving slowly across the Earth’s surface.

Question 11

continental rift

Answer 11

A linear belt along which continental lithosphere stretches and pulls apart.

Question 12

continental shelf

Answer 12

A broad, shallowly submerged fringe of a continent; ocean-water depth over the continental shelf is generally less than 200 meters; the widest continental shelves occur over passive margins.

Question 13

convergent boundary

Answer 13

A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct.

Question 14

divergent boundary

Answer 14

A boundary at which two lithosphere plates move apart from each other; they are marked by mid-ocean ridges.

Question 15

fracture zone

Answer 15

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.

Question 16

global positioning system (GPS)

Answer 16

A satellite system people can use to measure rates of movement of the Earth’s crust relative to one another, or simply to locate their position on the Earth’s surface.

Question 17

hot spot

Answer 17

A location at the base of the lithosphere, at the top of a mantle plume, where temperatures can cause melting.

Question 18

hot-spot track

Answer 18

A chain of now-dead volcanoes transported off the hot spot by the movement of a lithosphere plate.

Question 19

lithosphere

Answer 19

The relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle.

Question 20

magnetic anomaly

Answer 20

The difference between the expected strength of the Earth’s magnetic field at a certain location and the actual measured strength of the field at that location.

Question 21

magnetic declination

Answer 21

The angle between the direction a compass needle points at a given location and the direction of true north.

Question 22

magnetic dipole

Answer 22

An imaginary vector that points from the north magnetic pole to the south magnetic pole of a magnetic field.

Question 23

magnetic inclination

Answer 23

The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth’s surface.

Question 24

magnetic pole

Answer 24

The ends of a magnetic dipole; all magnetic dipoles have a north pole and a south pole.

Question 25

magnetic-reversal chronology

Answer 25

The history of magnetic reversals through geologic time.

Question 26

magnetic reversal

Answer 26

The change of the Earth’s magnetic polarity; when a reversal occurs, the field flips from normal to reversed polarity, or vice versa.

Question 27

mantle plume

Answer 27

A column of very hot rock rising up through the mantle.

Question 28

mid-ocean ridge

Answer 28

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.

Question 29

paleomagnetism

Answer 29

The record of ancient magnetism preserved in rock.

Question 30

paleopole

Answer 30

The supposed position of the Earth’s magnetic pole in the past, with respect to a particular continent.

Question 31

Pangaea

Answer 31

A supercontinent that assembled at the end of the Paleozoic Era.

Question 32

passive margin

Answer 32

A continental margin that is not a plate boundary.

Question 33

plate boundary

Answer 33

The border between two adjacent litho sphere plates.

Question 34

plate tectonics

Answer 34

The theory that the outer layer of the Earth (the lithosphere) consists of separate plates that move with respect to one another.

Question 35

relative plate velocity

Answer 35

The movement of one litho sphere plate with respect to another.

Question 36

rifting

Answer 36

The process by which a continent stretches and splits along a belt; if it is successful, rifting separates a larger continent into two smaller continents separated by a divergent boundary.

Question 37

sea-floor spreading

Answer 37

The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.

Question 38

seamount

Answer 38

An isolated submarine mountain

Question 39

slab-pull force

Answer 39

The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin.

Question 40

spreading rate

Answer 40

The rate at which sea floor moves away from a mid-ocean ridge axis, as measured with respect to the sea floor on the opposite side of the axis.

Question 41

subduction

Answer 41

The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate.

Question 42

transform boundary

Answer 42

A boundary at which one litho sphere plate slips laterally past another.

Question 43

trench

Answer 43

A deep, elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary.

Question 44

triple junction

Answer 44

A point where three lithosphere plate boundaries intersect.

Question 45

volcanic arc

Answer 45

A curving chain of active volcanoes formed adjacent to a convergent plate boundary.

Question 46

Wadati-Benioff zone

Answer 46

A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary.