Vocabulary For Ch 15 Of Essentials Of Geology

Front 1

asthenosphere

Back 1

A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is usually deformed

Front 2

continental drift

Back 2

A hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single supercontinent. Further beginning about 200 million years ago the supercontinent began breaking into smaller continents and drifted to their present positions

Front 3

continental volcanic arc

Back 3

Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. Examples include the Andes and the Cascades.

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convergent boundary

Back 4

A boundary in which two plates move together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle. It can also involve the collision of two continental plates to create a mountain system

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Curie point

Back 5

The temperature above which a material loses its magnetization

Front 6

deep-ocean trench

Back 6

An elongate depression in the seafloor produced by bending of oceanic crust during subduction

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divergent boundary

Back 7

A boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor.

Front 8

fossil magnetism (Paleomagnetism)

Back 8

The natural remnant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and the latitude of the rock at the time it became magnetized

Front 9

fracture zone

Back 9

Linear zone of irregular topography on the deep-ocean floor that follows transform faults and their inactive extensions

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hot spot

Back 10

A proposed concentration of heat in the mantle capable of introducing magma that in turn extrudes onto Earth's surface. The intraplate volcanism that produced the Hawaiian Islands is one example

Front 11

island arc (volcanic)

Back 11

A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another

Front 12

lithosphere

Back 12

The rigid outer layer of Earth, including the crust and upper mantle

Front 13

magnetic reversal

Back 13

A change in Earth's magnetic field from normal to reverse or vice versa

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magnetic time scale

Back 14

The detailed history of Earth's magnetic reversals developed by establishing the magnetic polarity of lava flows of known age

Front 15

magnetometer

Back 15

A sensitive instrument used to measure the intensity of Earth's magnetic field at various points

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mantle plume

Back 16

A mass of hotter than normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary.

Front 17

normal polarity

Back 17

A magnetic field the same as that which presently exists

Front 18

oceanic ridge system

Back 18

A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers. The rifts at the crests of these ridges represent divergent plate boundaries.

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Partial melting

Back 19

The process by which most igneous rocks melt. Because individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred a melt with a higher silica content results

Front 20

Pangaea

Back 20

The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses

Front 21

plate (lithospheric plate)

Back 21

A coherent unit of Earth's rigid outer layer that includes the crust and upper mantle

Front 22

plate tectonics

Back 22

The theory that proposes Earth's outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanos, mountains, and the crust itself

Front 23

reverse polarity

Back 23

A magnetic field opposite to that which presently exists

Front 24

ridge push

Back 24

A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.

Front 25

rift (rift valley)

Back 25

A region of Earth's crust along which divergence (separation) is taking place

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seafloor spreading

Back 26

The hypothesis first proposed in the late 1960s by Harry Hess that suggested that new oceanic crust is produced at the crests of mid-ocean ridges, whcih are the sites of divergence

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slab pull

Back 27

A mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along

Front 28

slab suction

Back 28

A mechanism that contributes to plate motion where the drag of a subducting slab on the adjacent mantle creates an induced mantle circulation that pulls both the subducting and overriding plates toward the trench

Front 29

subduction zone

Back 29

A long, narrow zone where one lithospheric plate descends beneath another

Front 30

transform fault boundary

Back 30

A boundary in which two plates slide past one another without creating or destroying lithosphere

Front 31

Subduction

Back 31

the process of thrusting oceanic lithosphere into the mantle along a convergent zone