Geology Definitions Chapter 5

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continental drift

Back 1

A term, no longer used by geologists, that refers to the fact that continents are not stationary, but move across the Earth's surface.

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supercontinent

Back 2

a hypothetical protocontinent of the remote geologic past that riftedapart to form the continents of today.

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Pangaea

Back 3

supercontinent consisting of all of Earth's land masses.

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Ocean Ridge System

Back 4

a continuous underwater mountain range with parts found in every ocean of the world.

Front 5

Theory of Plate Tectonics

Back 5

lithosphere of the earth is divided into a small number of plates which float on and travel independently over the mantle

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Lithosphere

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the rigid outer part of the earth, consisting of the crust and upper mantle.

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Asthenosphere

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the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.

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lithospheric plate

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regions of Earth's crust and upper mantle that are fractured into plates that move across a deeper plasticine mantle.

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divergent plate boundary

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a linear feature that exists between two tectonic plates that are moving away from each other.

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rift valley

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a large unusually long depression with steep walls formed by the downward displacement of a block of the earth's surface between nearly parallel faults or fault systems.

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seafloor spreading

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the formation of new areas of oceanic crust, which occurs through the upwelling of magma at midocean ridges and its subsequent outward movement on either side.

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continental Rift

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the belt or zone of thecontinental lithosphere where the extensional deformation (rifting) is occurring

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convergent plate boundary

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an actively deforming region where two (or more) tectonic plates or fragments of the lithosphere move toward one another and collide.

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subduction zone

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when large pieces of material on thesubducting plate (such as island arcs) are pressed into the over-riding plate or when subhorizontal contraction occurs in the over-riding plate.

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deep ocean trench

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Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere

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partial melting

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only a portion of a solid ismelted.

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continental volcanic arc

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is formed at an activecontinental margin where two tectonic plates meet and a subduction zone develops.

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volcanic island arc

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they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench.

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transform fault boundary

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neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction.

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fracture zone

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a linear oceanic feature—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments.

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mantle plume

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a localized column of hot magma rising by convection in the mantle, believed to cause volcanic activity in hot spots,

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hot spot

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volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle..

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curie point

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temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism.

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paleomagnetism

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the branch of geophysics concerned with the magnetism in rocks that was induced by the earth's magnetic field at the time of their formation.

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magnetic reversal

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Changes in direction or orientation of the magnetic field of the Earth that have occurred from time to time.

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normal polarity

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is where the magnetic north points (roughly) towards the geographic north pole.

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magnetic time scale

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A list of dates of past geomagnetic polarity reversals

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magnetometer

Back 28

an instrument for measuring the intensity of a magnetic field,especially the earth's magnetic field.

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slab pull

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the portion of motion of a tectonic plate that can be accounted for by its subduction

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ridge push

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Ridge push or sliding plate force is a proposed mechanism for plate motion in plate tectonics. Because mid-ocean ridges lie at a higher elevation than the rest of the ocean floor, gravity causes theridge to push on the lithosphere that lies farther from the ridge.

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convection

Back 31

the transfer of heat by the circulation or movement of theheated parts of a liquid or gas.