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CH.8 plate tectonics
definitions
| Term | Definition |
|---|---|
| asthenosphere | 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 easily deformed. |
| continental drift | a theory that originally proposed that the continents are rafted about. it has essentially been replaced by the plate tectonics theory. |
| continental rift | a linear zone along which continental lithosphere stretches and pulls apart. its creation may mark the beginning of new ocean basin. |
| continental volcanic arc | mountains formed in part of igneous activity associated with the subduction of oceanic lithosphere beneath a continent. |
| convergent boundary | a boundary in which two plates move together, causing one of the slabs of lithosphere to be consumed into the mantle as it descends beneath on an overriding plate. |
| curie point | the temperature above which a material loses its magnetization |
| deep-ocean trench | an elongated depression in the seafloor produced by bending of oceanic crust during subduction. |
| divergent boundary or spreading center | a region where the rigid plates are moving apart, typified by the mid-oceanic ridges. |
| fossil magnetism or paleomagnetism | 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 it became magnetized. |
| fracture zone | any break or rupture in rock along which no appreciable movement has taken place. |
| hot spot | a concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface. the intraplate volcanism that produced the hawaiian Islands is one example. |
| hot spot track | Chain of volcanic structures produced as a lithosperic plate moves over a mantle plume. |
| island arc | a chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occuring. |
| lithosphere | the rigid outer layer of earth, including the cr5ust and upper mantle. |
| lithospheric plate | a coherent unit of Earth's rigid outer layer that includes the crust and upper unit. |
| magnetic reversal | a change in Earth's magnetic field from normal to reverse or vice versa. |
| magnetic time scale | a scale that shows the age of magnetic reversals and is based on the polarity of lave flows of various ages. |
| magnetometer | a sensitive instrument used to measure the intensity of Earth's magnetic field at various points. |
| mantle plume | a mass of hotter-than-normal mantle material that ascends towar 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. |
| normal polarity | a magnetic field that is the same as that which exists at present. |
| oceanic ridge system | a continuous elevated zone on the floor of all the major ocean basins and varying in width from 500 to 5,00 kilometers (300-3,000 miles). the rifts at the crests of ridges represent divergent plate boundaries. |
| Pangea | The proposed supercontinent that 200 million years ago began to break apart and form the present land masses |
| partial melting | the process by which most igneous rocks melt. since 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, silica content results |
| plate tectonics | the theory that proposes that Earth's outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself. |
| reverse polarity | a magnetic field opposite to that which exists at present. |
| ridge push | a mechanism that may contribute to plate motion. it involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity. |
| rift valley | a long, narrow trough bounded by normal faults. it represents a region where divergence is taking place. |
| seafloor spreading | the process of producing new seafloor between two diverging plates. |
| slab pull | a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along. |
| subduction zone | a long, narrow zone where one lithospheric plate descends beneath another. |
| supercontinent | a large landmass that contains all, or nearly all, of the existing continents. |
| tectonic plate | a coherent unit of Earth's rigid outer layer that includes the crust and upper unit. |
| transform fault boundary | a boundary in which two plates slide past one another without creating or destroying lithosphere. |
| volcanic island arc | a chain of volcanic islands generally located a few hundred kilometers from a trench where active subduction of one oceanic slab beneath another is occuring. |
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