earth science ch. 5
plate tectonics: a scientific theory unfolds
Terms
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- partial melting
- the process by which most igneous rocks melt. since individual minerals have different melting points, most igneous rocks melt over a temp. 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
- seafloor spreading
- the process of producing new seafloor between two diverging plates
- magnetometer
- a sensitive instrument used to measure the intesity of earths magnetic field
- lithosphere
- the rigid outer layer of earth, including hte crust and upper mantle
- normal polarity
- a magnetic field that is the same as that which exists at present
- transform fault
- conservative; a major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates
- convergent boundary
- destructive; 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 an overriding plate
- 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
- island arc [ volcanic island arc ]
- a chain of volcanic islands generally located a few hundred kilometers from a trench whre there is active subduction of none oceanic plate beneath another
- fracture zone
- linear zone of irregular topography on the deep-ocean floor that follows transform faults and their inactive extensions
- 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
- divergent boundary
- constructive; a region where the rigid plates are moving apart, typified by the mid-oceanic ridges
- continental drift
- a theory that originally proposed that the continents are rafted about; it has been replaced by plate tectonics theory
- asthenosphere
- a subdivision of the mantle situated below the lithosphere; rock within this zone is easily deformed
- fossil magnetism [ paleomagnetism ]
- the natural remnant magnetism in rock bodies; the permanent magnetization acquired by rock that can be used to determine tht location of the magnetic poles and the latitude of hte rock at the time it became magnetized
- continental volcanic arc
- mountains formed by igneous activity associated with the subduction of oceanic lithosphere beneath a continent
- curie point
- the temp. above which a material loses its magnetization
- magnetic reversal
- a change in polarity of earths magnetic field that occurs over time intervals of roughly 200,000 yrs
- plate
- one of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere
- pangaea
- the proposed super-continent, which 200 million years ago began to break apart and form the present landmasses
- hot spot
- a concentration of heat in the mantle capable of production magma, which in turn extrudes onto earths surface; the intraplate volcanism that produced the Hawaiian islands is one example
- slab suction
- one of the driving forces of plate motion, it arises from the drag of the subducting plate on the adjacent mantle; it is an induced mantle circulation that pulls both the subducting and overriding plates toward the trench
- subduction zone
- a long, narrow zone where one lithospheric plate descends beneath another
- rift [ rift valley ]
- a region of earths crust along which divergence is taking place
- magnetic time scale
- the history of magnetic reversals through geologic time
- 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
- transform boundary
- conservative; a boundary in which two plates slide past one another without creating or destroying lithosphere
- deep ocean trench
- a narrow, elongated depression on the floor of the ocean
- mantle plume
- a source of some intraplate basalic magma, these structures originate at great depth and , upon reaching the crust, spread laterally, creating a localized volcanic zone called a hot spot
- oceanic ridge system [ mid-ocean ridge ]
- a continuous elevated zone on the floor of all the major ocean basins and varying in width from 500-5000 kilometers; the rifts at the crets of these ridges represent divergent plate boundaries