A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 km and in some regions extends as deep as 700 km. The rock within this zone is easily deformed.
A theory that originally proposed that the continents are rafted about. It has essentially been replaced by the plate tectonics theory.
Continental Volcanic Arc
Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent.
Convergent Plate Boundary
A boundary in which two plates move together, causing one of the slabs of the lithosphere to be consume into the mantle as it descends beneath on an overriding plate.
The temperature above which a material loses its magnetization.
An elongated depression in the seafloor produced by bending of oceanic crust during subduction.
Divergent Plate Boundary
A region where the rigid plates are moving apart, typified by the mid-oceanic ridges.
AKA 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 became magnetized.
A zone of prominent linear breaks in the oceanic crust that join two segments of an oceanic ridge. They are present approximately every 100 km along the trend of a ridge axis.
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.
A chain of volcanic islands generally located a few hundred km from a trench where active subduction of one oceanic slab beneath another is occuring.
The rigid outer layer of Earth, including the crust and upper mantle.
A switch of Earth's north and south magnetic poles.
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.
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 5000 km. The rifts at the crests of ridges represent divergent plate plate boundaries.
AKA fossil magnetism, 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.
The proposed supercontinent that, 200 million years ago, began to break apart and form the present landmasses.
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 has occurred, a melt with a higher silica content results.
One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere.
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.
A magnetic field opposite to that which exists at present.
A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.
A region of Earth's crust along which divergence is taking place.
The process of producing new seafloor between two diverging plates.
A mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and pulls the trailing lithosphere along.
Induced mantle circulation that pulls both subducting and overriding plates toward a trench.
A long, narrow zone where one lithospheric plate descends beneath another.
A boundary in which two plates slide past one another without creating or destroying lithosphere.
Volcanic Island Arc
AKA island arc, a chain of volcanic islands generally located a few hundred km from a trench where active subduction of one oceanic slab beneath another is occurring.