GRG301C: Ch. 15, Plate Tectonics

a subdivision of the mantle situated below the lithosphere
continental drift
a hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single supercontinent
continental rift
a linear zone along which continental lithosphere stretches and pulls apart
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, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle
Curie point
the temperature above which a material loses its magnetization
divergent plate boundary
a boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor
fracture zone
linear zone of irregular topography on the deep-ocean floor; follows transform faults and their inactive extensions
a proposed concentration of heat in the mantle capable of introducing magma that in turn extrudes onto Earth's surface
the rigid outer layer of Earth, including the crust and upper mantle
lithospheric plate
a coherent unit of Earth's rigid outer layer that includes the crust and upper mantle
a sensitive instrument used to measure the intensity of Earth's magnetic field at various points
magnetic reversal
a change in Earth's magnetic field from normal to reverse or vice versa
magnetic time scale
the detailed history of Earth's magnetic reversals developed by establishing the magnetic polarity of lava flows of known age
mantle plume
a mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity
normal polarity
a magnetic field the same as that which presently exists
oceanic ridge
a continuous mountainous ridge on the floor of all the major ocean basins
the natural remnant magnetism in rock bodies
the proposed supercontinent that 200 million years ago began to break apart and form the present landmasses
partial melting
the process by which most igneous rocks melt
plate tectonics
the theory that proposes Earth's outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
reverse polarity
a magnetic filed opposite to that which presently exists
ridge push
a mechanism that may contribute to plate motion; involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity
a region of Earth's crust along which divergence (separation) is taking place
seafloor spreading
the hypothesis first proposed in the 1960s by Harry Hess, suggesting that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence
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 zones
a long, narrow zone where one lithospheric plate descends beneath another
a huge landmass that consists of all, or nearly all, of the existing continents combined into one
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 there is active subduction of one oceanic plate beneath another