Convergent Margin		A theory proposed during the early 1960's in which lateral movement of the oceanic crust away from midocean ridges was postulated. (Seafloor Spreading)
Hot Spot		The zone where plates meet as they move toward each other. (Convergent Margin)
Plate Triple Junction		Long, narrow, very deep, and arcuate basins in the seafloor. (Trenches)
Continental Drift		A fracture in the lithosphere along which two plates slide past each other. (Transform Fault Margin)
Continental Shelf		A continental margin in a plate interior. (Passive Margin)
Spreading Center		Broad flat expanses of seafloor, 3 to 6 km deep. Young oceanic plate grows dense and subsides as it cools. Abyssal floors form after an oceanic plate has cooled enough for heat rising from the deep mantle to balance heat loss through the seafloor.(Abyssal Floor)
Continental Slope		A region of gently changing slope where the floor of the ocean basin meets the margin of a continent. (Continental Rise)
Subduction Zone		An isolated submerged volcanic mountain standing more than 1000 m above the seafloor. (Seamount)
Geothermal gradient		The new, growing edge of a plate. Coincedent with a midocean ridge. (Spreading Center)
Divergent Margin		A fixed point on the Earth's surface defined by long-lived volcanism. (Hot Spot)
Passive margin		The rate of increase of temperature downward in Earth. (Geothermal Gradient)
Continental Rise		A pronounced slope beyond the seaward margin of the continental shelf. (Continental Slope)
Tranches		Junction between three plate spreading edges. The angle between any two edges is approximately 120 degrees. (Plate Triple Junction)
Seafloor Spreading		The ideal property of flotational balance among segments of the lithosphere. (Principle of Isostasy)
Magnetic Latitude		A convergent plate margin where two plates collide. (Collision Zone)
Abyssal Floor		The slow, lateral movements of continents across Earth's surface. (Continental Drift)
Mantle Convection		The latitude of a place on the Earth with respect to the magnetic poles. (Magnetic Latitude)
Transform Fault Margin		A continental coastline that is coincident with a convergent plate boundary. (Active margin)
Collision Zone		A submerged platform of variable width that forms a fringe around a continent. (Continental Shelf)
Principle of Isostasy		The linear zone along which a plate of lithosphere sinks down into the asthenoshpere. (Subduction Zone)
Ridge Push		A fracture in the lithosphere where two plates move apart. (Divergent Margin)
Active Margin		Convection of Earth's mantle, driven both by the thermal buoyance of hot rock rising from the depth and by sinking of cooler, denser lithosphere. (Mantle Convection)
Seamount		The tendency for young oceanic lithosphere to slide laterally down the slope of a midocean rige under the influence of gravity, thereby pushing the rest of the plate away from the ridge. (Ridge Push)
Slab Pull		The tendency for sinking lithosphere at a convergent plate boundary to pull the rest of the plate laterally into the convergent zone. (Slab Pull)