CH. 19 - Plate Tectonics

continental drift

the idea that continents move freely over Earth’s surface, changing their positions relative to one another.

seafloor spreading

a hypothesis that the sea floor forms at the crest of the mid-oceanic ridge, then moves horizontally away from the ridge crest toward an oceanic trench.

plate tectonics

the idea that Earth’s surface is divided into a few large, thick plates that move slowly and change in size.

Plate

a large, mobile slab of rock that is part of Earth’s surface

Lithosphere

the relatively rigid outer shell of Earth, includes the rocks of the crust (of either oceanic or continental character) and uppermost mantle

Asthenosphere

below the lithosphere; a zone that behaves in a ductile manner because of increased temperature and pressure.

divergent plate boundary

the plates move away from each other

convergent plate boundary

the plates move toward each other

transform plate boundary

the plates slide horizontally past each other.

rift valley

formed when movement accompanies tension at the ridge crest, cracking open the oceanic crust.

Subduction

The sliding of the sea floor beneath a continent or island arc.

Trench

a deep depression in the seafloor formed by the subduction of one tectonic plate beneath another at a convergent plate boundary.

island arc

a curved line of volcanoes that form a string of islands parallel to the oceanic trench

magmatic arc

formed by the magma that is created by ocean-continent convergence; a broad term used both for island arcs at sea and for belts of igneous activity on the edges of continents.

Convection

a circulation pattern driven by the rising of hot material and/or the sinking of cold material.

transform fault

The portion of a fracture zone between two offset portions of ridge crest.

polar wandering

the idea that ancient poles were in different positions from the present.

Mantle plume

narrow columns of hot mantle rock that rise through the mantle, much like smoke rising from a chimney.

hot spot

stationary areas of volcanic activity fueled by plumes of hot magma rising from deep within the Earth's mantle, independent of tectonic plate boundaries.

Benioff zone

a planar zone of earthquakes that occurs where a subducting tectonic plate bends and descends into the Earth's mantle.