Plate Tectonics and Earth Structure

These flashcards cover key vocabulary and concepts related to plate tectonics and Earth's structure from the lecture notes.

lithosphere

The relatively rigid, nonflowable outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle.

asthenosphere

The layer of the mantle that lies between 100–150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force.

lithospheric mantle

The part of a plate, below the crust, in which mantle is cool enough to behave rigidly.

lithosphere plate

One of many distinct pieces of the lithosphere that are separated from one another by breaks (plate boundaries).

plate

One of about 20 distinct pieces of the relatively rigid lithosphere.

plate boundary

The border between two adjacent lithosphere plates.

active margin

A continental margin that is also a plate boundary.

hypocenter (focus)

The place within the Earth where earthquake energy originates.

epicenter

The point on the surface of the Earth directly above the focus of an earthquake.

seismic belts (seismic zones)

The relatively narrow strips of crust on the Earth at which most earthquakes occur.

divergent boundary

A boundary at which two lithosphere plates move apart from each other, marked by mid-ocean ridges.

black smoker

The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge.

convergent boundary

A surface across which two plates move toward each other so that one plate sinks beneath the other.

subduction

The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate.

trench

A deep, elongate trough bordering a volcanic arc; it defines the trace of a convergent plate boundary.

Wadati-Benioff zone

A sloping band of seismicity defined by intermediate- and deep-focus earthquakes at a convergent plate boundary.

accretionary prism

A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate.

volcanic arc

A curving chain of active volcanoes formed adjacent to a convergent plate boundary.

volcanic island arc

The volcanic island chain that forms on the edge of the overriding plate where one oceanic plate subducts beneath another.

fracture zone

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge.

transform boundary

A boundary at which one lithosphere plate slips laterally past another.

triple junction

A point where three lithosphere plate boundaries intersect.

hot spot

A location at the base of the lithosphere where temperatures can cause melting and igneous activity.

hot-spot track

A chain of now-dead volcanoes transported off the hot spot by the movement of a lithosphere plate.

mantle plume

A column of very hot rock that rises up through the mantle.

continental rift

A linear belt along which continental lithosphere stretches and pulls apart.

rifting

The process by which continental lithosphere stretches horizontally and thins vertically.

suture

The contact defining the boundary of what were two separate crustal blocks, prior to collision.

collision

The process of two buoyant pieces of lithosphere converging and squashing together.

upwelling

The upward flow of air or water.

downwelling

The downward movement of a volume of material; downwelling in the mantle carries cooler, denser mantle deeper.

ridge-push force

A process in which gravity causes the elevated lithosphere at a mid-ocean ridge to push on lithosphere further away.

slab-pull force

The force that downgoing plates apply to oceanic lithosphere at a convergent margin.

relative plate velocity

The movement of one lithosphere plate with respect to another.

absolute plate velocity

The movement of a plate relative to a fixed point in the mantle.