Essentials of Geology, 3: Chapter 2 Flashcards flashcards |

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absolute plate velocity

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

abyssal plain

A broad, relatively fl at region of the ocean that lies at least 4.5 km below sea level.

active continental margin

A continental margin that coincides with a plate boundary.

apparent polar-wander path

A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly fixed.


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.

black smoker

The cloud of suspended minerals formed where hot water spews out of a vent along a mid-ocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools.


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

continental drift hypothesis

The idea that continents have moved and are still moving slowly across the Earth's surface.

continental rift

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

convergent plate boundary

A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct.

divergent plate boundary

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

fracture zone

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.

global positioning system (GPS)

A satellite system people can use to measure rates of movement of the Earth's crust relative to one another, or simply to locate their position on the Earth's surface.

hot spot

A location at the base of the lithosphere, at the top of a mantle plume, where temperatures can cause melting.

hot-spot track

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


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

lithosphere plate

A portion of the outer, relatively rigid layer of the Earth; most seismic activity happens at the boundaries of plates, while the interior of a plate is relatively stable.

magnetic anomaly

The difference between the expected strength of the Earth's magnetic field at a certain location and the actual measured strength of the field at that location.

magnetic declination

The angle between the direction a compass needle points at a given location and the direction of true north.

magnetic dipole

A magnetic entity that has a north and south end.

magnetic inclination

The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth's surface.

magnetic pole

The north or south ends of a magnet; field lines point straight down at the pole.

magnetic reversal

The change of the Earth's magnetic polarity; when a reversal occurs, the field flips from normal to reversed polarity, or vice versa.

magnetic-reversal chronology

The history of magnetic reversals through geologic time.

mantle plume

A column of very hot rock rising up through the mantle.

marine magnetic anomaly

An unusually strong or unusually weak magnetic field, as measured over the sea floor; in map view, they look like stripes that are parallel to the mid-ocean ridge.

mid-ocean ridge

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.


The record of ancient magnetism preserved in rock.


The supposed position of the Earth's magnetic pole in the past, with respect to a particular continent.


A supercontinent that assembled at the end of the Paleozoic Era.

passive margin basin

A thick accumulation of sediment along a tectonically inactive coast, formed over crust that stretched and thinned when the margin first began.


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

plate boundary

The border between two adjacent lithosphere plates.

relative plate velocity

The movement of one lithosphere plate with respect to another.

ridge-push force

The force that drives plates away from a mid-ocean ridge; it is caused by the fact that the ridge is elevated relative to the regions of oceanic plate away from the ridge.


The process by which continental lithosphere stretches and breaks apart; rifting produces normal faults and, commonly, volcanism.

sea-floor spreading

The gradual widening of an ocean basin as oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.


An isolated submarine mountain.

slab-pull force

The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin.


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

transform plate boundary

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


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

triple junction

A point where three lithosphere plate boundaries intersect.

volcanic arc

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

Wadati-Benioff zone

A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary.

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