Chapter 02 Vocab Flashcards
absolute plate velocity
The movement of a plate relative to a fixed point in the mantle.
abyssal plain
A broad, relatively flat region of the ocean that lies at least 4.5 km below sea level.
accretionary prism
A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate at a convergent plate margin.
active 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.
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.
bathymetry
Variation in depth.
black smoke
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.
collision
The process of two buoyant pieces of lithosphere converging and squashing together.
continental drift
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.
continental shelf
A broad, shallowly submerged fringe of a continent; ocean-water depth over the continental shelf is generally less than 200 meters; the widest continental shelves occur over passive margins.
convergent 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 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.
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.
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
An imaginary vector that points from the north magnetic pole to the south magnetic pole of a magnetic field.
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 ends of a magnetic dipole; all magnetic dipoles have a north pole and a south pole.
magnetic-reversal chronology
The history of magnetic reversals through geologic time.
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.
mantle plume
A column of very hot rock rising up through the mantle.
mid-ocean ridge
A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.
paleomagnetism
The record of ancient magnetism preserved in rock.
paleopole
The supposed position of the Earth’s magnetic pole in the past, with respect to a particular continent.
Pangaea
A supercontinent that assembled at the end of the Paleozoic Era.
passive margin
A continental margin that is not a plate boundary.
plate boundary
The border between two adjacent litho sphere plates.
plate tectonics
The theory that the outer layer of the Earth (the lithosphere) consists of separate plates that move with respect to one another.
relative plate velocity
The movement of one litho sphere plate with respect to another.
rifting
The process by which a continent stretches and splits along a belt; if it is successful, rifting separates a larger continent into two smaller continents separated by a divergent boundary.
sea-floor spreading
The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.
seamount
An isolated submarine mountain
slab-pull force
The force that downgoing plates (or slabs) apply to oceanic lithosphere at a convergent margin.
spreading rate
The rate at which sea floor moves away from a mid-ocean ridge axis, as measured with respect to the sea floor on the opposite side of the axis.
subduction
The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate.
transform boundary
A boundary at which one litho sphere plate slips laterally past another.
trench
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.
