Geology chapter 3-4

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geology portrait of earth

abyssal plains

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

apparent polar wander patch

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.

bathymetry

Variation in depth.

continental drift

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

fracture zones

a narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mmid ocean ridge.
transform vault: the actively slipping part of a fracture zone

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 reversals

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

mid ocean ridges

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

pangaea

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

paleomagnetism

The record of ancient magnetism preserved in rock.

plate tectonics

The Earth's outer shell is broken into rigid plates that move, these moving plates change the face of the Earth.

mantle is transferred to the surfaces and back down again
interior and surface of the Earth are in constant motion
explains earthquakes, volcanoes, and continental drift

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.

seamounts

An isolated submarine mountain.

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.

trenches

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

volcanic arc

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

pillow basalt

magma quenched at sea floor

dike

preserved magma conduits

gabbro

deeper magma

guyot

a seamount that had a coral reef growing on top of it, so that now it is flat-crested
underwater plateau

accretionary prism

a wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accumulated on the overriding plate at a convergent plate margin

active continental margin

a continental margin that coincides with/near a plate boundary

asthenosphere

the layer of the mantle that lies between 100-150 km and 350 km deep; this layer is relatively soft and can flow when acted on by force. flows plastically

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

buoyancy

the upward force acting on a less dense object immersed or floating in denser material

collision

the process of two buoyant pieces of lithosphere converging and squashing together

continental margin

a continent's coastline

continental rift

a linear belt along which continental lithosphere stretches and pulls apart

continental rifting

the process by which a continent stretches and splits along a belt; if successful, this process separates a larger continent into two smaller continents separated by a divergent boundary

continental shelf

a broad, shallowly submerged region of a continent along a passive margin

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

dike

a tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock

divergent plate boundary

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

downgoing plate

a lithosphere plate that has been subducted at a convergent margin

earthquake belt

a relatively narrow, distinct belt of earthquakes that defines the position of a plate boundary

epicenter

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

focus

the location where a fault slips during an earthquake (hypocenter)

fracture zone

a narrow band of vertical fractures in the ocean floor that lie roughly at right angles to a mid-ocean ridge

global positioning system

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

lithosphere

the relatively rigid, nonflowable, outer 100-150- thick layer of the Earth; comprising the crust and the top part of the mantle

magma chamber

a space below ground filled with molten rock

mantle plume

a column of very hot rock rising up through the mantle

marginal sea

a small ocean basin created when sea-floor spreading occurs behind an island arc

mid ocean ridge

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

passive margin

a continental margin that is not a plate boundary

pillow basalt

glass-encrusted basalt blobs formed when magma is extruded on the sea floor and cools very quickly

plate boundary

the border between two adjacent lithosphere plates

plate boundary volcano

a volcanic arc or mid-ocean ridge volcano, formed as a consequence of movement along the border between two adjacent lithosphere plates

plate interior

a region away from the plate boundaries that consequently experiences few earthquakes

relative plate velocity

the movement of one lithosphere plate with respect to another

ridge axis

the crest of a mid-ocean ridge; the ridge axis defines the position of a divergent plate boundary

slab pull force

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

subduction

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

theory of plate tectonics

the theory that the outer layer of the Earth (the lithosphere) consists of separate plates that move with respect to one another

transform fault

a fault marking a transform plate boundary; along mid-ocean ridges; these are the actively slipping segment of a fracture zone between two ridge segments

transform plate boundary

a boundary at which one lithosphere plate slips laterally past another

trench

a deep elongate trough bordering a volcanic arc; 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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