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plate tectonics

global dynamics having to do with the movement of a small number of semirigid sections of Earth's crust, with seismic activity and volcanism occuring primarily at the margins of these sections. this movement has resulted in changes in the geographic positions of continents and the shape and size of ocean basins.

Alfred Wegener

german meteorlogist and geophsicist. first to advance the idea of mobile continents in 1912.

Continental drift

a term applied to early theories supporting the possibility the continents are in motion over Earth's surface


an ancient supercontinent of the geologic past that contained all earth's continent


a large, ancient ocean that surround pangaea

Tethys sea

an ancient body of water that seperated Laurasia to the north and Gondwanaland to the south. its location was approximately that of the present Alpine-Himalayan mountain system

ice age

the most recent glacial period, which occured during the Pleistocene epoch


an extinct, presumably aquatic reptile that lived about 250 million years ago, and located only in eastern south america and western africa

Magnetic field

a condition found in the region around a magnet or an electric current, characterized by the existence of a detectable magnetic force at every point in the region and by the existence of magnetic poles


a naturally magnetic iron mineral


study of earths ancient magnetic field

magnetic dip

degree to which a magentite particle points into earth

polar wandering curves

a curve that shows the change in the position of a pole through time


the directional orientation of the magnetic field

magnetic anomalies

distortions of the regular pattern of earths magnetic field resulting from the various magnetic properties of local concentrations of ferromagnetic minerals in earths crust

sea floor spreading

a process producing the lithosphere when convective upwelling of magma along the oceanic ridges moves the ocean floor away from the ridge axes at rates between 2 to 12 centimeters per year

convection cells

a circular moving loop of matter involved in convective movement

mid-ocean ridge

continuous underwater mountain range that winds through every ocean basin in the world and resembles the seam of a baseball

spreding center

a divergent plate boundary

ocean trenches

deepest parts of the ocean floor and resemble a narrow crease or trough


the process by which one lithospheric plate descends beneath another as they converge

subduction zone

a long narrow region beneath earths surface in which subduction takes place


the zone between the core and crust of earth, rich in ferromagnesium minerals


the quantity of heat flow to earths surface per unit of time


the outer layer of earths structure, including the crust and the upper mantle to a depth of about 200 km, major components involved in plate techtonic movement


a plastic layer in the upper mantle 80 to 200 km deep that may allow lateral movement of lithospheric plates and isostatic adjustments

divergent boundaries

a lithospheric plate boundary where adjacent plates diverge, producing an oceanic ridge or rise

convergent boundaries

a lithospheric plate boundary where adjacent plates converge, producing ocean trench-island arc systems, ocean trench-continental volcanic arcs, or folded mountain ranges

transform boundaries

the boundary between two lithospheric plates formed by a transform plate

rift valley

a deep fracture or break, about 25 to 50 km wide, extending along the crest of mid-ocean ridge


the movement of two plates in opposite directions such as along a divergent boundary

oceanic rises

gently sloping and fast-spreading parts of the mid-ocean ridge

east pacific rise

oceanic rise between pacific and nazca plate. broad, low, gentle swelling of the sea floor with a small, indistinct central rift valley

oceanic ridges

steeper-sloping and slowe-spreading areas of the mid ocean ridge

mid atlantic ridge

oceanic ridge between south american and african plates. tall, steep, rugged oceanic ridge

seismic moment magnitude

earthquake intensity is measured on a scale, which reflects the energy released to create very long period seismic waves

volcanic arc

melting in the subduction zone causes an arc shaped row of highly active and explosively erupting volcanoes that parallel the trench

continental arc

an arc shaped row of active volcanoes produced by subduction that occurs along convergent active continental margins

island arc

a linear arrangement of islands, many of which are volcanic, usually curved so that the concave side faces a sea seperating the islands from a continent. the convex side faces the open ocean and is bounded by a deep-ocean trench

transform faults

a fault with side to side motion that offsets segments of a mid-ocean ridge

oceanic transform fault

transform fault that occurs wholly on the ocean floor

continental transform fault

transform fault that cuts across a continent

transform faulting

movement of one plate past another-produces shallow but often strong earthquakes in the lithosphere

san andres fault

continental transform fault that runs from the gulf of california past san francisco and beyond into northern california


areas of intense volcanic activity that remain in more or less the same location over long periods of geologic time and are unrelated to plate boundaries

mantle plumes

columnar areas of hot molten rock that arise from deep within the mantle


a chain of extinct volcanoes that is progressively older as one travels away from a hotspot


tall volcanic peaks on the ocean floor

tablemounts or guyots

tall volcanic peaks conical on the top on the bottom of the ocean floor

coral reef

a calcareous organic reef composed significantly of solid coral and coral sand

fringing reefs

intially develop along the margin of a landmass where the temperature, salinity, and turbidity of the water are suitable for reef builiding corals

great barrier reef

largest reef system in the world.


a ring-shaped coral reef growing upward from a submerged volcanic peak. it may have low-lying islands composed of coral debris


study of historical changes of continental shapes and positions

continental accretion

growth or increase in size of a continent by gradual external addition of crustal material

wilson cycle

a model that uses plate techtonic processes to show the distinctive life cycle of ocean basins during their formation, growth, and destruction

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