!GLG 101-Illustrated Vocabulary-Chapter 18
!Plate Tectonics
copyright 2003-Roger Weller
!accretion
*the process of slowly adding on; applied to the theory of continental accretion where
continents have gotten larger with time as new land is added to the margins of continents.
!Aleutian Islands, Alaska
*a prominent curved chain of volcanic islands extending from Alaska westward.
Structurally, these islands are an island arc adjacent to a subduction zone.
!allochthonous terrane
*a large mass of land that has moved a substantial distance before reaching its present
position as part of a continent.
!Alps
*a prominent mountain range in southern Europe
!Andes Mountains of South America
*a prominent mountain chain that extends along the western side of South America. The
mountains consist of fault blocks and volcanoes which were created by an oceanic plate
being subducted beneath the mountain chain.
!Appalachian Mountains
*a low mountain range extending from Georgia up through Maine and continuing on
through eastern Canada.
!authocthonous terrane
*a landmass that is in the location where it was formed, in contrast to an allochthonous
terrane that was moved into its present position from some place else.
!Baja California
*a prominent peninsula in Mexico that is bordered on one side by the Pacific Ocean and
by the Gulf of California on the other. It is a terrane that broke loose from the main
landmass of Mexico and is migrating northwesterly along the western side of North
America assisted by the San Andreas fault.
!Benioff zone
*the earthquake zone associated with a subduction zone.
!bouyancy
*objects denser than the fluid in which they are placed will sink; objects less dense than
the fluid in which they are placed will float. A dense object placed within a fluid will
have its apparent weight decreased equal to the weight of an equal volume of water that it
displaces.
!Cascades
*a chain of andesitic volcanoes extending from California to Britsh Columbia; contains
Mt. Rainier, Mt. St. Helens, Lassen Peak, Crater Lake, and others.
!Circum Pacific belt
*the collection of earthquake epicenters that encircle the Pacific Ocean.
!Colorado Plateau
*a large uplifted area that covers portions of Arizona, Utah, Colorado, and New Mexico.
!Columbia River basalts
*huge outpourings of fluid basaltic lava inundated a large area of the Pacific Northwest
of the United States.
!continental-continental plate boundary
*If this is a divergent boundary, a rift zone will form above the boundary; if it is a
covergent boundary, a folded mountain range will be pushed uo, such as the
Appalachians or the Ural mountains.
!continental crust
*a portion of the Earth's crust that is thicker and less dense than oceanic crust.
Consequently, this type of crust floats at a higher elevation and protrudes above sea level
to form continents.
!continental drift
*a theory that proposes that continents were once attached together but have since split
and have moved apart; this concept preceeded the modern concept of plate tectonics.
!continental rifting
*a divergent plate boundary develops beneath a continent and the continent starts to pull
apart. A modern example is the East Afric
!convergence
*where two objects keep getting closer together
!convergent boundary
*one of the three types of tectonic plate boundaries; crustal plates are coming towards
each other.
!crustal plates
*the crust of the Earth is brittle and is broken into large pieces.
!curie point of magnetite
*the temperature above which magnetite loses its magnetic properties. For magnetite,
this temperature is 580 degrees Celsius. If above 580 degrees Celsius, magnetite crystals
will align their orientation with the magnetic field of the Earth when cooled below this
temperature.
!divergent boundary
*the two crustal plates at a boundary are moving away from each other.
!East African Rift Valley
*a long rift valley marked by volcanoes and lakes located along the southeastern portion
of Africa.
!East Pacific Rise
*an undersea spreading ridge located in the southern and eastern portions of the Pacific
basin
!Galapagos Islands
*a group of small shield volcanoes that form islands in the eastern Pacific Ocean,
associated with a hot spot.
!Gondwanaland
*the ancient landmass consisting of the southern continents: South America, Africa,
Australia, India, and Antactica
!Hawaiian Islands
*these islands are the tops of shield volcanoes that were formed when the Pacific plate
moved over an active hot spot.
!Himalaya Mountains
*the tallest moutain range on Earth, formed where India is crashing into Asia.
!hot spot
*a term applied to a small region in which a prolific amount of magma is being generated
over a long interval of geologic time; since crustal plates move over these buried sources
of magma, the result is a trail of volcanoes and/or intrusions on the crustal plate.
!island arc
*a curved chain of volcanic islands ajacent to an oceanic trench and overlying a
subduction zone
!Laurasia
*the ancient landmass consisting of Asia, Europe, and most of North America
!magnetic
*a physical property in which a material is attracted to a magnet
*[Magnetite-Lodestone]
!magnetic anomaly
*a spot on the ocean floor where the oceanic crust is magnetized in a direction opposite to
today's orientation of the magnetic poles
!magnetic reversal
*the Earth's magnetic field changes direction; the North and South magnetic poles trade
positions.
!magnetite
*the most common occurring mineral that is attracted to a magnet; a black mineral made
of iron oxide.
*[Magnetite-Lodestone]
!magnetometer
*a highly sensitive device that can detect changes in the Earth's magnetic field
!mantle plume
*hot, low density molten (or semi-molten) material rises from the mantle and comes up
underneath the crust.
!Mid-Atlantic Ridge
*a spreading ridge where two crustal plates are moving apart; this underwater ridge goes
straight up the middle of the Atlantic Ocean
!oceanic crust
*the crust of the Earth beneath the oceans; typically only 2 to three miles thick.
!oceanic-contintental plate boundary
*if this is a convergent boundary, the oceanic crustal slab is subducted beneath the
continental crust at about a 30 degree angle.
!oceanic-oceanic plate boundary
*If this is a divergent plate boundary, an oceanic ridge will form at the boundary; if it is a
convergent boundary, the oceanic plate on one side of the boundary will be subducted
under the other at a steep angle.
!oceanic ridge
*an underwater ridge formed where two crustal plates are pulling apart. The MidAtlantic Ridge is a good example of an oceanic ridge.
!orogenic belt
*a long line of mountains that were produced by a common tectonic event
!orogeny
*a mountain building event
!Pacific Plate
*the largest of the crustal plates, it is covered by the Pacific Ocean and is nearly
surrounded by subduction zones.
!partial melting
*as a subducted slab of crust moves down a subduction zone, those minerals with the
lowest melting temperatures melt first.
!pillow lava
*underwater eruptions of basaltic lava form pillow-like shapes
!Pinacates Volcanic Field, Mexico
*a volcanic hot spot in northern Sonora, Mexico, consisting several large maars,
numerous cinder cones, and fresh appearing basaltic lava flows.
*[Crater Elegante from the air]
*[Cinder cone and lava flow]
!plastic flow
*under pressure, a material flows instead of breaking.
!plate tectonics
*a concept in which the crust of the Earth is considered to be brittle and is broken into
several large pieces (tectonic plates). Most of the seismic activity on the Earth today is
located at the edges of the plates where the plates are either diverging, converging, or
sliding past each other.
!regional metamorphism
*a large area of a continent has been metamorphosed due to a major tectonic event such
as collision of continents.
!rift valley
*where crustal plates are pulling apart (divergence), long graben depressions created by
rifting form valleys.
!Ring of Fire
*the collection of volcanoes that are found encircling the Pacific Ocean.
!San Andreas fault, California
*a prominent strike-slip fault extending from near Yuma, Arizona, running northeast of
Los Angeles up through San Francisco. This fault separates the Pacific plate on the west
from the North American plate to the east.
*[Map-California-Los Angeles]
*[Map-California-San Francisco]
!seafloor spreading
*is occurs along the crest of oceanic ridges where the oceanic crust is being pulled apart
and lava is filling the fissures, thereby creating new seafloor.
!spreading center volcanism
*along an oceanic ridge where seafloor spreading is occurring, lava emerges where the
oceanic plates are pulling apart and opening up fissures.
!subduction zone
*when two crustal plates converge, one crustal plate often dives beneath the other at an
angle between 30 degrees and 60 degrees from the horizontal.
!subduction zone volcanics
*In a subduction zone, a slab of oceanic crust with sediments is subducted down into the
hot mantle where low temperature minerals in the slab start to melt. The newly formed
magma rises to the surface adjacent to the trench to produce volcanoes.
!terrane
!thermal convection
*within the mantle of a planet, hot fluid material rises because of its lower density, while
cold material sinks because of its higher density
!transform boundary
*one of the three kinds of plate tectonics boundaries; where plates slide past each other
!transform fault
*a strike-slip fault where blocks on oppsite sides of a fault move in opposite horizontal
directions.
!trench
*a depression on the ocean floor where oceanic crust is being subducted
!triple junction
*three oceanic spreading ridges radiate from a common point.
!Ural Mountains
*a fold mountain range that separates Europe from Asia
!Wegener, Alfred
*the geologist who developed and promoted the concept of continental drift.
!Wilson, J. Tuzo
*the Canadian geologist who promoted and helped to develop the concept of plate
tectonics.