"Ch 17 Plate Tectonics"

Island Arc

Formed above an oceanic-oceanic convergent boundary when volcanoes become tall enough to break the surface of the water. Examples: Aleutian Islands, Japan, Phillipines

Deep Sea Trench

Formed at convergent boundaries when subduction occurs and the more dense oceanic plate slips under another plate. The deepest one is by the Mariana Islands.

Convergent Boundary

2 plates collide. There are 3 subtypes. Oceanic to oceanic resulting in subduction, volcanoes and island arcs like Aleutian Islands. Oceanic to continental resulting in subduction, volcanoes, mountains like Andes Mountains in South America. Continental to continental resulting in earthquakes and folded (very high) mountains like Himalayas.

Transform Boundary

2 plates slide horizontally past each other. Example location San Andreas Fault in California.

magnetometer

A device that can detect small changes in magnetic fields

rift valley

A long, narrow valley in Earth's crust where two continental plates are separating or between two faults.

slab pull

A mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along

divergent boundary

A plate boundary where two plates move away from each other A boundary along which two tectonic plates move apart, characterized by either a mid-ocean ridge or a continental rift valley.

convergent boundary

A region where plates are pushing together and where a mountain range, island arc, and/or trench will eventually form; often a site of much seismic and volcanic activity.

isochron

An imaginary line on a map that shows points that have the same age and are formed at the same time

continental-continental convergent boundary

At a convergent boundary, when the two plates are the same density, so neither can sink. They crumple and push upwards, forming mountain ranges like the Himalayas.

Magnetic Reversal

Change in Earth's magnetic field. The iron in the basalt on the ocean floor indicate the Earth's magnetic field has reversed several times.

Ocean Ridge

Divergent boundary in ocean where seafloor spreading occurs as magma rises, cools, forms new rock, forcing the 2 plates apart.

Rift Valley

Divergent boundary on lad where continental crust begins to separate or "tear apart"

Folded (Very High) Mountains

Extremely high mountains formed when 2 continental plates converge (collide). Because the continental plates have similar density there is no subduction and plates are crumpled & forced up instead.

Wegener

German scientist who developed theory of Continental Drift. No one believed at first, because he couldn't explain how the continents moved.

magnetic reversal

Happens when the flow in the outer core changes, and Earth's magnetic field changes direction

seafloor spreading

Hess's theory that new seafloor is formed when magma is forced upward toward the surface at a mid-ocean ridge

tectonic plate

Large rocky masses or plates that cover the surface of the Earth like jagged jigsaw pieces. Some are on the surface (Continents and some islands) or under the oceans (oceanic plates). They are moving slowly, shifted by the flow of magma. Where they collide or move against each other are highly tectonically active (earthquakes, volcanoes) where areas that they are moving apart are often areas where new plate is formed (mid-oceanic rifts, or rift valleys).

Isochron

Line on a map that connects points of equal age that were formed at the same time. Isochron maps have been used to map the age of the ocean floor - Figure 17-11 p.453

Magnetic Symmetry

Opposite sides of an ocean ridge have mirror-image patterns of magnetic reversals.

transform boundary

Place where two tectonic plates slide horizontally past each another that is characterized by long faults and shallow earthquakes.

Divergent Boundary

Place/line where 2 plates are moving apart. Most are on the bottom of the ocean floor where ocean ridges, volcanoes, and earthquakes are found. If the divergent boundary is on land, a rift valley is found. Examples: Mid-Atlantic Ridge and East African Rift Valley.

Subduction

Process where the more dense tectonic plate slips beneath another tectonic plate. Is where rocks are "recycled". Rocks may "melt" as buried deeper, leading to volcanoes.

Paleomagnetism

Study of Earth's magnetic field, based on magnetic iron of basalt on the ocean floor. The iron lines up and "points" in the direction of the Earth's magnetic field when the magma cooled and formed rock.

ridge push

Tectonic process associated with convection currents in Earth's mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone

Theory of Plate Tectonics

Theory that Earth's lithosphere (crust & rigid upper mantle) are broken into enormous moving slabs called plates.

Seafloor Spreading

Theory that states that new ocean crust is formed from rising magma at ocean ridges and destroyed at deep-sea trenches.

Convection (as it relates to plate tectonics)

Transfer of energy by the flow if a heated material. Convection currents in the asthenosphere (soft, plastic-like part of mantle) are thought to cause plate movement. Convection cycle rises at the mid-ocean ridges of divergent boundaries and sinks at the deep-sea trenches of convergent bondaries.

continental drift

Wegener's hypothesis that Earth's continents had once been joined as a single landmass (Pangaea) that broke apart and slowly moved to where they are today.

Pangea

a super continent made up of all the continents

oceanic-continental convergent boundary

more dense oceanic plate dives under continental plate. forms a trench. causes volcanoes, and earthquakes (Andes Mountains)

oceanic-oceanic convergent boundary

older plate slide beneath younger plate, strong to moderate earthquakes are common. Island arcs may parallel the trench, deep ocean trench forms (marianas trench)

paleomagnetism

the study of changes in Earth's magnetic field, as shown by patterns of magnetism in rocks that have formed over time