14 terms

Ch 17 Plate Tectonics

Glencoe
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Convection (as it relates to plate tectonics)
Transfer of energy by the flow of 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 boundaries.
Continental Drift
Wegener's theory that Earth's continents had once been joined as a single landmass (Pangaea) that broke apart and slowly moved to where they are today.
Pangaea
Super-continent made of all the continents, prior to their break up.
Plate Tectonics
Theory that Earth's lithosphere (crust & rigid upper mantle) are broken into enormous moving slabs called plates.
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.
Convergent Boundary
Place/line where 2 plates move together or 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.
Ocean Ridge
A divergent boundary in the ocean where seafloor spreading occurs as magma rises, cools, forms new rock, forcing the 2 plates apart.
Rift Valley
A divergent boundary on land where continental crust begins to separate or "tear apart"
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.
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.
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.
Paleomagnetism
Study of Earth's magnetic field, based on magnetic iron in 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.
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.
Seafloor Spreading
Theory that states that new ocean crust is formed from rising magma at ocean ridges and destroyed at deep-sea trenches.