Chapter 2 - Global Tectonics: Our Dynamic Planet & Chapter 20 - Earth Through Geologic Time Flashcards
Continental Drift
Theory by Alfred Wegener (1912); stated that continents plow slowly through solid rock of ocean floor; widely rejected
Plate Tectonics
Ocean floor drifts as well as continents
Isostasy
Continents/mountains stand high because they are thick and light ocean basins are topographically low because they are thin and dense
Explanation for vertical motions of earth’s surface
Isostasy
Explanation for horizontal motions of earth’s surface
Plate tectonics
Geographic Edge of Oceans
Shoreline
Geographic Edge of Tectonic Boundary
Where oceanic and continental crust meet
Abyssal Floors
large, smooth areas of sea floor
Mid-Ocean Ridge/Rift Valley
Form continuous feature greater than 60,000 km long. Mark where two oceanic plates spread apart and new lithosphere forms
Passive Margins
Little earthquake and/or volcanic activity
Continental Shelf
Shoreline to flooded margin
Continental Slope
tectonic boundary at bottom of steeper
Continental Rise
Gentle slope at bottom. Oceanic and continental lithosphere remain connected
Active Margins
earthquakes and/or volcanoes common activity
Mantle convection
circulation of hot rock from mantle to surface layers. Rock cools at surface, moves laterally, and sinks back down again.
Geothermal Gradient
Increase in temperature with depth
Adiabatic Expansion
mass of hot rock rising convectively from deep within earth cools off and expands.
Convection
Driven mainly by subduction of cool, dense oceanic lithosphere sinking beneath edge of adjacent plate. Gravity then pulls into asthenosphere. Marked by deep ocean trench.
Global Positioning System (GPS)
Proves: 1) points on earth’s surface drift at slow, steady rate. 2) Plate interiors are rigid
Plate Boundaries/Margins
1) Divergent Margin (Type I)
2) Convergent Margin/Subduction Zone (Type II)
3) Convergent Margin/Collision Zone (Type III)
4) Transform Fault Margin (Type IV)
Strike-slip faults
Known as transform faults when coincide with plate boundary; motion is entirely horizontal
Thrust (and reverse) faults
Accommodate convergent motion between plates; motion is partly horizontal and partly vertical
Normal faults
Accommodate divergent motion; motion also partly horizontal and partly vertical
Divergent Margin (Type I)
Coincides w/mid-ocean ridge; magma forms in asthenosphere, rises to top of lithosphere, and emerges to form new oceanic crust; earthquakes are shallow and small; volcanic activity occurs along fissures; ridges rise 2+km above surrounding sea floor due to thermal expansion and isostasy
Convergent Margin/Subduction Zone (Type II)
Subduction zone marked by volcanic island arc if overriding plate is oceanic, continental volcanic arc if continental; largest/ deepest earthquakes; Benioff zone extends up to 670 km
Convergent Margin/Collision Zone (Type III)
Light, thick continental crust clogs subduction zone after oceanic portion of one plate has been completely subducted; continental plates crumple together to form collision zone; creates a mountain range
Transform Fault Margin (Type IV)
Plates grind past each other horizontally along strike-slip faults; most link mid-ocean ridge segments
Ridge push
Gravity induces lithosphere to slide down gentle slopes of mid-ocean ridge
Slab pull
Cool, dense oceanic lithosphere sinks beneath edge of adjacent plate at subduction zones; gravity then pulls into asthenosphere at ocean trench
Friction
Slab friction drags top, bottom and leading edge of descending lithosphere into subduction zone; plate friction drags elsewhere at base of plate
