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					Plate Tectonics:
 Plate Dynamics




                   Dr. R. B. Schultz
     The Dynamics of Plate
          Tectonics


Here, we will learn
HOW and WHY
plates move and
what happens when
they collide or pull
apart from each
other.
                        Do you know how each
                        of these mountain
                        chains were formed?




Plate tectonics
supplies the answers!
The theory of plate tectonics is that rigid lithospheric plates move
across the surface of the earth. There are approximately 12 major and
8 minor plates that move in concert with each other.
Some pull apart, some push together and some move horizontally
against each other.
The plate motion is driven by one or more of the following mechanisms:
 1. Convection -- heat transferred by movement of a fluid (magma)
 2. Conduction -- heat transfer by touching plates
 3. Push-Pull Slab -- heavy slabs pull plates downward and magma forced
    upward pushes plates to the surface (upwelling)
 There are several geological processes that occur where plates meet
(called plate boundaries or margins):
 1.    Volcanoes tend to erupt at plate margins as a result of a process
       called subduction
 2.    Earthquakes occur where plates grind against or over one other
 3.    Mountain building occurs as one plate is pushed over another
 4.    Seafloor spreading occurs where two oceanic plates pull apart
There are three (3) major types of plate boundaries (margins):
 1.     Convergent -- plates move towards each other (compression)
 2.    Divergent -- plates move away from each other (tension)
 3.    Transform -- plates horizontally grind against one another (strike-slip
      motion)
How do the plates move?
Types of Plate Boundaries:


Divergent




Convergent




Transform
Oceanic spreading center with convection of
magma occurring in the mantle.
Convection Cell Development in Mantle




                 A. Volcanic Arc
B. Oceanic Rift Zone         C. Transform Fault Zone
Volcanic Zones Depicting Plate Boundaries
Earthquake Zones in Relation to Plate Boundaries
Subducting Plate
“Hot Spot” Volcanism
Plate boundaries can occur on landmasses (continents) or in marine settings (oceans)
or both at the same time.

Convergent plate movement is associated with the following:
    a.   Compression
    b.   Reverse faulting
    c.   Creation of a subduction zone
    d.   Mountain building processes
    e.   Collisions of plates:
    •    1. Continent vs. continent
    •    2. Continent vs. oceanic
    •    3. Oceanic vs. oceanic


Divergent plate boundaries are associated with the following:
    a.    Tension or extension (pulling apart)
    b.    Normal faulting
    c.    Rifting (as in the mid-oceanic rift zone)
    d.    Creation of magma material inside the rift zone


Transform boundaries are associated with the following:
    a.   Horizontal grinding motion
    b.   Strike-slip faulting
    c.   Lateral offset of rock units
Collision Zones:


Continent vs. Oceanic




Oceanic vs. Oceanic




Continental vs. Continental
Continent vs. Oceanic Collision Zone
Example of Continent vs. Continent Collision Zone: India vs. Asia
Volcanic Zones (both continental and oceanic in origin) associated with Plate Tectonics
are located:

Subduction zones
   •   A. Continent vs. ocean collision (ex.: Andes Mts., Pacific NW of U.S
   •   B. Ocean vs. ocean collision (ex.: Japan, Philippines); Basaltic rocks

Rift Zones (Spreading centers) are located:
     •  A. Ocean - ocean divergent zones (ex.: mid-oceanic rift); Basaltic rocks
     •  B. Continental rift zone (ex.: East African Rift Zone); Granitic rocks

"Hot Spot" Volcanism is located:
    •   A. Oceanic; (ex.: Hawaiian Islands chain); Basaltic rocks
    •   B. Continental; (ex.: Yellowstone Nat. Park); Granitic/Andesitic rocks

Seismic (Earthquake) Zones associated with Plate Tectonics:
    •   Subducting oceanic plate; shallow focus as plate subducts
    •   Intermediate focus earthquakes; partial melting and rising of magma; in the
        "Benioff Zone"
    •   Deep focus as slab of crust is pulled by sheer gravity
East African Rift Zone
    Features/Landforms Associated with Plate Tectonics
1. Continent vs. Oceanic collision zone: subduction zone,
   deep sea trench associated, volcanic arc, andesitic
   volcanic rock.

2. Continent vs. Continent collision zone: Granitic rocks,
   mountain building processes, no volcanism, no
   magmatic activities.

3. Oceanic vs. Oceanic collision zone: deep sea trench
                                  zone
   associated, volcanic island arc, basaltic volcanic rock.

4. Divergent zone: Oceanic, basaltic magma, spreading
              zone
   center (Mid-Ocean Ridge). Also, Continental: granitic,
   (East African Rift Zone)
                        Plate Tectonics Summary

Continental vs. Oceanic crust
Continental crust = lighter, thicker, less dense (Al, K, Si), Granitic
Oceanic crust = darker, thinner, denser (Fe, Mg, Ca) Basaltic

Layers of the Earth
Lithosphere/crust = outermost
Mantle houses magma (molten rock)
Outer core is liquid iron and nickel
Inner core is solid iron and nickel

Evolutionary History of Plate Tectonics Development
Alfred Wegener - polar wandering and continental drift (1912-1930)
Harry Hess - seafloor spreading (late 1950's and early 1960's)
Frederick Vine and Drummond Matthews - magnetic polarities, subduction (1960's)
Robert Palmer and Donald McKenzie - synthesizers of previous ideas, named "plate
tectonics"

Plate Dynamics
12-15 major lithospheric plates; includes both oceanic and continental crust
Three types of plate boundaries or margins:
Convergent: compression
Divergent: tension/extension
Transform: strike-slip horizontal motion

Occurrences/activities at plate boundaries
Earthquakes
Volcanoes
Mountain building
Seafloor spreading
       Convergent Plate Boundaries
Continental vs. Oceanic crust: Cascade Mts. (Pacific NW) and Andes Mts. (Western S. America)
Subduction zone with deep sea trench
Volcanic arc with Andesitic volcanoes
Oceanic vs., Oceanic crust
Volcanic island arc with basaltic volcanoes
Deep sea trench with NO subduction zone
Continental vs. Continental crust
Granitic mountains but NO volcanoes
Strong earthquakes as in India vs. Asia collision


      Divergent plate boundaries
Mid-oceanic ridge (rift zone) with basaltic pillow lava volcanoes
East African rift zone with granitic rock


      Transform boundaries
Ridge-ridge faults - in oceanic setting
Strike-slip faults - continental setting (San Andreas Fault in California)


     Earthquakes in convergent zones
Shallow focus near deep sea trench
Intermediate focus where oceanic plate melts (Benioff Zone)
Deep focus - never deeper than 500 miles (700 km) plate completely melted
      Volcanoes
Andesitic - in subduction zones
Basaltic - ocean vs. ocean collision zones and mid-oceanic ridge
"Hot Spot" - Hawaiian Islands chain in ocean setting; Yellowstone National Park
       in continental setting


    Causes for Plate Movement
Convection -cells of magma (lava lamp type movement) - most probable cause
Conduction - transference of heat from one plate to another
Push-pull slab - especially at leading edge of subduction zones and mid-oceanic
ridges


       Miscellaneous
Gondwanaland - S. America, Africa, Antarctica, and Australia bunched at S. Pole
300+ million years ago
Pangaea: "Super continent" that split apart 200 million years ago;
           next "Pangaea" in 250 million years from now
                        Key Terminology
Oceanic crust                      Continental crust
Lithosphere                        Asthenosphere
Mantle                             Magma
Inner Core                         Outer Core
Mohorovicic Discontinuity (Moho)   Polar Wandering
Continental Drift                  Alfred Wegener
Harry Hess                         Seafloor Spreading
Echo Sounding                      Mid-Oceanic Ridge (Rift) Zone
Glomar Challenger                  Magnetic Reversal
Frederick Vine                     Drummond Matthews
Robert Palmer                      Donald MacKenzie
Plate Tectonics                    Convection
Conduction                         Push-Pull Slab
Convergent                         Divergent
Transform                          Plate Boundary (Margin)
Subduction Zone                    Deep Sea Trench
Volcanic Arc                       Volcanic Island Arc
“Hot Spot” Volcanism               Collision Zones
Benioff Zone                       East African Rift Zone
Gondwanaland                       Pangaea

				
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