CONTINENTAL DRIFT

1
CONTINENTAL DRIFT

• Proposed by Alfred Wegener in 1912
• Evidence
• Fossils (land animals and tropical plants)
• Rock / mineral formations
• Glacial sediments
• Fit of the continents
• Pangaea
• Couldnt explain cause thus, not accepted until
  years later.

2
SEA FLOOR SPREADING

• Proposed by Harry Hess in 1959
• Evidence
• mid oceanic ridges
• Paleomagnetism - Magnetic stripes equal in width
  and distance on opposite sides of ridges
• Sea floor rocks are youngest at ridges and older
  the further away from the ridges
• Cause still not explained

3
PLATE TECTONICS

• Proposed in 1968
• Lithosphere broken in pieces called plates float
  on asthenosphere - convection in asthenosphere
  causes plate movement
• Plate types (7 major, 6 minor, and dozens of
  small plates)
• Most major plates composed of oceanic and
  continental crust

4
PLATE BOUNDARIES

• Divergent - plates separate
• Convergent - plates collide
• Transform (lateral, strike-slip) fault - plates
  slide past one another

5
DIVERGENT BOUNDARIES

• Mid-ocean ridges
• Mid-Atlantic Ridge system
• Rift zones
• Red Sea
• East Africa

6
CONVERGENT BOUNDARY FEATURES

• Subduction - denser plate (oceanic) pulled
  underneath into the mantle
• Volcanic Arcs (Island and Continental)
• Trenches
• Collision mountains

7
CONVERGENT BOUNDARIES

• 3 types
• Ocean - ocean (Japan, Aleutian Isles., Indonesia,
  Phillippines)
• Ocean - continent (Cascade Mts., Andes Mts.)
• Continent continent (Himalayan Mts.)

8
TRANSFORM FAULT BOUNDARIES

• San Andreas fault
• Mid Ocean ridge offsets (fracture zones)

9
ADDITIONAL PLATE TECTONICS EVIDENCE

• Apparent polar wandering
• Apparent moving hot spots

10
MECHANICS OF PLATE TECTONICS

• Convection in asthenosphere
• Slab pull
• Ridge push
• Slab suction