Transcript PPT - Chapter 2: Plate Tectonics & The Ocean Floor

Types of Plate Boundaries
• Divergent Plate Boundaries
• Convergent Plate Boundaries
• Transform Faults
Divergent Plate Boundaries  
• Mid-ocean ridges form along divergent boundaries.
• Magma pushes continental crust up causing it to
break apart.
• Plates begin to move apart in opposite directions
causing crustal material to slump downward,
creating a rift valley.
See animation.. Click here!!
Divergent Plate Boundaries  
• A linear sea is formed as water fills in the valley.
• Through continued divergence, an ocean basin
forms, creating an ocean. Ex: Red Sea
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Red Sea
Divergent Plate Boundaries

• Mid-ocean ridges have oceanic rises and
oceanic ridges.
– Oceanic rises  gently sloping due to a
fast rate of spreading. Ex: East Pacific
Rise
East Pacific Rise
Divergent Plate Boundaries

– Oceanic ridges  have steeper slopes
due to a slower rate of spreading.
Ex: Mid-Atlantic Ridge
Iceland and Mid-ocean Ridge
Convergent Plate Boundaries

• Plates are pushed
together
• Oceanic crust is
subducted and
absorbed into the
mantle creating a
subduction zone
• Produces a deepocean trench and
volcanic arc.
Three types of Convergence
• Oceanic/ Continental (Fig 1)
• Creates a subduction zone
• Subduction creates a deep trench
• On the continental plate, a continental
arc forms parallel to the trench.
Ex: Cascade & Andes Mountains
The Andes
Cascade Mountains
Three types of convergence
• Oceanic/ Oceanic (Fig 2)
– Subduction creates a deep trench.
– As one oceanic plate subducts, a chain of
volcanic mountains form, producing an island
arc. Ex: Aleutian Islands & Mariana Trench
Aleutian Island Arc
Marianas Trench
Three types of convergence
• Continental/ Continental (Fig 3)
– As two continental plates collide, they buckle,
fold and push upward to produce a mountain
range. Ex: Himalayas
Transform Faults/Boundaries
• Plates slide past one
another along faults in the
lithospheric plate
• Crustal material is neither
created nor destroyed
Ex: San Andreas Fault
San Andreas Fault
Hot Spots & Mantle Plumes
• Hot spots are areas of continued volcanic
activity NOT associated with plate
boundaries. Ex: Hawaiian Islands &
Yellowstone National Park
• Hot spots are fueled by regions of rising
molten rock called mantle plumes.
(pg 62)
• Super volcano?????
• Old Faithful
Convection Cells and Magma Plumes
Seamounts & Tablemounts
• Underwater volcanoes are called seamounts.
• As seamounts break the surface of the ocean,
they may become islands.
• Over time, the seamount’s peak erodes away
as the seamount subsides, eventually
becoming a flat-top tablemount or Guyot.
Hawaiian-Emperor Seamount
Coral Reef Formation
• Fringing Reef: grow close to land, associated
with active volcanic islands. Ex: Kurumba
Island in the Maldives
Coral Reef Formation
• Barrier Reef: Linear or circular reefs
separated from land by a lagoon of water.
Ex: Great Barrier Reef
Coral Reef Formation
• Atoll: By this stage, the volcano is completely
submerged. All that remains is the reef and
a lagoon. Ex: Atafu in S. Pacific
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The Big Picture
1-Asthenosphere
2-Lithosphere
3-Hot spot
4-Oceanic crust
5-Subducting plate
6-Continental crust
7-Continental rift zone (young
plate boundary)
8-Convergent boundary plate
9-Divergent boundary plate
10-Transform plate boundary
11-Shield volcano
12-Oceanic spreading ridge
13-Convergent plate boundary
14-Strato volcano
15-Island arc
16-Plate
17-Asthenosphere
18-Trench
And finally . . .