Three Types of Plate Boundaries

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Three Types of Plate Boundaries
9.3 Actions at Plate Boundaries
Divergent Boundary
Transform Fault Boundary
Convergent Boundary
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9.3 Actions at Plate Boundaries
? Oceanic Ridges and Seafloor Spreading
Oceanic ridges are continuous elevated zones
on the floor of all major ocean basins created at
divergent boundaries. The system of ocean ridges
is the longest physical feature on the Earths
surface stretching more than 70,000 km in length.
Rift valleys are deep faulted structures found
along the axes of divergent plate boundaries.
They can develop on the seafloor or on land.
Seafloor spreading is a process by which plate
tectonics produces new oceanic crust (a.k.a.
lithosphere.)
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Spreading Center

• Typical rates of spreading ridges are 5cm per
  year.
• While this may be considered to be slow in terms
  of our human time it has recycled the ocean
  floor completely in just the last 180 million
  years!

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9.3 Actions at Plate Boundaries
? Continental Rifts
When spreading centers develop within a
continent, the landmass may split into two or
more smaller segments, forming a rift. (A RIFT IS
LIKE A BIG RIP)
East African Rift Valley
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East African Rift Valley
The African continent is splitting apart!
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9.3 Actions at Plate Boundaries
? Oceanic vs. Continental
? Oceanic vs. Oceanic
? Continental vs. Continental
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9.3 Actions at Plate Boundaries
? A subduction zone occurs when one oceanic plate
is forced down into the mantle beneath a second
plate. (LIKE A WAR AMONG PLATES, ONE MUST WIN AND
ONE MUST LOSE)
? Oceanic-Continental
Denser oceanic slab sinks into the
asthenosphere.
Pockets of magma develop and rise.
Continental volcanic arcs form in part by
volcanic activity caused by the subduction of
oceanic lithosphere beneath a continent.
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Oceanic Continental Convergent Boundaries

• Examples include the Andes Mountains, Cascade
  Mountains, and the Sierra Nevada Mountains.

Andes Mountains
Sierra Nevada Mountains
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Oceanic-Continental Convergent Boundary
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9.3 Actions at Plate Boundaries
? Oceanic-Oceanic
Two oceanic slabs converge and one descends
beneath the other.
This kind of boundary often forms volcanoes on
the ocean floor.
Volcanic island arcs form as volcanoes emerge
from the sea.
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Oceanic Oceanic Convergent Boundaries

• Examples include the Aleutian Island Arc,
  Marianas Trench, and Tonga Islands.

Andes Mountains
Tonga Islands
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Oceanic-Oceanic Convergent Boundary
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9.3 Actions at Plate Boundaries
? Continental-Continental
When converging plates contain continental
material, they collide forming this type of
boundary.
This kind of boundary can produce new
mountain ranges, such as the Himalayan Mountain
Range.
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Continental-Continental Convergent Boundary
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The Himalayas!
The Himalayas include the highest mountains on
the surface of the Earth. These mountains were
formed when the leading edge of the Indian plate
was forced partially under the continent Asia
which generated an unusually great thickness of
the continental lithosphere. This thick
accumulation accounts in part for the high
elevation of the Himalayas and may also explain
the elevated Tibetan Plateau to the north.
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Collision of India and Asia
Use p 263 in your book to complete the captions
under the pictures.
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9.3 Actions at Plate Boundaries
? At a transform fault boundary, plates grind
past each other without destroying the
lithosphere.
? Transform faults
Most join two segments of a mid-ocean ridge
because most of these boundaries are located
beneath the ocean.
At the time of formation, they roughly
parallel the direction of plate movement.
They aid the movement of oceanic crustal
material which occurs at spreading ridges.
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Transform Fault Boundary
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Transform Fault Boundary
Although most transform faults are located within
ocean basins, a few cut through continental
crust. One of the most famous examples is the
San Andreas with is a fault between the Pacific
plate and the North American plate. If this
keeps it up, part of California that is west of
the crack adjacent to the Pacific plate with
become its own island!
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Transform Fault Boundary
San Andreas Fault