Transcript Stop the Continent, I Want to Get Off! - PLC-METS

Living on the Edge
Plate Tectonics 2
Convection in the mantle
drives the plate motion
3 Types of Plate Boundaries
• A) Divergent = moving away from
each other
• B) Transform = sliding past each
other
• C) Convergent = moving toward each
other
A) Divergent plate boundaries
• Continental plates break, move apart
New oceanic crust forms at MOR
B) Transform Boundaries
• Plates move past each other
• San Andreas fault
Most transform boundaries are parts of MORs
Displacement along Transform
Boundaries
C)Convergent Plate Boundaries
• Plates collide
• This is where MOST of the world’s
earthquake and volcanic activity
occurs
• “Pacific Ring of Fire”
Three Types of Convergent Boundaries
• 1) Oceanic-Oceanic
• 2) Oceanic-Continental
• 3) Continental-Continental
1) Oceanic – Oceanic Convergence
• As the oceanic crust moves further from the
MOR, it increases in density because of the
weight of water and overlying sediments.
• Therefore, the older the Oceanic crust is – the
more dense it is.
When the edges of two oceanic crustal plates
converge:
• The more dense plate will subduct.
• As the subducting plate moves into the mantle, it heats
and melts.
• Melting decreases the density, so it rises, forming a row of
volcanoes in the ocean parallel to the convergent
boundary.
• This chain of volcanoes is known as a “Volcanic Island
Arc”.
Japan is the classic example:
Mt. Fuji
2) Oceanic-Continental Convergence
• Oceanic Crust is more dense than Continental
Crust because:
• Many of the minerals in Oceanic Crust are
inherently more dense.
• Erosion, weathering, and other surficial processes
leave pore space (filled with gasses or fluids) in the
rocks, decreasing their density.
When an oceanic plate converges with a
continental plate:
• The more dense plate (oceanic) will subduct.
• As the subducting plate moves into the mantle, it heats
and melts.
• Melting decreases the density, so it rises, forming a row of
volcanic mountains parallel to the convergent boundary,
therefore parallel to the continental coast.
• This chain of volcanoes is known as a “Volcanic Arc”.
Classic Examples are the Cascades and the
Andes:
Mt. St. Helens
3) Continental -Continental Convergence
• Both crusts are low-density, so neither will
automatically subduct.
• The two continents will crash together, crumpling
both edges in the process.
• This forms a non-volcanic mountain range at the
convergence, and intense heat and pressure cause
metamorphism in the rocks.
The Himalayas are the classic example:
The Appalachians are another example
The Rock Cycle
So that raps up Plate Tectonics
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