Download Plate Tectonics

Plate Tectonics
The Layers of the Earth
The outer shell of the Earth is known as the lithosphere. It makes up the solid, relatively rigid outer shell of
the Earth. It is broken up into pieces called plates (tectonic plates).
These plates are made up of 2 different types of material:
1. oceanic crust (makes up the ocean floor) (denser)
 Rock type: Basalt (a denser, darker-colored rock that is high in iron and magnesium)
2. continental crust (what we live on) (less dense)
 Rock type: Granite (a less-dense, lighter-colored rock made up of feldspar & quartz)
 Some plates are mostly made up of oceanic crust.
 Some plates are mostly made up of continental crust.
 Some plates are made up of partly oceanic and partly continental.
Layers of the Earth:
Inner Core – solid nickel & iron
Outer Core – liquid nickel & iron
The flowing material here creates the
magnetosphere
Mantle
 Lower Mantle – More solid-like
 Upper Mantle – Plastic-like
(plasticity) (asthenosphere)
Lithosphere – Solid, rigid outer shell
(continental & oceanic crust)
These tectonic plates “float” on top of the next layer of the Earth which is called the asthenosphere.
 It is a layer of rock found in the upper part of the mantle.
 It is unique in that it is a solid but it has the ability to flow like a liquid. This is known as plasticity.
What causes this rock to be plastic-like is:
 The intense pressure from the weight of the lithosphere
 The great heat coming up from within the earth
There are 3 types of plate boundaries:
a. Divergent - plates moving apart
b. Transform - plates sliding past one another
c. Convergent - plates coming together
1. Divergent Boundaries: (Two plates moving away from one another)
As the plates move away from one another the pressure
upon the asthenosphere is reduced causing the plastic-like
asthenosphere material to turn into magma and rise into
the gap which is created. This all happens at the rift valley
The lithosphere is made larger as the magma cools and
hardens at the rift valley
2. Trasform Boundaries: The plate interaction where 2 plates “slide” past each other.
The jagged chunks of rock along the edges of the plates will catch, hold energy back and eventually break,
releasing the stored energy resulting in: EARTHQUAKES
3. Convergent Boundaries 2 plates moving toward each other.
Because there are 2 different types of crustal material (oceanic & continental) there can be 3 different types
of collisions that can occur:
 Oceanic crust colliding with Continental crust
 Continental crust colliding with Continental crust
 Oceanic crust colliding with Oceanic crust
Oceanic crust colliding with Continental crust
Oceanic crust is denser, it is subducted (pushed down into the Earth).
The region where this occurs is known as a Subduction Zone.
The subducted plate melts due to:
 heat from the asthenosphere
 friction from the plates grinding over one another
An oceanic plate converges on a continental plate and the
denser crust of the oceanic plate sinks beneath the morebuoyant continental plate. In this type of convergence,
trenches, strong, destructive earthquakes and the rapid
uplift of mountain ranges are common
The magma that results when the oceanic plate melts rises
up through the continental crust and can result in a long
chain of volcanic mountains on the continental crust. This
formation is known as a continental arc.
Continental crust colliding with Continental crust
Both plates have a low density and neither one wants to go into the Earth.
When two continents meet head-on, neither is
subducted because the continental rocks are
relatively light and, resist downward motion.
Instead, the crust tends to buckle and be pushed
upward or sideways.
The colliding edges of the plates are crumpled
(folded) and uplifted. Large mountain ranges
(folded mountains) are produced from this
uplifting.
Oceanic crust colliding with Oceanic crust
One of the Oceanic crusts is subducted (the one that is mostly oceanic is denser).
This results in the formation of a subduction zone and a very deep trench.
The plate melts due to:
 heat from the asthenosphere
 friction from the plates grinding over one another
When two oceanic plates converge, one subducts
beneath the other, and in the process a trench is
formed.
The magma that results when the plate melts rises up
through the other oceanic crust and can result in a long
chain of volcanic islands on the other oceanic crust.
This formation is known as an island arc.