Download plate tectonics - Madison County Schools

Bellringer
Which ocean is getting smaller and which ocean is
getting bigger due to subduction and sea floor
spreading?
Plate Tectonic Theory
Notes
How Plates Move
• Earth’s crust is broken into many
jagged pieces. The surface is like the
shell of a hard-boiled egg that has been
rolled. The pieces of Earth’s crust are
called plates. Plates carry continents,
oceans floors, or both.
How Plates Move
• The theory of plate tectonics says that
Earth’s plates move because of
convection currents in the mantle.
Currents in the mantle carry plates on
Earth’s surface, like currents in water
carry boats on a river, or Cheerios in
milk.
How Plates Move
• Plates can meet in three different ways.
Plates may pull apart, push together, or
slide past each other. Wherever plates
meet, you usually get volcanoes,
mountain ranges, or ocean trenches.
Plate Boundaries
• A plate boundary is where two plates
meet. Faults form along plate
boundaries. A fault is a break in Earth’s
crust where blocks of rock have slipped
past each other.
Plate Boundaries
• Where two plates move apart, the boundary is
called a divergent boundary.
• A divergent boundary between two oceanic
plates will result in a mid-ocean ridge AND rift
valley. (SEE: Sea-Floor Spreading)
• A divergent boundary between two continental
plates will result in only a rift valley.
This is currently
happening at the Great
Rift Valley in east Africa.
Eventually, the Indian
Ocean will pour into the
lowered valley and a new
ocean will form.
•
•
•
•
Plate Boundaries
Where two plates push together, the boundary is called a
convergent boundary.
A convergent boundary between two oceanic plates will result
in an ocean trench, when the more dense (older rock) subducts
beneath the younger, less dense oceanic crust it collides into. It
will also form an island arc as the crust melts and rises up as
magma. (Japan)
A convergent boundary between two continental plates will
result in a mountain range. (Himalayas)
A convergent boundary between one oceanic plate and one
continental plate will result in a trench when the more dense
oceanic crust subducts beneath the continental granite, as well
as a volcanic mountain range as the oceanic crust melts and
rises as magma. (Andes)
Oceanic-Oceanic Convergent Plate Boundary
Continental-Continental Convergent Plate Boundary
Oceanic-Continental Convergent Plate Boundary
Plate Boundaries
• Where two plates slide past each other
in opposite directions, with neither plate
subducting or rising, this forms a
transform boundary. Transform
boundaries typically don’t create
landforms, but they do create numbers
earthquakes. (San Andreas Fault)