Transcript Plate Tectonics

• Chapter 8, Section 2 Objectives:
1. Summarize the theory of plate
tectonics.
2. Compare the characteristic geologic
activities that occur along the three
types of plate boundaries.
3. Explain the possible role of convection
currents in plate movement.
• Theory of Plate Tectonics: describes
continental movement and proposes a
possible explanation of why and how
continents move.
– From Greek word tektonikos, meaning
construction
– Tectonics: the study of the formation of
features in the Earth’s crust
– Earth’s surface consists of a number of
rigid, but moving pieces called plates
2 Types of Earth’s crust
• Oceanic Crust: material on the ocean
floor.
• Continental Crust: makes up the
continental landmasses.
• Lithosphere: made up of the crust
and the rigid upper mantle.
– Forms the thin outer shell of the Earth
– Rigid but broken into plates that move
with respect to one another
• Asthenosphere: a layer of plastic
rock
– Solid rock that slowly flows (like putty)
– Layer within the mantle that the
lithospheric plates rest on
• According to the Theory of Plate
Tectonics:
– Lithosphere is broken into separate
plates
– Plates ride on denser asthenosphere
– Most plates composed of both continental
and oceanic crust
– To date about 30 lithospheric plates have
been identified
• Plate Boundaries:
– Place where one plate is moving
relative to another plate
– 3 types
• Each associated with a characteristic
type of geological activity
• Differs according to the way the plates
move in relation to each other
Kinds of Plate
Boundaries…
• Transform Fault Boundries: plates
are grinding past one another
– Move in a series of sudden spurts of
activity
• Earthquakes
– Ex: San Andreas fault
Example:
San
Andreas
Fault
• Divergent boundaries: where two
lithospheric plates are moving apart
(spreading centers)
- As plates move apart, molten rock rises
and fills space between plates
- cools and hardens creating new oceanic
crust
- Most divergent boundaries are found on
the ocean floor
Mid-Atlantic
Ridge
Spreading
Center
New ocean
floor is
being
created
• Rift Valley: narrow valley formed
as the plates separate.
• Convergent Boundary: the place
where one plate directly collides with
another plate.
– 3 types of convergent boundries
• Oceanic crust collides with
continental crust: since oceanic crust
is denser it is forced under the
continental crust (subducted)
– Subduction Zone: region along a plate
boundary where one plate moves under
another
• Deep Ocean Trench: usually forms
along a subduction zone.
– Oceanic crust moves down
• Melts and becomes part of the mantle material
– Some magma rises through the continental
crust
• Produces volcanic mountains
• Continental crust collides with
continental crust: neither plate is
subducted
– Colliding edges are crumpled and uplifted
– Produces large mountain ranges
• Himalayas
• Oceanic crust collides with oceanic
crust
• Island Arc is formed when:
– One plate is subducted, forming a trench
– Subducted plate melts
– Molten rock rises to surface along trench
• Forms volcanic islands
• Convection: the transfer of heat
through the movement of heated fluid
material.
• Convection Current: the cycle of warm
less dense material rising and cooler
denser material sinking
Let’s go to this website and review!
CLICK HERE>>>
http://www.pbs.org/wgbh/aso/tryit/tectonics/#
Click on Plate Tectonics Activity (with a yellow arrow)
when you get there!
Here it is – all in one big picture…
Can you pick out the types
of Plate Boundaries?
Were you right?