Download Aim #9: Plate Tectonics Theory – Convergent

Part II: Convection in
the Mantle
and
Crustal Deformation

Alfred Wegener was
considered a fraud and a
phony is the science
world because he was
missing one important
detail in his work…
What causes the
continents to move?
Here are those moving Tectonic Plates
******ESRT PAGE 5******
Another look at the plates…
Boiling Water
Imagine Rice boiling, what path of
motion is the rice moving in?
It is moving in circles
Why does the rice move in circles?
The water/rice heats and rises
then cools at the surface and
sinks continuing the circle
*CHANGES IN DENSITY
-Hot Rises
-Cool Sinks


Convection Currents
Convection Currents are the movement of
magma in the asthenosphere in circles. (like
the rice)
They move around the floating tectonic
plates above them
Animation
How Convection Works!

Magma expands when heated making
volume larger making magma less dense
therefore it will __________ to the top of
more dense magma
•When the magma reaches the
surface it cools and contracts
becoming _________
_____________ and it will sink.
•The process keeps continuing in
a circle or cyclic cycle.
Sinking
Rising
Example 2: Plates Pulling Apart and
Pushing Together
You don’t have to memorize
Circle and Label where the convection
currents are moving plates together and
pulling them apart.
WHAT HAPPENS TO THE CRUST
WHEN THE PLATES ARE MOVING
AROUND????
What things do we see at these
places?
Law of Original Horizontality

Rocks are formed in flat horizontal layers
Tilting

When originally flat lying layers of rocks are tilted
at an angle to the ground.
Tilting Continued:
Draw arrows to show direction of stress



This happens when the rock layers are being UPLIFTED or
COMPRESSED TOGETHER
We also assume that the tilting never exceeded 90 degrees.
It is easier to tilt something up slightly, but to tilt it up and flip
it is much harder.
Folding
Folding occurs when layers of rocks are
compressed.
 Think of a sheet of paper, when you push on both
ends at the same time it folds!

Which way are the layers being moved?
Faults
A
fracture in the Earth along
which movement occurs.
 When this movement occurs an
Earthquake is generated.
 There
are 3 types of faults
Normal Faults
Normal faults are the result of pulling forces.
 In a normal fault one side is moved down relative
to the other.

Reverse Faults
Reverse faults are the result of compressional
forces.
 These forces push rock layers on one side UP
and over the opposite side.

Transform Faults
In transform faults the movement is horizontal
(side to side) relative to the fault.
 The San Andreas Fault is a transform fault.

Faults Website
NORMAL FAULT
REVERSE FAULT
TRANSFORM FAULT
Faults
Part III. Convergent
Plate Boundaries
Earthquake Map
I. Plate Tectonics
 A. Plate Tectonics Theory
states that the
lithosphere is broken up into 8 major plates
that move relative to one another.
I. Plate Tectonics

B. Much of Earth’s mountain building,
earthquakes, and volcanoes occur at
boundaries between plates.
II. Plate Boundaries (Borderlines
between plates)
A. Convergent Plate Boundaries
 1. Occur when 2 plates converge, or move
towards one another.

Checkpoint!

Use your hands to demonstrate the
motion at a convergent plate
boundary
Convergent

III. Convergent Plate Boundaries
A. Continental-Continental Boundary
 1. When 2 continents collide, they bunch
up together, because they have
approximately the same density. In other
words, mountains form.


2. The best example of
this occurs where the
Indian-Australian Plate is
colliding with the
Eurasian Plate. This
collision formed the
Himalayas.
◦Mt. Everest
Checkpoint
Using your arms as plates, be ready to show
what happens when two continental plates
collide.
 Go!

III. Convergent Plate Boundaries
B. Oceanic-Continental Boundary
 1. When a continental plate and oceanic
plate converge, the oceanic plate sinks
below because it is more dense.

Checkpoint!
Recall how it gets hotter as you go deeper
into the Earth’s interior…
 Visualize what will happen to an oceanic
plate as it sinks further and further below
continental crust…
 Discuss what will happen to that oceanic
plate.

III. Convergent Plate Boundaries

2. This is called a Subduction Zone.
◦ When the more dense oceanic plate goes
under (subducts) the less dense continental
crust.
IV. Environmental Characteristics of a
Subduction Zone

A. EARTHQUAKES occur when plates
grind against one another.
IV. Environmental Characteristics of a
Subduction Zone

B.VOLCANOES form when magma rises
back through the crust.
IV. Environmental Characteristics of a
Subduction Zone

C. Trenches or large canyons form in the
ocean.
Lets find some convergent plate boundaries using the ESRT pg. 5
Assessment
Question #1
What are the plates at a convergent
boundary doing?
1.
2.
3.
4.
Moving Apart
Moving Together
Sliding Past Each Other
Staying Still
Assessment
Question #2
Which plate will float atop the other at a
Continental-Oceanic Crust Convergent
Boundary?
1.
2.
3.
4.
Continental Crust
Oceanic Crust
Asthenosphere
Lithosphere