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…

Imagine Rice boiling, what path of motion is the rice moving in?

It is moving 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

Why does the rice move in circles?

Boiling Water

Convection CurrentsConvection Currents are the

movement of magma in the asthenosphere in circles. (like the rice)

They move around the floating tectonic plates above them

AnimationAnimation

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:

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.

Draw arrows to show direction of stress

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?

FaultsA 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

FaultsFaults

Part III. Part III. Convergent Convergent Plate Plate BoundariesBoundaries

Earthquake Map

I. Plate TectonicsI. Plate TectonicsA. Plate Tectonics Theory states that the lithosphere is broken up into 8 major plates that move relative to one another.

I. Plate TectonicsI. Plate TectonicsB. Much of Earth’s mountain building, earthquakes, and volcanoes occur at boundaries between plates.

II. Plate Boundaries II. Plate Boundaries (Borderlines between (Borderlines between plates)plates)A. Convergent Plate Boundaries1. 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 III. Convergent Plate BoundariesBoundariesA. Continental-Continental Boundary1. 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

CheckpointUsing your arms as plates, be ready to show what happens when two continental plates collide.

Go!

III. Convergent Plate III. Convergent Plate BoundariesBoundariesB. Oceanic-Continental Boundary1. 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 III. Convergent Plate BoundariesBoundaries2. This is called a Subduction Zone.◦When the more dense oceanic plate goes under (subducts) the less dense continental crust.

IV. Environmental IV. Environmental Characteristics of a Characteristics of a Subduction ZoneSubduction ZoneA. EARTHQUAKES occur when plates grind against one another.

IV. Environmental IV. Environmental Characteristics of a Characteristics of a Subduction ZoneSubduction ZoneB. VOLCANOES form when magma rises back through the crust.

IV. Environmental IV. Environmental Characteristics of a Characteristics of a Subduction ZoneSubduction ZoneC. Trenches or large canyons form in the ocean.

Lets find some convergent plate boundaries using the ESRT pg. 5

Assessment

Question #1What are the plates at a

convergent boundary doing?1. Moving Apart2. Moving Together3. Sliding Past Each Other4. Staying Still

Assessment

Question #2

Which plate will float atop the other at a Continental-Oceanic Crust Convergent Boundary?

1. Continental Crust

2. Oceanic Crust

3. Asthenosphere

4. Lithosphere