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 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: 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?

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.Moving Apart 2.Moving Together 3.Sliding Past Each Other 4.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