Chapter 7Chapter 7

Plate Tectonics

Chap 7, Sec 3 (The Theory of Plate Tectonics)

What we will learn:

1. Describe the 3 types of plate boundaries.

2. Explain the difference between the 3 types of faults.

3. Describe the 3 types of stress that deform rock.

Vocab:1. plates – separate sections of the

lithosphere.

2. plate tectonics –theory that states that pieces of lithosphere are in constant motion, driven by convection currents in the mantle.

3. faults – breaks in Earth’s crust where plate boundaries form.

4. transform boundary – a place where two plates slide past each other in opposite directions (earthquakes are frequent).

5. divergent boundary – the place where two plates move apart, or dive away (most occur at the mid-ocean ridge).

6. rift valley – develops on land, where two plates diverge.

Mid Ocean RidgeMid Ocean Ridge

7. convergent boundary – the place where two plates come together, or collide. (the density of the plates dictates which one comes out on top).

Ex: at the deep ocean trench where the oceanic crust (basalt) is more dense than the continental crust (granite)

which is less dense

SubductionSubduction

Types of StressTypes of Stress

• Deformation: Process that changes the shape of rock because of stress.

• Tension: stress that forms when forces act to stretch an object (rubber band)

• Compression: stress that forms when forces squeeze an the rock.

• Shearing: pushes mass of rock in 2 opposite direction.

FaultsFaults

• Surface where rocks break or slide past each other.

• Hanging wall: the wall you would han g from.

• Footwall: the wall you put your foot on.

FaultsFaults

• Normal Fault: Rocks are pulled apart; hanging wall moves down relative to the footwall.

• Reverse Fault: rocks are pushed together by compression, hanging wall moves up relative to footwall

FaultsFaults

• Strike-slip Fault: rocks are moved horizontally by opposite directions.

Mountain BuildingMountain Building

• Folded Mountains: form where continents have collided.

• Applachians: formed when North America and Africa collided.

Hint: push on the edges of a piece of paper towards the center.

Mountain BuildingMountain Building

• Fault-block mountains: form when tension from normal faults forces blocks of rock to move upward