Chapter 7 Plate Tectonics
Section 3: The Theory of Plate Tectonics
I. Plate Tectonics
A. What is plate tectonics? The theory that the Earth’s lithosphere is
divided into tectonic plates that move around on top of the
asthenosphere.
II. Tectonic Plate Boundaries
A. What are the three types of plate boundaries?
1. What is a convergent boundary? When two tectonic plates
collide
2. What are three types of Convergent Boundaries?
a. Continental – Continental Collisions: when two
continental plates collide, they buckle and thicken, which
pushes the continental crust upward.
b. Continental – Oceanic Collisions: when a plate with
oceanic crust collides with a plate with continental crust,
the denser oceanic crust sinks into the asthenosphere.
c. Oceanic – Oceanic Collisions: when two oceanic plates
collide, one of the oceanic plates is subducted or sinks
under the other plate.
3. What is Subduction? Old ocean crust gets pushed into the
asthenosphere, where it is remelted and recycled.
4. What is a divergent boundary? When two tectonic plates
separate
5. What is the most common type of divergent boundary? midocean ridges
6. What is a transform boundary? when two tectonic plates slide
past each other horizontally
7. What is an example of a transform boundary? the San
Andreas fault in California where the Pacific plate and North
American Plate are sliding past each other.
III. Possible Causes of Tectonic Plate Motion
A. Convection: hot rock from deep within the Earth rises, but cooler
rock near the surface sinks, causing the oceanic lithosphere to move
sideways and away from the mid-ocean ridge
IV. Tracking Tectonic Plate Motion
A. How do scientists track plate movement? GPS to track the
movement of the plates
Chapter 7 Plate Tectonics
Section 4 Deforming the Earth’s Crust
I. Deformation
A. Stress: the amount of force per unit area on a given material.
B. Deformation: the process by which the shape of a rock changes
because of stress.
C. Compression: the type of stress that occurs when an object is
squeezed, such as when two tectonic plates collide. It occurs at a
convergent boundary.
D. Tension: stress that occurs when forces act to stretch an object.
They occur at divergent boundaries such as mid-ocean ridges.
II. Folding
A. Definition: the bending of rock layers because of stress in the
Earth’s crust.
B. Types of Folds
1. Anticlines: upward arching folds
2. Synclines: downward, troughlike folds
3. Monoclines: both ends form horizontal
III. Faulting
A. Definition: the surface along which rocks break and slide past each
other
B. What are the two sides called? Hanging wall and footwall
C. What are the three types of faults?
1. Normal Fault: the hanging wall moves down relative to the
footwall. This is caused by tension.
2. Reverse Fault: the hanging wall moves up relative to the
footwall. This is caused by compression.
3. Strike-Slip Fault: form when opposing forces cause rock to
break and move horizontally.
IV. Plate Tectonics and Mountain Building
A. Folded Mountains: form when rock layers are squeezed together
and pushed upward. They form at convergent boundaries.
B. Fault-Block Mountains: form when this tension causes large blocks
of the Earth’s crust to drop down relative to other blocks.
C. Volcanic Mountains: the rock that is melted in Subduction zones
forms magma, which rises to Earth’s Surface and erupts to form
volcanic mountains.