Warm-up:

• What are the two types of crust?• What’s the difference?

Plate BoundariesPlate boundaries occur where

two crustal plates meet.There are three types of plate

boundaries:1. Divergent plate boundaries

(constructive margins) occur where two plates move

apart.2. Convergent plate boundaries

(destructive margins) occur where two plates collide.

3. Transform fault boundaries occur where plates slide past

one another

Divergent Plate BoundariesDivergent plate boundaries

(constructive margins) occur where two plates move

apart.

The mantle material up-wells to create new seafloor.

Oceanic ridges develop along well-developed boundaries.

Along ridges, seafloor spreading creates new

seafloor.

Divergent boundaries are located along

oceanic ridges.

Figure 7.11

Distribution of the Oceanic Ridge System

Figure 7.10 (left)

The East African rift is

a divergent

boundary on land

Figure 7.13

Continental rifts form at spreading

centers within a continent.

Figure 7.13 (top right)

Continentalrifting

Convergent Plate BoundariesConvergent plate

boundaries (destructive margins)

occur when plates collide, an ocean trench forms, and

lithosphere is subducted into the

mantle.

Convergent Plate BoundariesOceanic - continental convergence occurs when a denser oceanic slab sinks into the

asthenosphere. Pockets of magma develop and rise and a

continental volcanic arc forms.

An Oceanic - Continental Convergent Plate Boundary

Figure 7.15 A

Convergent Plate BoundariesExamples of oceanic – continental convergence include:the Andes Mountains of South America.

Convergent Plate BoundariesExamples of oceanic – continental convergence include:

the Cascade Mountains of Washington and Oregon.

Convergent Plate BoundariesExamples of oceanic – continental convergence include:

the Sierra Nevada Mountains of California.

Convergent Plate BoundariesOceanic - oceanic convergence occurs when two oceanic slabs converge and one descends beneath the other. This often forms volcanoes on the ocean floor.

A volcanic island arc forms as volcanoes emerge from the sea.

Convergent Plate BoundariesExamples of oceanic – oceanic convergence include:the Aleutian

Islands.

Convergent Plate BoundariesExamples of oceanic – oceanic convergence include:the Mariana Islands.

Convergent Plate BoundariesExamples of oceanic – oceanic convergence include:the Tonga Islands.

Convergent Plate BoundariesContinental - Continental Convergence When two continental plates converge, they collide.

One continental plate subducts under the other.This can produce buckling of the upper plate and new mountain ranges

form, such as the Himalayas

The Collision of India and Asia Produced the Himalayas

Transform Plate BoundariesTransform plates slide past one another.

No new crust is created or destroyed.

Transform faults are created.

Most transform faults join two segments of a

mid-ocean ridge. These faults and ridges aid the movement of

oceanic crustal material.

California’s Fault Issue