TuesdayNovember 2, 2010

(Types of Plate Boundaries)

The Launch PadTuesday, 11/2/10

In 1915, Alfred Wegener first proposed the continental drift hypothesis, which states that a supercontinent called Pangaea began breaking

apart about 200 million years ago. He said that the continents “drifted” to their present positions.List 5 pieces of evidence cited by Wegener that

supported his hypothesis.the fit of South America and Africa

fossils match across the seasrock types and structures match across the

seassimilar mountain ranges on different continentssimilar ancient climates evidence matches

on present-day continents

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Plate 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

Plate Boundaries

Divergent 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 Plate Boundaries

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 boundaries

(destructive margins) occur when plates collide, an ocean trench forms, and

lithosphere is subducted into the

mantle.

Convergent Plate Boundaries

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.

Oceanic - 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 Boundaries

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.

Continental - 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

Convergent Plate Boundaries

The Collision of India and Asia Produced the Himalayas

Transform 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.

Transform Plate Boundaries

California’s Fault Issue

GEODe Earth Science

Plate TectonicsSlides 726-754 (P5)