What happens at tectonic plate boundaries?

Essential Questions

What are the 3 types of plate boundaries?

What happens at each of these types of boundaries?

What are some examples of these plate boundaries?

The Plate Tectonic System

Is energized by Earth’s internal Heat Composed of:

Lithosphere Asthenosphere Deep mantle

This supplies the energy that melts rocks, moves continents, and ligts up mountains

Divergent

Convergent

Transform

Three types of plate boundary

World in MotionThe Endless Voyage Series

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Spreading ridges As plates move apart new material is erupted

to fill the gap

Divergent Boundaries

Types of Divergent Boundaries Oceanic Plate Separation

Rifting and spreading along a narrow zone have created the Mid-Atlantic Rige, a mid-ocean mountain chain where volcanoes and earthquakes are concentrated

Continental Plate Separation In East Africa, rifting and spreading have created

parallel valleys in a zone with volcanoes and earthquakes: Great Rift Valley

Age of Oceanic Crust

Courtesy of www.ngdc.noaa.gov

The Seafloor as a Magnetic Tape Recorder

Magnetometers Developed during WWII to detect subs Towed behind research vessels to

measure the magnetic field of the sea floor Discovered that the intensity of the

magnetic field alternated between high and low values Termed magnetic anomalies

Magnetic Anomalies Almost perfectly symmetrical with respect to the crest

of the md-ocean ridge Are evidence that Earth’s magnetic field does not

remain constant Magnetic reversals occur, flipping the orientation of

the North and South pole When iron rich lavas cool, they become slightly but

permanently magnetized in the direction of Earth’s magnetic field This is thermoremanent magnetization

About half of all rocks studied have been found to be magnetized in a direction opposite to the Earth’s present magnetic field

Each cycle lasts about 1/2million years b

Iceland has a divergent plate boundary running through its middle

Iceland: An example of continental rifting

There are three styles of convergent plate boundaries Continent-continent collision Continent-oceanic crust collision Ocean-ocean collision

Convergent Boundaries

When two continental plates collide The crust crumples and thickens, creating high mountains and

a wide plateau Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

Himalayas

Called SUBDUCTION When oceanic crust meets continental

crust The oceanic plate is subducted, and a

volcanic belt of mountains is formed at the continental plate margin

Ex: Peru-Chile Trench

Continent-Oceanic Crust Collision

Oceanic lithosphere subducts underneath the continental lithosphere

Oceanic lithosphere heats and dehydrates as it subsides

The melt rises forming volcanism

E.g. The Andes

Subduction

When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.

The worlds deepest parts of the ocean are found along trenches. E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

Where plates slide past each other

Transform Boundaries

Above: View of the San Andreas transform fault

Types of Transform-Fault Boundaries

Mid-Ocean Ridge Transform Fault Spreading centers are offset by mid-ocean ridge

transform faults, where the two oceanic plates slide horizontally past each other

Continental Transform Fault Where a continental plate slide past another

plate Ex the San Andreas Fault – where the Pacific

plate slides past the North American plate