Transcript What happens at tectonic plate boundaries?

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
Three types of plate boundary
 Divergent
 Convergent
 Transform
World in Motion
The Endless Voyage Series
 http://learning.aliant.net/Player/ALC_
Player.asp?ProgID=INT_ENDVOY06
 Complete the self test after the video
 27mins
Divergent Boundaries
 Spreading ridges
 As plates move apart new material is erupted
to fill the gap
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:
An example of continental rifting
 Iceland has a divergent
plate boundary running
through its middle
Convergent Boundaries
 There are three styles of convergent
plate boundaries
 Continent-continent collision
 Continent-oceanic crust collision
 Ocean-ocean collision
Continent-Continent Collision
 When two continental plates collide
 The crust crumples and thickens,
creating high mountains and a wide
plateau
 Forms mountains, e.g. European Alps,
Himalayas
Himalayas
Continent-Oceanic Crust Collision
 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
Subduction
 Oceanic lithosphere
subducts underneath the
continental lithosphere
 Oceanic lithosphere heats
and dehydrates as it
subsides
 The melt rises forming
volcanism
 E.g. The Andes
Ocean-Ocean Plate Collision
 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!
Transform Boundaries
 Where plates slide past each
other
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