what happens at tectonic plate boundaries?. essential questions what are the 3 types of plate...
TRANSCRIPT
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
http://learning.aliant.net/Player/ALC_Player.asp?ProgID=INT_ENDVOY06
Complete the self test after the video 27mins
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