http://science.nationalgeographic.com/science/earth/the-dynamic-earth/plate-tectonics-article.html
Plate Tectonics
Sec 3 IHE GE 2014/Chan ML
Convection CurrentsRising, spreading convection currents = pull plates apartSinking convection currents = drag plates together
Why doPlatesMove?
Divergent Plates(Constructive Boundaries)
Cause:Plates move in opposite direction due to
the convection movement.
Effects/Landforms• new crust is created (oceanic ridges) • Oceans are born and grow wider • When a diverging boundary occurs on
land a 'rift', or separation will arise and over time that mass of land will break apart into distinct land masses and the surrounding water will fill the space between them.
• Earthquakes• Volcanoes
http://www.platetectonics.com/book/images/Divergent1.gif
Oceanic-Oceanic
The divergent Mid-Atlantic Ridge rises above sea level at Thingvellir, with the North American plate to the west and the Eurasian plate to
the east.
Formation of Oceanic Ridge (answer)
• As the N. American and Eurasian plates move apart (divergent movement) in a constructive boundary due to convection currents
• Tensional stresses cause fractures in the lithosphere to occur• The zone where the plates separate is the spreading centre,• Allowing basaltic magma to well up, cool and solidify; thus becoming
/ forming new sea floor (this process is called sea floor spreading)• As the plates continue to move apart, more basaltic magma piles
up, cool and solidify; and new mountains are formed • The mountains closest to the spreading zone are the youngest• The rows of mountains rise from 2,000 to 4,000m from the ocean
floor – these are the mid-oceanic ridges• Eg: Mid-Atlantic Ridge
Continental-Continental• As the Nubian and Somalian plates move
apart,• They are stretched and fractures are created• The land in between sinks, creating a linear
depression, known as a rift valley• As a result, earthquakes are experienced in
the region• Magma may also rise to the surface creating
volcanoes• Eg: the East African Rift Valley
Convergent Plates(Destructive Boundaries)
3 types:• Oceanic – oceanic• Oceanic – continent• Continent - continent
http://www.scienceclarified.com/images/uesc_08_img0459.jpg
Oceanic-Oceanic
The Japanese Islands are examples of volcanic island arcs formed by the convergence of two oceanic plates.http://www.lee.edu/~cguldenzopf/Images/Historical/Historicalmw45.jpg
Cause:• 2 oceanic plates collide• One plate sinks beneath the other• Subduction zone
Effects/Landforms:• Trench• Volcanoes• Earthquake
Formation of Trench and volcanoes(answer)
Trench in a convergence between Oceanic and Continental Plate (destructive boundary)• When a thinner and denser oceanic plate converges with
a thicker and lighter continental plate• The oceanic plate descends beneath the continental• This descent is called subduction• The old oceanic lithosphere is destroyed and as it dives
to the mantle, it contributes to the formation of more magma
• A long narrow and deep oceanic trench is formed where the plate dips into the mantle
• Eg: Peru-Chile Trench, Java Trench
Name of plates
• The movement of the plates cause faults to occur
• Rocks break and are displaced relative to each other,
• the melting of the subducting oceanic plate produces silica-rich magma
• Being less dense than the mantle, the magma moves up any break or fractures
• When it escapes through vents to the land surface, it forms subduction volcanoes
• Eg: Mt. St. Helens, Mt Pinatubo
Oceanic-ContinentalCause:• Oceanic plate collides with thinner & lighter
continental plate• Subduction occurs
Effects/Landforms• Descending plate is destroyed• Trenches are formed• Volcanoes• Earthquakes
http://www.revisionworld.com/files/oceaniccont.jpg
Formation of Fold Mountains(answer)
• When two continental masses collide, one is pushed under the other for a short distance
• When a thinner and denser oceanic plate converges with a thicker and lighter continental plate
• The oceanic plate descends beneath the continental• This descent is called subduction• The old oceanic lithosphere is destroyed and as it dives to the
mantle, it contributes to the formation of more magma• The edges of these plates are also contorted and buckled up,
creating a great uplift, forming fold mountains• Since sediments from the ocean floor are contorted and uplifted,
marine fossils were found at the summit of fold mountains!!!• Eg: Rocky Mountains (N. America), Andes Mountains (South
America)
Name of plates
Continental-ContinentalCause:• 2 continental plates collide• No subduction
Effects/Landforms• Great uplift• Rocks are contorted• Earthquakes
Earthquakes are shown as yellow squares.
http://www.visionlearning.com/library/module_viewer.php?mid=66
Formation of Fold Mountains(answer)
• When two continental masses collide, the Indian plate is pushed under the Eurasian plate for a short distance
• However, there is NO subduction• Because both are light and buoyant• This process produces a great uplift as the rocks at the
edges of these two plates are contorted and buckled up• Due to the absence of magma supply, there are no
volcanoes in this area• Eg: the Himalayan Mountains
Transform Boundaries• occur in a few places to accommodate lateral
motion, in which plates slide past one another. • very rare on continents, but they are dramatic
where they do occur. Example: the San Andreas Fault (USA) and The Alpine Fault (New Zealand).
• Most transform boundaries occur in short segments along mid-oceanic ridges
http://www.visionlearning.com/library/module_viewer.php?mid=66
https://www.youtube.com/watch?v=0mWQs1_L3fA
Sit back and relax… well… can’t be too relaxed…Here’s a summary… don’t fall asleep
References
• Chong, Marianne (2001) Aspects of Physical Geography
• Waugh, David (2009) Geography: An Integrated approach