Transcript Plate Tectonics - Michigan State University

David Crewes
CEP 811
Was Wegener crazy or did we just move a little bit?
Navigation Instructions:
 The following slide show is brought to you by the Earth Science HSCE’s of the
state of Michigan, and will assist each of you in reviewing for the material in
Chapter 17 covering plate tectonics.
 There will first be a brief review of the more important topics, then the quiz that
follows will allow you to gauge your own retention of the class material.
 You will notice several buttons on the bottom of each slide. They look like this:
 These will take you to the previous slide, the next slide, or back to the first slide.
 Some slides won’t have any buttons, but they will have some sort of question.
Pick the correct answer, and you will move on to the next slide. Incorrect
answers will display some pertinent information on the topic, then the question
will be displayed again until the correct answer is chosen.
 That’s pretty much it. Enjoy your review!
P.S. – You might want to try
to remember which
questions you answered
incorrectly. You might see
them again very soon!
CONTINENTAL DRIFT:
• Alfred Wegener first supported early mapmakers ideas that the
continents fit together like tiny puzzle pieces
• His continental drift theory stated that the Earth’s continents were once
all connected in a single landmass called Pangaea, and that when they
inevitably split, they continued to drift apart to where they are today.
• Wegener used the following evidence to support his theories:
1) Similar rock type and ages on different continents
2) Glacial scaring on continents that are too warm for the existence of
glaciers.
3) Coal deposits on continents that are too cold to sustain the environment
that would produce coal deposits
4) Similar fossils found on continents that are separated by vast oceans.
•
Unfortunately, Wegener couldn’t explain how the continents moved or
what caused their motion, so his ideas were often rejected.
SEAFLOOR
SPREADING:
 Sonar and magnetic studies of
oceanic rock led to theories of
seafloor spreading
 New ocean crust is formed at
ocean ridges and destroyed at
deep sea trenches
 Magnetic patterns on the seafloor are symmetric in relation to ocean ridges,
indicating that ocean crust on either side of the ridge is moving away from the ridge
at essentially the same rate
 Continual feeding of magma into the ridge causes the ridge to grow, and more
seafloor to be produced
 Continents were just along for the ride, floating on a sheet of moving crust
 This concept answered the how question of continental drift, but the why was still a
mystery
PLATE TECTONICS:
• The earth’s crust and rigid upper mantle are broken into
enormous slabs called plates (12 major, several minor)
• Interaction at plate boundaries as they move
Divergent
Boundary
Transform
Boundary
Convergent
Boundary
• 2 plates that are moving apart – most found on the
seafloor, as ocean ridges



New crust formation
Increased seafloor basin
Those not on the seafloor are called Rift valleys (east Africa)
formed from a magma dome
• Two plates moving toward one another
• Three different types based on the types of plates
converging (Click on each to see illustration)
Oceanic - Oceanic
Oceanic - Continental
Continental – Continental
If your are ready
for the big
picture, click
here!!!
• Two plates slide horizontally past each other
• Releases massive amounts of energy when plates do finally let go
• Leads to deformed and fractured crust rather than uplift and subduction
• Characterized by long (100 km) fault lines with shallow earthquakes
• San Andreas Fault in California is
infamous for numerous
earthquakes along it’s boundary
Oceanic – Oceanic Convergence
• One plate descends under the other in a process called subduction
• Features formed as the dense basaltic crusts come together are an oceanic
trench, an island arc, or a rift valley
• The subducted plate is recycled as it melts again to form magma
• The re-melted magma comes to the surface and cools forming the
aforementioned sea volcano and island arc
Oceanic – Continental Convergence
• As the oceanic and continental slab converge, the less dense continental
rides up on the other and forces the oceanic to subduct
• Produces mountain volcanoes at or near the continental plate
• Leads to the formation of an off-shore deep sea trench caused by the
subduction of the ocean floor
Continental – Continental Convergence
• When neither continental crust will give, plates crash into each other
• Due to their relative buoyancy, they are both thrust upward creating folded
mountains
Hey!! Nice
Mountains!!
Mantle Convection
• Put all the previous features together and you have the
process for plate tectonics via convection currents
CLICK
• This is also called
ME
QUIZ TIME!!!
What is the name of this ancient
continent before it broke apart?
A) Pancreas
B) Gondwanaland
C) Pangaea
D) Pluto
Sorry!!!
• Nice try!
• Try to remember what we
talked about in class.
• If you would like a hint,
click the “HINT” button,
otherwise click the back
button to try again
HINT
CONTINENTAL DRIFT:
• Alfred Wegener first supported early mapmakers ideas that the
continents fit together like tiny puzzle pieces
• His continental drift theory stated that the Earth’s continents were once
all connected in a single landmass called Pangaea, and that when they
inevitably split, they continued to drift apart to where they are today.
• Wegener used the following evidence to support his theories:
1) Similar rock type and ages on different continents
2) Glacial scaring on continents that are too warm for the existence of
glaciers.
3) Coal deposits on continents that are too cold to sustain the environment
that would produce coal deposits
4) Similar fossils found on continents that are separated by vast oceans.
•
Unfortunately, Wegener couldn’t explain how the continents moved or
what caused their motion, so his ideas were often rejected.
YES!!!!!
• Nicely done!
• Gondwanaland was only the southern continents,
Pangaea was all of the continents together
• Eventually we will all be stuck together again. Not to
worry, won’t happen for another 200 million years or so
• Ready for the next question?
Why was glacial evidence and coal bed evidence
important for Wegener's theories?
A) Coal is an important natural resource, and takes a long
time to make.
B) Glaciers haven’t been around for a long time, so that
proves the continents are very old.
C) The existence of coal and glaciers on continents that
have opposite climates for them, proves that they have
traveled over the years.
D) All of the above
Sorry!!!
• Nice try!
• Try to remember what we
talked about in class.
• If you would like a hint,
click the “HINT” button,
otherwise click the back
button to try again
HINT
CONTINENTAL DRIFT:
• Alfred Wegener first supported early mapmakers ideas that the
continents fit together like tiny puzzle pieces
• His continental drift theory stated that the Earth’s continents were once
all connected in a single landmass called Pangaea, and that when they
inevitably split, they continued to drift apart to where they are today.
• Wegener used the following evidence to support his theories:
1) Similar rock type and ages on different continents
2) Glacial scaring on continents that are too warm for the existence of
glaciers.
3) Coal deposits on continents that are too cold to sustain the environment
that would produce coal deposits
4) Similar fossils found on continents that are separated by vast oceans.
•
Unfortunately, Wegener couldn’t explain how the continents moved or
what caused their motion, so his ideas were often rejected.
Correct!
 Super job!
 Since glaciers and coal deposits can only occur in
extremely specific climates, the only way for these two
continents to have exactly opposite conditions from what
they have currently is that they have migrated due to
plate tectonics.
Study the map below and explain why the Pacific
seafloor has a larger red area (younger rock) than
the Atlantic seafloor?
A) It is hotter.
B) More earthquakes,
therefore more friction.
C) More resistance in the
Atlantic basin.
D) The seafloor in the
Pacific is spreading faster.
OOPS!!!
• Valiant effort!
• Try to remember what we
talked about in class.
• If you would like a hint,
click the “HINT” button,
otherwise click the back
button to try again
HINT
SEAFLOOR
SPREADING:
 Sonar and magnetic studies of
oceanic rock led to theories of
seafloor spreading
 New ocean crust is formed at
ocean ridges and destroyed at
deep sea trenches
 Magnetic patterns on the seafloor are symmetric in relation to ocean ridges,
indicating that ocean crust on either side of the ridge is moving away from the ridge
at essentially the same rate
 Continual feeding of magma into the ridge causes the ridge to grow, and more
seafloor to be produced
 Continents were just along for the ride, floating on a sheet of moving crust
 This concept answered the how question of continental drift, but the why was still a
mystery
Yup, you got it!
• Some parts of the Pacific seafloor are
spreading at twice the rate the Atlantic is.
• This also creates oceanic trenches that are
very deep due to the subduction rates of
the ocean floor.
• Marianas Trench is one of them
• Next question!!!!!!!
With the big picture in mind, what plays the
biggest part of keeping the movement of the
plates going?
A)
B)
C)
D)
Upwelling or Ridge - Push
Subduction or Slab – Pull
Gravity
All of the choices, or equal forces producing movement
Bummer!!!
• Keep trying!
• Try to remember what we
talked about in class.
• This is a thinker, no hint
available. Think about
the forces involved and
what keeps them going.
That was great!!
• Another correct answer, your pretty good at this.
• The forces of the magma pushing the ridge apart and pulling
the slab down are a given. However, the force of gravity is
probably the largest force involved due to the large masses
involved, but it’s a tough call. We will leave it to the Scientists
with all that time on their hands. We have things to do.
• ON WITH THE TEST!!!!!!
CLICK HERE